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Chia (Salvia hispanica L.) seed mucilage as a fat replacer in yogurts: Effect on their nutritional, technological, and sensory properties

Open ArchivePublished:December 23, 2020DOI:https://doi.org/10.3168/jds.2020-19240

      ABSTRACT

      Growing consumer demand for healthy and nutritious products has motivated scientists and food manufacturers to design novel dairy products with higher fiber levels and lower fat content that are free of chemical additives. Chia seed mucilage (CSM) is a healthy natural gel extensively used as a dietary source of soluble fiber, a bulking agent, and a fat replacer in a large variety of foods. In this study, we evaluated the effect of CSM on the nutritional, technological, and sensory properties of skimmed yogurts. The addition of 7.5% CSM to a yogurt formula lowered the degree of syneresis of the resulting yogurt during storage compared with full-fat yogurts. The nutritive value of the enriched yogurts improved due to higher levels of dietary fiber compared with full-fat and skimmed yogurts. Moreover, rheological measurements revealed greater consistency, firmness, and viscosity, as well as the formation of a highly structured network and better resistance to stress in yogurts containing 7.5% CSM. The sensory acceptance of the yogurts enriched with 7.5% CSM was similar to the reference samples in acidity, creaminess, and viscosity terms. These results confirm the feasibility of using CSM as a fat replacer to design novel skimmed yogurts.

      Key words

      INTRODUCTION

      Yogurt is an extensively consumed daily product obtained by the fermentation of milk with a combination of Lactobacillus spp. and Streptococcus spp. bacteria. In recent years, the demand for low-fat yogurts has risen because fat is associated with a high risk of obesity, arteriosclerosis, coronary heart illness, high blood pressure, and some cancer types (
      • Kaminarides S.
      • Stamou P.
      • Massouras T.
      Comparison of the characteristics of set type yoghurt made from ovine milk of different fat content.
      ). Nevertheless, reducing the fat content of yogurt can lead to unpleasant changes in its physical and sensory properties (
      • Zhao L.
      • Feng R.
      • Ren F.
      • Mao X.
      Addition of buttermilk improves the flavor and volatile compound profiles of low-fat yogurt.
      ). To overcome these problems, hydrocolloids are widely used as fat replacers in the dairy food industry owing to their gelling and stabilizing characteristics and because they improve different yogurt properties, such as texture, mouth feel, appearance, viscosity, and consistency (
      • Sanchez C.
      • Zuniga-Lopez R.
      • Schmitt C.
      • Despond S.
      • Hardy J.
      Microstructure of acid-induced skim milk-locust bean gum-xanthan gels.
      ).
      Chia (Salvia hispanica L.) is an herbaceous plant from southern Mexico and northern Guatemala (
      • Capitani M.I.
      • Spotorno V.
      • Nolasco S.M.
      • Tomás M.C.
      Physicochemical and functional characterization of by-products from chia (Salvia hispanica L.) seeds from Argentina.
      ). When chia seeds come into contact with water, they produce a transparent mucilaginous gel mostly composed of soluble fiber. This gel possesses an excellent water-holding capacity and good viscosities, even at low concentrations (
      • Segura-Campos M.R.
      • Acosta-Chi Z.
      • Rosado-Rubio G.
      • Chel-Guerrero L.
      • Betancur-Ancona D.
      Whole and crushed nutlets of chia (Salvia hispanica) from Mexico as a source of functional gums.
      ). These nutritional and technological properties make chia seed mucilage (CSM) a promising candidate for food applications, with potential applications as a thickener, gel former, fat replacer, and chelator (
      • Capitani M.I.
      • Spotorno V.
      • Nolasco S.M.
      • Tomás M.C.
      Physicochemical and functional characterization of by-products from chia (Salvia hispanica L.) seeds from Argentina.
      ). Recently, CSM and other plant-based gels have been used as fat substitutes in yogurts owing to their ability to improve the rheological properties and stability of dairy products, while reducing calories (
      • Darwish A.M.G.
      • Khalifa R.E.
      • El Sohaimy S.A.
      Functional properties of chia seed mucilage supplemented in low fat yoghurt.
      ;
      • Kim S.Y.
      • Hyeonbin O.
      • Lee P.
      • Kim Y.S.
      The quality characteristics, antioxidant activity, and sensory evaluation of reduced-fat yogurt and nonfat yogurt supplemented with basil seed gum as a fat substitute.
      ). However, it is important to highlight that yogurts enriched with CSM have a fat content between 1 and 3% (
      • Darwish A.M.G.
      • Khalifa R.E.
      • El Sohaimy S.A.
      Functional properties of chia seed mucilage supplemented in low fat yoghurt.
      ), and they are considered low-fat yogurts because they contain no more than 3 g of fat per 100 g for solids or 1.5 g of fat per 100 mL for liquids (
      • European Parliament, Council of the European Union
      Regulation (EC) No 1924/2006 of the European Parliament and of the Council of 20 December 2006 on nutrition and health claims made on foods.
      ). As far as we know, CSM has not been used as a fat substitute in fermented skim milk products for achieving equal or better technological qualities in comparison with full-fat yogurts.
      Hence, this work evaluated the possibility of adding CSM as a fat replacer to skimmed yogurts and investigated the effect of its incorporation on the nutritional, technological, and organoleptic properties of skimmed yogurts during storage.

      MATERIALS AND METHODS

      Yogurt Ingredients, Media, and Chemicals

      For the yogurt formulation, full-fat and skim milk powder (Central Lechera Asturiana, Siero, Spain) and commercial chia seeds (Pedon S.P.A, Molvena, Italy) were purchased from a local Spanish market. Lyophilized Streptococcus salivarius ssp. thermophilus (CECT 801) and Lactobacillus delbrueckii ssp. bulgaricus (CECT 4005), obtained from Colección Española de Cultivos Tipo (CECT, University of Valencia, Burjassot, Spain), were used to prepare starter cultures.
      For culture media, M17 and de Man, Rogosa, and Sharpe (MRS; broth and agar) and d-lactose monohydrate were used, all of which were supplied by Scharlab (Barcelona, Spain). All other chemicals were purchased from Sigma-Aldrich (Madrid, Spain).

