reduc-Influence of sustainable packaging material and packaging conditions on physicochemical, microbiological, and sensorial properties of cheeses*

The aim of this study was to evaluate the influence of different packaging materials [standard foil: BOPP (biaxially oriented polypropylene)/PET (polyester)/ PE (polyethylene) for upper layer, and APET (poly-ethylene terephthalate)/PE for bottom layer; foil 1: PP (polypropylene)/PET/PE/EVOH (ethylene-vinyl alcohol copolymer)/PE upper layer, and PP/PE/EVOH/ PE bottom layer; foil 2: PP/PET/PE/EVOH/PE upper layer, and PA (polyamide)/EVOH/PE bottom layer; foil 3: PP/PET/PE upper layer, and PA/EVOH/PE bottom layer; foil 4: PP/PET/PE upper layer, and PA/ PE bottom layer; foil 5: PP upper layer, and PP/PP bottom layer] on the quality of 3 different ripening ren-net cheeses packed under different modified atmosphere (MAP) conditions as reflected in particular physico-chemical, microbiological, and sensorial changes. The changes were monitored during a period of 90 d of storage at 2°C or 8°C. For Gouda cheese, CO 2 content of the headspace of the packages was in the range 35 to 45%, whereas for Maasdamer and Sielski Klasyczny cheeses it was 55 to 65%. Three-way ANOVA showed that the foil type influenced the moisture content of Gouda cheese stored for 90 d at 2°C and for Sielski Klasyczny cheese at 8°C, whereas the moisture content was not dependent on MAP conditions during storage. Moreover, the foil type had a significant effect on free fatty acid changes for Gouda and Sielski Klasyczny cheeses stored at 2°C for 90 d. Sensory attributes changed significantly over storage time at 2°C for all studied cheeses as affected by foil type, whereas there was no effect of MAP conditions. In general, the cheeses packed in standard foil and foil 4 were characterized by the highest values of mean sensory attributes. Time was the most significant

ing packaging waste along the production chain, and the environmental footprint of packaging is included in the assessment of the Dairy Product Environmental Footprint.The Green Deal recommends finding new, more sustainable materials and to improving the design of dairy packaging, as well as enhancing reusability, recyclability, and composability of packaging.
The willingness to change the food packaging system also results from changes in consumer awareness.As shown by the European Packaging Preferences 2020 Report (Two Sides, 2022), 70% of consumers are actively taking steps to reduce their use of plastic packaging.
The above-mentioned factors have led to extensive research on packaging materials used in the food industry.Although the use of monofoils would solve many of the issues related to, for example, recycling of food packaging, due to their limitations when used alone, such as gas permeability and susceptibility to welding, their use in cheese packaging is impossible at the moment.Monolayer LDPE films are not suitable for cheese packaging due to their high oxygen transmission rates that accelerate oxidation reactions.Therefore, multilayer films made of polyamide, polyethylene terephthalate, or polyvinylidene chloride are coextruded or laminated with LDPE to provide a good oxygen barrier (Robertson, 2006).These multilayer films are widely used not only for cheese packaging but for other food products, such as chicken breast fillets (Pettersen et al., 2004) and mussel meat (Bindu et al., 2004).Barrier properties for different multilayer packaging were extensively discussed by Lange and Wyser (2003).
The barrier solutions presently available on the market all have their drawbacks, such as cost, water sensitivity, opacity, or perceived environmental bad will.At the same time there is a trend to use more plastic-based packaging materials for different applications, such as replacements for metal and glass containers.This situation has stimulated the industry to provide new, more efficient barrier solutions.These innovations go along 5 major lines: (1) thin, transparent vacuum-deposited coatings; (2) new barrier polymers as discrete layers; (3) blends of barrier polymers and standard polymers; (4) organic barrier coatings; and (5) nanocomposite materials (Lange and Wyser, 2003).
Any innovation using thinner packaging has to be suitably designed to minimize CO 2 loss, which would shorten the life of the product (Alam and Goyal, 2011;Rodriguez-Aguilera et al., 2011;Jalilzadeh et al., 2015;Karaman et al., 2015).In recent years, the cheese market has seen an increase in the market share of packaged cheeses, such as those cut into slices, small blocks, or grated.Such treatments are primarily aimed at increasing the competitiveness of the offered products by adapting to the growing needs of the consumers.In contrast, food distributors' share in the value of food products sold, including cheeses, has increased sharply in recent decades, mainly among retail chains.Very often, they demand from food producers new, innovative methods of packaging that could contribute to extending the shelf life of the product.Consumers' demands must not be omitted, as they expect the product to be stored in the refrigerator for 5 to 7 d after purchase and opening.
One method of preserving the quality of packaged cheeses with an extended use-by date is modified atmosphere packaging (MAP) technology.Its main advantage is the extension of product shelf life, which affects the economy of production, storage, and distribution.It also enables the implementation of a packing system using automatic lines and facilitates the separation of sliced product, which in turn is convenient for the consumer (Sarantópoulos and Soler, 1988).However, the use of MAP technology is also related to investment cost (purchase of new equipment) and implementation costs.The potential of MAP for extending commercial life of cheeses has been clearly demonstrated, although packaging conditions are dependent on the type of cheese, the starter used during manufacturing, and storage conditions, among other important parameters (Gammariello et al., 2009).
The gases normally used for cheese MAP include carbon dioxide (CO 2 ) and nitrogen (N 2 ; Olarte et al., 2001).Generally, the longer shelf life of MAP cheese is due to the inhibition effect of CO 2 on the growth of many spoilage microorganisms (Fedio et al., 1994;Maniar et al., 1994;Alves et al., 1996;Romani et al., 2002).Combined with high barrier packaging film, CO 2 has proven to be a particularly effective preserving agent (Chen and Hotchkiss, 1993).The literature data on the influence of CO 2 on taste and aroma of cheeses are contradictory.Although gas mixtures comprising carbon dioxide (CO 2 ), oxygen (O 2 ), and nitrogen (N 2 ) can be used for protective atmosphere packaging of cheese, several authors have reported how the exclusive use or high percentages of CO 2 may have detrimental effects on the aroma and taste of various cheeses, such as Cameros cheese (Olarte et al., 2001), Cottage cheese (Scott and Smith, 1971), Parmigiano Reggiano cheese (Romani et al., 1999(Romani et al., , 2002)), Samsø cheese (Juric et al., 2003), and Taleggio cheese (Piergiovanni et al., 1993).Conversely, other researchers have reported that the use of high levels of CO 2 does not seem to affect the sensory characteristics of cheese, such as Cottage cheese (Maniar et al., 1994;Mannheim and Soffer, 1996), Mozzarella cheese (Eliot et al., 1998), and Anthotyros cheese (Arvanitoyannis et al., 2011).In general, the aroma and taste of MAP cheeses depends on CO 2 concentration used, packaging type, and product type  (Eliot et al., 1998;Gammariello et al., 2009;Olivares et al., 2012).To be considered economical as well as attractive enough from the consumers' perspective, MAP technology must be optimized for a specific product.It is crucial to determine the following parameters: initial product quality, gas mixture specificity, packaging equipment performance, packaging properties, and temperature control (Alves et al., 1996).
The data on application of thinner packaging materials on sliced cheeses in MAP conditions are very limited and centered around MAP conditions rather than the type of foil used.Most such studies have been carried out in laboratory settings, which might be problematic for transferring to industrial circumstances.A change of packaging material requires extensive research to determine the proper packaging material for the particular cheese type.In the decision-making process on packaging type, cheese producers should also consider such factors as weldability, foil compatibility with the packaging machine, ease of opening, ease of printing, and more.