      Preparation of the Starter Cultures

      Starter cultures were prepared by adding 1 mL of M17 broth, enriched with d-lactose monohydrate (1%, wt/vol; M17-lactose), to the phial containing the lyophilized S. salivarius ssp. thermophilus, and 1 mL of MRS broth to the freeze-dried L. delbrueckii ssp. bulgaricus phial. They were mixed to obtain homogeneous suspensions, which were transferred to test tubes containing 10 mL of M17-lactose for S. salivarius ssp. thermophilus and 10 mL of MRS broth for L. delbrueckii ssp. bulgaricus. The M17-lactose tube was incubated aerobically at 37°C for 24 h, and the MRS tube was incubated anaerobically at 37°C for 72 h using anaerobic jars. Test tubes were centrifuged (2,057 × g for 5 min at 20°C), supernatants were discarded, and 10 mL of each broth was added to the pellet. Serial dilutions were done, and colonies were enumerated by plating 1 mL in M17-lactose agar and 1 mL in MRS agar. Finally, plates were incubated aerobically at 37°C for 24 h (S. salivarius ssp. thermophilus) and anaerobically at 37°C for 72 h (L. delbrueckii ssp. bulgaricus) using anaerobic jars.

      Mucilage Extraction from Chia Seeds

      To extract CSM, whole chia seeds were submerged in distilled water (water:seed ratio of 30:3), and the mixture was gently stirred at 500 rpm for 3 h at 80°C. After cooling to 20°C, it was centrifuged at 12,857 × g for 15 min at 20°C (Centrifuge 5804 R, Eppendorf AG, Hamburg, Germany). The obtained CSM was freeze-dried (LyoQuest-55, Telstar, Terrassa, Spain) for 48 h before being stored in sterile containers at room temperature before use.

      Yogurt Manufacture

      Five yogurt types were prepared in this study: 1 full-fat yogurt (FFY), 1 skimmed yogurt (SY), and 3 formulations of SY enriched with different CSM concentrations (2.5, 5.0, and 7.5%, wt/vol).
      Milk was prepared by adding 100 g of commercial full-fat or skim milk powder to 1 L of distilled water. The mixture was heated in a bath (JP Selecta S.A., Abrera, Spain) at 85°C for 30 min. Afterward, milk was cooled to 45°C and CSM was added to the mixture at the previously indicated concentrations. No CSM was added to the FFY and SY samples. Each yogurt culture was added at a concentration of 107 cfu/mL. Next, 125 mL of the final mixture was poured into sterilized glass containers, which were placed in an incubator at 40°C and fermented until pH values of 4.5 to 4.6 were achieved. The glass containers were sterilized at 121°C for 15 min by using an autoclave. Finally, yogurts were stored at 4°C until analyses at 1, 7, 14, and 21 d. Each formulation was manufactured in duplicate.

      Physicochemical Characterization of Yogurts

      A Crison Basic 20+ pH meter (Crison S.A., Barcelona, Spain) was used to measure the pH of yogurts. For the total titratable acidity (TTA) determinations, 10 g of each sample was mixed with 40 mL of distilled water and titrated with a 0.1 N NaOH solution until pH 8.30 ± 0.01 (
      • Pelaes Vital A.C.
      • Goto P.A.
      • Hanai L.N.
      • Gomes-da-Costa S.M.
      • de Abreu Filho B.A.
      • Nakamura C.V.
      • Matumoto-Pintro P.T.
      Microbiological, functional and rheological properties of low fat yogurt supplemented with Pleurotus ostreatus aqueous extract.
      ). Titratable acidity was expressed as grams of lactic acid per 100 g of yogurt. Syneresis was determined by centrifuging 5-mL samples of yogurt at 3,214 × g for 20 min at 4°C (Centrifuge 5804 R, Eppendorf AG). The results are reported as the volume of separated whey per 100 g of yogurt.
      The color parameters (L*, a*, and b*; lightness, red-green color, yellow-blue color, respectively) of yogurts were measured by a spectrocolorimeter (CM-3600d, Minolta Co., Tokyo, Japan) with an observer 10° and illuminant D65. Whiteness index (WI) and color variations (ΔE*) were calculated by Equations [1] and [2], respectively:
      WI = 100 − [(100 − L*)2 + a*2 + b*2]0.5,
      [1]


      ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]0.5.
      [2]


      Nutritional Composition of Yogurts

      The nutritional value of yogurts (moisture, protein, fat, ash, and total dietary fiber) was determined following AOAC procedures (
      • AOAC International
      Official Methods of Analysis.
      ). Protein, fat, fiber, and ash contents were analyzed using lyophilized yogurt samples. Finally, carbohydrates were estimated by difference. All the tests were run in triplicate.

      Rheological and Viscoelastic Measurements

      The rheological and viscoelastic measurements were taken by a stress-controlled rheometer RS1 (Thermo Haake, Karslruhe, Germany). Assays were performed at 4°C using a C60/2° Ti cone-plate geometry with a 2-mm gap. Samples were placed in the measuring system and allowed to stand for 300 s for structure recovery and temperature equilibration before being tested. All rheological measurements were done in triplicate.

      Steady Shear Rheological Tests

      The steady shear rheological tests were performed within the range of 0.1 to 200 s−1 for 120 s. To rule out any possible dependence on flow time, a 4-step operation (2 upward and 2 downward curves) was applied to samples and flow curve was fitted to the Hershel-Bulkley model (
      • Sah B.N.P.
      • Vasiljevic T.
      • McKechnie S.
      • Donkor O.N.
      Physicochemical, textural and rheological properties of probiotic yogurt fortified with fibre-rich pineapple peel powder during refrigerated storage.
      ). Finally, the yield stress (τ0), consistency (K), and flow behavior indices (n) were calculated, as was apparent viscosity (ηapp50) (Equation [3]) (
      • Morell P.
      • Hernando I.
      • Llorca E.
      • Fiszman S.
      Yogurts with an increased protein content and physically modified starch: rheological, structural, oral digestion and sensory properties related to enhanced satiating capacity.
      ).
      ηapp50 = (K × 50n−1).
      [3]


      Dynamic Rheological Tests

      To determine the linear viscoelastic region, stress sweeps were performed within a stress range from 0.01 to 10 Pa at 1 Hz. Frequency sweep tests were conducted at 1 Pa (in the linear viscoelastic region) to cover a 0.1- to 10-Hz frequency range at 4°C.
      The viscoelastic parameters, namely elastic or storage modulus (G′), viscous or loss modulus (G″), complex modulus (|G*|), loss tangent (tan δ), and complex viscosity (|η*|), were obtained from the rheometer software (RheoWin 3 Data Manager, Thermo Haake).

      Creep and Recovery Tests

      Creep and recovery tests were carried out by applying constant stress (1 Pa within the linear viscoelastic region), which was maintained for 300 s. Afterward, stress was stopped and samples were released for recovery for 300 s.
      The Burger model parameters (G0 = instantaneous elastic modulus of the Maxwell unit; η0 = residual viscosity) were taken from the rheometer software (RheoWin 3 Data Manager). The system's final percentage of recovery (R) was calculated with Equation [4]:
      R (%) = (JmaxJ/Jmax) × 100,
      [4]


      where Jmax is the maximum deformation corresponding to the compliance value for the longest time (300 s) in the creep rest; J is the residual deformation (
      • Kurt A.
      • Cengiz A.
      • Kahyaoglu T.
      The effect of gum tragacanth on the rheological properties of salep based ice cream mix.
      ).

      Sensory Evaluation

      The sensory evaluation of yogurts was conducted by a semi-trained panel. The participants were between 24 and 50 yr old and included 20 women and 10 men. Panel selection emphasized interest in the sensory evaluation of yogurts, availability, being a nonsmoker, and lack of allergies, following the general guidelines of UNE-ISO 8586:2012 (
      • ISO
      UNE-ISO 8586: Sensory analysis. General guidelines for the selection, training and monitoring of selected assessors and expert sensory assessors.
      ). Training sessions were performed to introduce the panelists to the sensory analysis and to identify and score the quality attributes that define the samples. A structured 9-point hedonic scale (1 = very unpleasant; 9 = very pleasant; UNE-ISO 4121:2003,
      • ISO
      UNE-ISO 4121: Sensory analysis. Guidelines for the use of quantitative response scale.
      ) was used to evaluate the appearance, color, viscosity, granularity, creaminess, acidity, and global acceptance attributes. The panelists tested 3 different samples: FFY (prepared with whole milk powder), SY (manufactured with skim milk powder), and SY + 7.5% CSM (produced with skim milk powder enriched with 7.5% CSM). The evaluated samples were selected according to the data observed in the nutritional and rheological tests. The sensory analysis was carried out 24 h after preparing yogurts, which were stored at 4°C. Samples were presented to the panelists in a plastic cup, coded with 3 random digits. Sensory evaluations were made by following the Institute of Food Science and Technology Guidelines for Ethical and Professional Practices for the Sensory Analysis of Foods (
      • Institute of Food Science and Technology
      Guidelines for ethical and professional practices for the sensory analysis of foods.
      ). Every panelist gave written consent before conducting the sensory analysis.

      Statistical Analysis

      The results obtained from the physicochemical characterization, the nutritional composition, and the rheological assays of yogurts were analyzed by a multifactor ANOVA to evaluate differences among the samples and storage times. The results of the influence of using CSM on the sensory characteristics of yogurts were analyzed by a one-way ANOVA. The least significance procedure was used to test for any differences between averages at a 5% level of significance. Data were statistically processed by Statgraphics Centurion XVI (Statgraphics Technologies Inc., The Plains, VA).

      RESULTS AND DISCUSSION

      Physicochemical Characterization of Yogurts

      The changes in pH, TTA, and syneresis of the different manufactured yogurts are shown in Figure 1. The pH values of all the samples progressively declined at 4°C, with a significant (P < 0.05) decrease throughout the storage period. The differences observed among samples were significant (P < 0.05) after 14 d of storage.
      Figure thumbnail gr1
      Figure 1(A) pH, (B) total titratable acidity (TTA), and (C) syneresis of the different yogurts during 21 d of storage at 4°C. Mean values (n = 3) ± standard deviation. Lowercase letters (a, b, c, d) indicate significant differences among storage times (P < 0.05). Uppercase letters (A, B, C) indicate significant differences among samples (P < 0.05). FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      A slight rise in TTA occurred over the storage time as a result of greater lactic acid production, which could be caused by continued fermentation and lactic bacteria growth. Higher TTA leads to greater casein micelle matrix contraction, which means more whey is released (
      • Fox P.F.
      • Guinee T.P.
      • Cogan T.M.
      • McSweeney P.L.H.
      Cheese yield.
      ). For instance, the lactic acid concentration in the stored yogurts initially ranged from 0.617 ± 0.002 g/100 g to 0.767 ± 0.023 g/100 g, whereas it ranged from 0.672 ± 0.023 g/100 g to 0.815 ± 0.009 g/100 at the end of the study (Figure 1B).
      Furthermore, slightly significant differences (P < 0.05) were observed in sample types. The TTA values of the SY, with or without fortification with CSM, were higher than those exhibited by the FFY sample. In line with this,
      • Yazici F.
      • Akgun A.
      Effect of some protein based fat replacers on physical, chemical, textural, and sensory properties of strained yoghurt.
      reported that higher TTA values could be attributed to the moisture content of low-fat and nonfat yogurts.
      Regarding samples' degree of syneresis, more whey became separated throughout the storage time for FFY and SY samples, which could be explained by increased acidity during storage, which would bring about casein micelle matrix contraction and subsequent release of whey (
      • Canbulat Z.
      • Ozcan T.
      Effects of short-chain and long-chain inulin on the quality of probiotic yoghurt containing Lactobacillus rhamnosus..
      ). Conversely, the sample prepared with the highest CSM concentration (7.5%) had a lower degree of syneresis during the study, and this depletion came close to 2% after 21 d of analysis. The latter finding could be explained by interactions between casein micelles (positively charged) and CSM (negatively charged), which in turn enhanced matrix stabilization and reduce separated whey (Figure 1C).
      With regard to the color parameters, the L* values ranged from 86.9 ± 0.5 to 89.8 ± 0.1, and the WI values were between 83.4 ± 1.2 and 86.4 ± 0.6. Moreover, the ΔE* values ranged from 0.5 ± 0.1 to 1.8 ± 0.5 throughout the evaluation (Figure 2). These results suggest that the ΔE* of yogurts stored at 4°C for 21 d did not exceed the just noticeable difference (
      • Baldevbhai P.J.
      • Aanand R.S.
      Color image segmentation for medical images using L*a*b* color space.
      ).
      Figure thumbnail gr2
      Figure 2Color parameters: (A) luminosity (L*), (B) whiteness index (WI), and (C) color variations (ΔE*) of the different yogurts stored during 21 d of storage at 4°C. Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.

      Nutritional Composition of Yogurts

      Figure 3 presents the results of the nutritional composition of yogurts. As expected, storage time did not significantly affect (P > 0.05) moisture, protein, fat, and ash contents, which remained practically constant over the study period for each sample type. Significant differences (P < 0.05) in protein content were noted among formulations, with SY having the least protein. In addition, the yogurts prepared with CSM exhibited slightly higher protein values than SY (Figure 3B), which may be due to the protein content of CSM, as indicated by
      • Felisberto M.H.F.
      • Wahanik A.L.
      • Gomes-Ruffi C.R.
      • Clerici M.T.P.S.
      • Chang Y.K.
      • Steel C.J.
      Use of chia (Salvia hispanica L.) mucilage gel to reduce fat in pound cakes.
      in their study characterizing lyophilized CSM.
      Figure thumbnail gr3
      Figure 3Nutritional composition (g/100 g of fresh yogurt) for diverse yogurt samples during 21 d of storage at 4°C. Mean values (n = 3) ± standard deviation. Lowercase letters (a, b, c) indicate significant differences among the storage time (P < 0.05). Uppercase letters (A, B, C, D) indicate significant differences among the samples (P < 0.05). FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      Full-fat yogurt had a fat content of 3.9 ± 0.2 g/100 g throughout storage. The fat content of the modified yogurts increased with the CSM content (Figure 3C). This finding could be explained through data reported by several authors on proximate lyophilized CSM composition (
      • Capitani M.I.
      • Ixtaina V.Y.
      • Nolasco S.M.
      • Tomás M.C.
      Microstructure, chemical composition and mucilage exudation of chia (Salvia hispanica L.) nutlets from Argentina.
      ;
      • Felisberto M.H.F.
      • Wahanik A.L.
      • Gomes-Ruffi C.R.
      • Clerici M.T.P.S.
      • Chang Y.K.
      • Steel C.J.
      Use of chia (Salvia hispanica L.) mucilage gel to reduce fat in pound cakes.
      ). A similar trend was noted for ash content. The yogurts made with CSM presented a slightly higher ash content than the control and SY samples (Figure 3D).
      Figure 3E shows that the higher the mucilage concentration, the larger the fiber content. This fact could be accounted for by the high dietary fiber levels present in the extracted mucilage (
      • Felisberto M.H.F.
      • Wahanik A.L.
      • Gomes-Ruffi C.R.
      • Clerici M.T.P.S.
      • Chang Y.K.
      • Steel C.J.
      Use of chia (Salvia hispanica L.) mucilage gel to reduce fat in pound cakes.
      ), which would improve the nutritional characteristics of the novel yogurts. Storage time did not significantly affect the fiber content of yogurts.

      Rheological Measurements

      Steady Shear Rheological Tests

      Table 1 shows the results of the rheological parameters from the steady shear test of yogurts. Yield stress (τ0) is a typical characteristic of these products and is well correlated with their early firmness during sensory tests (
      • Costa M.F.
      • Pimentel T.C.
      • Guimaraes J.T.
      • Balthazar C.F.
      • Rocha R.S.
      • Cavalcanti R.N.
      • Esmerino E.A.
      • Freitas M.Q.
      • Raices R.S.L.
      • Silva M.C.
      • Cruz A.G.
      Impact of prebiotics on the rheological characteristics and volatile compounds of Greek yogurt.
      ;
      • Harte F.
      • Clark S.
      • Barbosa-Cánovas G.V.
      Yield stress for initial firmness determination on yogurt.
      ). As observed throughout the evaluation period, the formulations with higher yield stress (τ0) were FFY and the yogurt enriched with 7.5% CSM. This outcome could be associated with the presence of an interactive or cross-linked structure (
      • Yu H.Y.
      • Wang L.
      • McCarthy K.L.
      Characterization of yogurts made with milk solids non-fat by rheological behavior and nuclear magnetic resonance spectroscopy.
      ), which was more pronounced in the samples with the highest amount of the CSM. A slightly reduction in this parameter was observed during the storage time, which could be related to the preservation of the cross-linked structure with time.
      Table 1Rheological parameters from the steady shear tests of the different yogurt formulations during 21 storage days at 4°C: yield stress (τ0), consistency coefficient (K), flow behavior index (n), and apparent viscosity (ηapp50)
      Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      ItemDay of analysisYogurt type
      FFYSYSY + CSM 2.5%SY + CSM 5.0%SY + CSM 7.5%
      τ0, Pa13.192 ± 0.047
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.982 ± 0.036
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.469 ± 0.030
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.853 ± 0.091
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.157 ± 0.029
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      73.107 ± 0.065
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.970 ± 0.058
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.449 ± 0.048
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.812 ± 0.043
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.089 ± 0.042
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      143.069 ± 0.031
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.778 ± 0.020
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.204 ± 0.052
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.767 ± 0.038
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.044 ± 0.017
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      212.951 ± 0.113
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.731 ± 0.059
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.163 ± 0.077
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.722 ± 0.052
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.968 ± 0.028
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      K, Pa·s14.667 ± 0.138
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.256 ± 0.092
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.272 ± 0.036
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.388 ± 0.064
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.479 ± 0.105
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      74.921 ± 0.106
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.222 ± 0.014
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.559 ± 0.042
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.626 ± 0.050
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.885 ± 0.092
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      145.216 ± 0.022
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.160 ± 0.073
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.303 ± 0.049
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.070 ± 0.087
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.088 ± 0.100
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      215.434 ± 0.063
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.364 ± 0.040
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.589 ± 0.047
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.169 ± 0.029
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.333 ± 0.041
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      n10.624 ± 0.009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.644 ± 0.005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.624 ± 0.007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.612 ± 0.019
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.613 ± 0.026
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      70.631 ± 0.019
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.640 ± 0.011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.624 ± 0.010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.648 ± 0.010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.624 ± 0.005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      140.656 ± 0.028
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.686 ± 0.038
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.673 ± 0.006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.619 ± 0.028
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.644 ± 0.023
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      210.671 ± 0.013
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.696 ± 0.026
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.755 ± 0.073
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.663 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.641 ± 0.014
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      ηapp50, Pa·s10.160 ± 0.011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.064 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.071 ± 0.007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.147 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.195 ± 0.023
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      70.135 ± 0.006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.054 ± 0.001
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.059 ± 0.005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.128 ± 0.002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.165 ± 0.006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      140.104 ± 0.009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.045 ± 0.011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.047 ± 0.014
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.102 ± 0.016
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.147 ± 0.012
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      210.090 ± 0.010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.028 ± 0.009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.030 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.085 ± 0.007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.106 ± 0.009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      a–d Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      A–E Uppercase letters indicate significant differences among the samples (P < 0.05).
      1 Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      The consistency index (K) of yogurts is linked with different intermolecular interactions and attraction forces between proteins (
      • Costa M.F.
      • Pimentel T.C.
      • Guimaraes J.T.
      • Balthazar C.F.
      • Rocha R.S.
      • Cavalcanti R.N.
      • Esmerino E.A.
      • Freitas M.Q.
      • Raices R.S.L.
      • Silva M.C.
      • Cruz A.G.
      Impact of prebiotics on the rheological characteristics and volatile compounds of Greek yogurt.
      ). Higher K values were observed for the reference sample (FFY) during the study. Moreover, marked concentration dependency was noticed among the products containing CSM. Addition of CSM to yogurts significantly (P < 0.05) increased the K values, which became higher when larger amounts of CSM were used. This finding could be explained by the capacity of swollen CSM particles to act as fillers, which reduces the protein matrix mobility and increases enriched yogurts' consistency (
      • Morell P.
      • Hernando I.
      • Llorca E.
      • Fiszman S.
      Yogurts with an increased protein content and physically modified starch: rheological, structural, oral digestion and sensory properties related to enhanced satiating capacity.
      ). Furthermore, significant differences (P < 0.05) were found among samples during storage. As seen in Table 1, higher K values were detected in the samples stored for 21 d at 4°C. Similarly,
      • Cardines P.H.F.
      • Baptista A.T.A.
      • Gomes R.G.
      • Bergamasco R.
      • Vieira A.M.S.
      Moringa oleifera seed extracts as promising natural thickening agents for food industry: Study of the thickening action in yogurt production.
      observed higher K values for all their samples throughout storage due to whey spontaneously migrating to the surface of the product.
      The flow behavior index (n) indicates the rheological nature of the fluid. As the fluid approaches Newtonian behavior, the n value approaches 1 (
      • Kaur S.
      • Kaler R.S.S.
      Dextran and its effect on the flow behaviour of molasses and crystallization rate.
      ). The n values decreased below 1 for all tested yogurts, which indicates shear-thinning behavior once yield stress was overtaken. Generally, n values became lower with higher CSM concentrations. Similar results have been described by
      • Paseephol T.
      • Small D.M.
      • Sherkat K.
      Rheology and texture of set yogurt as affected by inulin addition.
      regarding the addition of oligofructose and medium-chain inulin to yogurts. Conversely, a rise in those values was observed over storage time for each sample, which accords with the results reported by
      • Paseephol T.
      • Small D.M.
      • Sherkat K.
      Rheology and texture of set yogurt as affected by inulin addition.
      .
      A marked increase in the manufactured samples' viscosity (ηapp50) was observed in the SY products containing more CSM (Table 1). As the mucilage concentration rose, viscosity increased owing to the interactions between polysaccharides and dairy proteins (
      • Sodini I.
      • Remeuf F.
      • Haddad S.
      • Corrieu G.
      The relative effect of milk base, starter, and process on yogurt texture: A review.
      ). It is worth mentioning that by the end of storage, higher ηapp50 values were observed in the samples formulated with 7.5% CSM compared with FFY (Table 1).
      Lastly, noticeable differences were found as a result of storage. The longer the storage, the lower the manufactured yogurts' viscosity values (
      • Aryana K.J.
      • Barnes H.T.
      • Emmick T.K.
      • McGrew P.
      • Moser B.
      Lutein is stable in strawberry yogurt and does not affect its characteristics.
      ), which could be explained by the depleted water-binding capacity of the proteins present in each formulation (
      • Jaster H.
      • Arend G.D.
      • Rezzadori K.
      • Chaves V.C.
      • Reginatto R.H.
      • Petrus J.C.C.
      Enhancement of antioxidant activity and physicochemical properties of yogurt enriched with concentrated strawberry pulp obtained by block freeze concentration.
      ).

      Dynamic Rheological Tests

      Table 2 shows the viscoelastic properties of the different manufactured yogurts. For comparative purposes, the storage modulus (G′) and loss modulus (G″) values were considered at a frequency of 1 Hz. A predominant elastic behavior (G′ > G″), which is common in weak viscoelastic systems (
      • Morell P.
      • Hernando I.
      • Llorca E.
      • Fiszman S.
      Yogurts with an increased protein content and physically modified starch: rheological, structural, oral digestion and sensory properties related to enhanced satiating capacity.
      ), was observed throughout the study. The FFY sample presented higher G′ and G″ values than the SY sample. Indeed, increasing G′ and G″ values were noticed when the CSM concentrations were higher. This finding can be explained by the interactions taking place between negatively charged mucilage and the positively charged surface of casein micelles, which lead to a highly structured network that provides samples with good gel strength and makes them more viscous (
      • Foster T.
      • Wolf B.
      Hydrocolloid gums: Their role and interaction in foods.
      ). Furthermore, for the enriched yogurts, and despite storage time, the highest G′ and G″ values were exhibited by the yogurts formulated with 7.5% CSM. Thus, large amounts of CSM could increase skimmed yogurts' firmness due to the strength of the developed network structure, which would diminish the mobility of particles and the syneresis rate, as already mentioned.
      Table 2Viscoelastic properties, at a frequency of 1 Hz, of the different yogurt formulations during 21 storage days at 4°C: elastic or storage modulus (G′), viscous or loss modulus (G″), complex modulus (|G*|), complex viscosity (|η*|), and loss tangent (tan δ)
      Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      ItemDay of analysisYogurt type
      FFYSYSY + CSM 2.5%SY + CSM 5.0%SY + CSM 7.5%
      G′, Pa1297 ± 91
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      81 ± 42
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      121 ± 89
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      169 ± 25ª,
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      281 ± 104
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      7453 ± 62
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      165 ± 49
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      279 ± 38
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      296 ± 90
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      445 ± 40
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      14671 ± 39
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      230 ± 91
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      354 ± 20
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      482 ± 22
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      636 ± 91
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      21721 ± 15
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      399 ± 15
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      413 ± 29
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      626 ± 53
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      770 ± 22
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      G″, Pa1183 ± 43
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      64 ± 24
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      90 ± 11
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      127 ± 36
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      199 ± 31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      7236 ± 21
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      138 ± 23
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      161 ± 50
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      232 ± 32
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      250 ± 47
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      14271 ± 36
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      178 ± 21
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      240 ± 26
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      275 ± 45
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      287 ± 28
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      21337 ± 19
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      267 ± 14
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      283 ± 12
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      302 ± 18
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      362 ± 19
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      |G*|, Pa1287 ± 14
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      109 ± 46
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      183 ± 26
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      235 ± 25
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      293 ± 48
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      7336 ± 45
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      227 ± 31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      324 ± 51
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      381 ± 23
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      361 ± 37
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      14503 ± 51
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      364 ± 42
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      446 ± 40
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      496 ± 32
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      598 ± 31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      21760 ± 15
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      413 ± 10
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      542 ± 31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      671 ± 83
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      816 ± 18
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      tan δ10.596 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.709 ± 0.002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.746 ± 0.005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.756 ± 0.007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.710 ± 0.006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      70.501 ± 0.009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.792 ± 0.002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.567 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.774 ± 0.001
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.563 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      140.434 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.756 ± 0.002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.680 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.560 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.461 ± 0.010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      210.466 ± 0.008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.708 ± 0.006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.681 ± 0.007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.510 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.473 ± 0.004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      |η*|, Pa·s161 ± 11
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      50 ± 1
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      55 ± 17
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      66 ± 16
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      75 ± 24
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      794 ± 33
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      85 ± 15
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      89 ± 16
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      94 ± 31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      100 ± 9
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      14129 ± 45
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      124 ± 26
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      128 ± 44
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      132 ± 35
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      170 ± 28
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      21252 ± 38
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      159 ± 23
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      177 ± 33
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      187 ± 19
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      250 ± 39
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      a–d Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      A–E Uppercase letters indicate significant differences among the samples (P < 0.05).
      1 Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      Prolonged cold storage significantly affected (P < 0.05) the G′ and G″ values of all the yogurts formulated in this study. Higher values were observed after 21 d of storage at 4°C, regardless of yogurt type (
      • Sah B.N.P.
      • Vasiljevic T.
      • McKechnie S.
      • Donkor O.N.
      Physicochemical, textural and rheological properties of probiotic yogurt fortified with fibre-rich pineapple peel powder during refrigerated storage.
      ). Cooling processes can bring about conformational changes in products, such as xanthan gum and gelatin, reflected by increasing G′ values of acid milk gels (
      • Pang Z.
      • Deeth H.
      • Yang H.
      • Prakash S.
      • Bansal N.
      Evaluation of tilapia skin gelatin as a mammalian gelatin replacer in acid milk gels and low-fat stirred yogurt.
      ). Hence, conformational changes in CSM molecules during cooling storage could explain the higher values found for the 7.5% CSM yogurts.
      Complex modulus (|G*|) is a measure of the product stiffness (
      • Mezger T.G.
      ). The higher the complex modulus |G*| is, the greater the yogurt firmness (
      • Costa M.F.
      • Pimentel T.C.
      • Guimaraes J.T.
      • Balthazar C.F.
      • Rocha R.S.
      • Cavalcanti R.N.
      • Esmerino E.A.
      • Freitas M.Q.
      • Raices R.S.L.
      • Silva M.C.
      • Cruz A.G.
      Impact of prebiotics on the rheological characteristics and volatile compounds of Greek yogurt.
      ). Thus, FFY and 7.5% CSM were the formulations with the best firmness. This outcome indicates that using larger amounts of CSM could increase skimmed yogurts' firmness because of the robust network structure created.
      Indeed, the firmness of all the products significantly (P < 0.05) increased during storage.
      • Walstra P.
      • Geurts T.J.
      • Noomen A.
      • Jellema A.
      • van Boekel M.A.J.S.
      Fermented milks.
      pointed out that yogurt gel firmness increased when pH values decreased. In this study, lower pH values were obtained at the end of storage, increasing |G*| values and improving gel firmness.
      Values for tan δ can be used to indicate the system's physical behavior. Values above 1 are indicative of dilute solutions, while values between 0.1 and 1 denote weak gels (
      • Irani M.
      • Razavi S.M.A.
      • Abdel-Aal E.S.M.
      • Hucl P.
      • Patterson C.A.
      Viscoelastic and textural properties of canary seed starch gels in comparison with wheat starch gel.
      ). All the formulations had tan δ values below 1, which reinforces that elastic properties prevail over viscous ones. The tan δ values for all the formulations remained practically constant throughout storage. Moreover, the addition of CSM significantly (P < 0.05) increased the complex viscosity (|η*|) of the different samples suggesting that the obtained mucilage had a thickening effect on yogurts and increased internal cohesive forces (
      • Giri S.K.
      • Tripathi M.K.
      • Kotwaliwale N.
      Effect of composition and storage time on some physico-chemical and rheological properties of probiotic soy-cheese spread.
      ). Similarly, the increase in |η*| that took place during storage could be explained by post-acidification processes (
      • Saint-Eve A.
      • Lévy C.
      • Le Moigne M.
      • Ducruet V.
      • Souchon I.
      Quality changes in yogurt during storage in different packaging materials.
      ).

      Creep and Recovery Tests

      Figure 4 shows the creep and recovery curves of the different yogurts. High compliance values [J(t)] indicate a weaker product structure (
      • Sozer N.
      Rheological properties of rice pasta dough supplemented with proteins and gums.
      ). According to this view, the SY sample presented the weakest gel structure, whereas samples formulated with increasing CSM concentrations had lower J(t) values, which reflected more elastic behavior. Notably, the FFY and 7.5% CSM samples displayed similar behavior for the first 7 d of analysis. Afterward, the J(t) values significantly (P < 0.05) decreased for the sample enriched with 7.5% CSM. For this reason, it can be stated that using CSM reinforced the gel structure of the developed yogurts.
      Figure thumbnail gr4
      Figure 4Creep and recovery curves of the different yogurts stored at 4°C for (A) 1 d; (B) 7 d; (C) 14 d; and (D) 21 d. Mean values (n = 3). FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage. J = deformation; t = time.
      Regarding the Burger model parameters (Table 3), the instantaneous shear modulus (G0) was higher when larger amounts of extracted mucilage were used. This rise could indicate increased elastic strength of the bonds forming the interfacial network structure of yogurts (
      • Karaman S.
      • Yilmaz M.T.
      • Cankurt H.
      • Kayacier A.
      • Sagdic O.
      Linear creep and recovery analysis of ketchup-processed cheese mixtures using mechanical simulation models as a function of temperature and concentration.
      ). Significant differences (P < 0.05) were observed in the G0 values throughout the study as yogurts had higher G0 values at the end of the study, suggesting the reinforcement of the gel matrix. These results agree with those previously observed.
      Table 3Burger model parameters (G0, η0), maximum compliance (Jmax), and final percentage of recovery (R) of the different yogurts stored at 4°C for 21 d
      Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      ItemDay of analysisYogurt type
      FFYSYSY + CSM 2.5%SY + CSM 5.0%SY + CSM 7.5%
      G0, Pa1114.0 ± 10.0
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      87.6 ± 5.3
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      262.6 ± 33.3
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      172.9 ± 71.2
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      282.6 ± 39.4
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      7257.1 ± 47.7
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      187.6 ± 23.8
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      264.7 ± 20.6
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      213.9 ± 22.1
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      481.4 ± 78.5
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      14291.8 ± 22.3
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      155.5 ± 48.6
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      227.5 ± 71.3
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      260.6 ± 54.1
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      671.3 ± 92.6
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      21395.3 ± 15.9
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      269.0 ± 38.6
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      348.2 ± 23.2
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      316.7 ± 66.2
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1329.0 ± 36.5
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      η0 × 105, Pa·s12.992 ± 0.199
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.024 ± 0.161
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.266 ± 0.295
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.687 ± 0.502
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.851 ± 1.376
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      74.565 ± 0.994
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.722 ± 0.358
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.222 ± 0.189
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.935 ± 0.275
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      3.912 ± 0.602
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      143.543 ± 0.502
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.928 ± 0.604
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.685 ± 0.791
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2.416 ± 0.622
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      6.735 ± 0.751
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      217.206 ± 1.094
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1.925 ± 0.365
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.014 ± 0.908
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      4.379 ± 2.326
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      5.014 ± 0.908
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      Jmax, Pa−110.0031 ± 0.0001
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0144 ± 0.0002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0047 ± 0.0002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0041 ± 0.0008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0030 ± 0.0006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      70.0040 ± 0.0008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0065 ± 0.0007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0042 ± 0.0007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0057 ± 0.0005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0031 ± 0.0002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      140.0041 ± 0.0004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0065 ± 0.0022
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0059 ± 0.0009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0047 ± 0.0025
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0025 ± 0.0010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      210.0029 ± 0.0006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0047 ± 0.0004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0040 ± 0.0011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0042 ± 0.0011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0019 ± 0.0007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      J, Pa−110.0013 ± 0.0004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0073 ± 0.0005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0022 ± 0.0005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0018 ± 0.0004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0015 ± 0.0005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      70.0020 ± 0.0008
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0036 ± 0.0006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0029 ± 0.0007
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0030 ± 0.0003
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0011 ± 0.0001
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      140.0027 ± 0.0010
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0042 ± 0.0002
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0030 ± 0.0009
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0028 ± 0.0013
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0010 ± 0.0005
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      210.0018 ± 0.0006
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0029 ± 0.0004
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0027 ± 0.0011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0026 ± 0.0011
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      0.0007 ± 0.0003
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      R, %158.07 ± 2.31
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      49.31 ± 2.29
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      52.75 ± 1.40
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      56.10 ± 5.43
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      51.21 ± 5.04
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      750.31 ± 5.02
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      45.37 ± 5.26
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      33.78 ± 6.99
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      48.37 ± 1.39
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      63.99 ± 2.35
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      1439.20 ± 6.12
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      40.81 ± 6.45
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      49.00 ± 2.30
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      40.63 ± 0.83
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      58.73 ± 4.63
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      2138.68 ± 3.10
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      42.44 ± 8.11
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      35.36 ± 6.64
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      40.08 ± 3.45
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      64.57 ± 4.64
      Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      Uppercase letters indicate significant differences among the samples (P < 0.05).
      a–d Lowercase letters indicate significant differences among the storage time expressed in days (P < 0.05).
      A–D Uppercase letters indicate significant differences among the samples (P < 0.05).
      1 Mean values (n = 3) ± standard deviation. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      In contrast, the Jmax and J values decreased when higher CSM concentrations were used (Table 3). This finding could be explained by the final product's enhanced elastic bonds, which diminished the number of irreversible broken bonds (
      • Kurt A.
      • Cengiz A.
      • Kahyaoglu T.
      The effect of gum tragacanth on the rheological properties of salep based ice cream mix.
      ). Last, the recovery rates (R, %) exhibited better elastic behavior for 7.5% CSM yogurts than FFY and SY samples. This phenomenon was clearly observed when storage time ended. Thus, as suggested by
      • Kurt A.
      • Cengiz A.
      • Kahyaoglu T.
      The effect of gum tragacanth on the rheological properties of salep based ice cream mix.
      , adding anionic polysaccharides to milk bases could increase resistance to stress due to stronger interactions among the constituents of foods.

      Sensory Analysis

      The sensory analysis is an essential tool for determining the acceptance of new foods. For this reason, a sensory evaluation of FFY (control), SY, and the yogurt prepared with 7.5% CSM was carried out. The incorporation of extracted CSM into yogurts did not modify acidity, creaminess, or viscosity compared with the FFY sample. Nevertheless, the appearance, color, and granularity of the manufactured yogurts were affected when CSM was added (Table 4).
      Table 4Score of the attributes tested in FFY and the yogurts formulated with increasing CSM concentrations (2.5%, 5.0%, 7.5%)
      0 = very unpleasant; 9 = very pleasant. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      Yogurt typeAttribute
      AppearanceColorViscosityGranularityCreaminessAcidityGlobal acceptance
      FFY7.5 ± 0.4
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.5 ± 0.2
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.0 ± 0.3
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.5 ± 0.4
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.6 ± 0.5
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.2 ± 1.0
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.3 ± 0.2
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      SY7.5 ± 0.4
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.5 ± 0.3
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.8 ± 0.6
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.6 ± 0.3
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.2 ± 0.5
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.3 ± 1.0
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.2 ± 0.2
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      SY + 7.5% CSM6.4 ± 0.5
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.8 ± 0.3
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.8 ± 0.6
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      5.1 ± 0.9
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      7.2 ± 0.5
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.6 ± 1.3
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      6.3 ± 0.6
      Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      A,B Uppercase letters indicate significant differences among the samples (P < 0.05; n = 30).
      1 0 = very unpleasant; 9 = very pleasant. FFY = full-fat yogurt; SY = skimmed yogurt; CSM = chia seed mucilage.
      The color attribute findings observed by the panelists were in accordance with those observed in the characterization of the different yogurt formulations. Notably, the global acceptance of the sample enriched with 7.5% CSM obtained a lower score probably due to the effect of mucilage on the sample's granularity.

      CONCLUSIONS

      The use of CSM in skimmed yogurts led to significant changes in their nutritional, technological, and sensory characteristics compared with full-fat and skimmed controls. Enriching yogurts with mucilage reduced the degree of syneresis during storage compared with the full-fat and skimmed samples. Moreover, its incorporation improved the nutritional value of the yogurts by increasing their fiber content. The technological characteristics of the yogurts formulated with CSM were enhanced in terms of greater consistency, network structure, firmness, viscosity, and resistance to stress versus skimmed or full-fat yogurts. Storage time positively affected the technological properties of the manufactured yogurts. The sensory evaluation showed that using CSM as a fat replacer in yogurts did not modify the acidity, creaminess, and viscosity of samples, whereas their appearance, color, and granularity played an important role in the products' global acceptance compared with full-fat yogurt. This work provides an interesting alternative for the food industry to reduce fat content in dairy products, increase their nutritional value, and improve the technological features of skimmed yogurts. Our findings could represent an advance in developing novel nonfat yogurts with equal or better characteristics than full-fat yogurts and with several functional benefits for consumers. However, further studies need to be conducted to reduce the impact of CSM on products' color and sensory acceptance.

      ACKNOWLEDGMENTS

      We did not receive any specific grant for this research from funding agencies in the public, commercial, or not-for-profit sectors. The authors declare that they have no conflicts of interest.

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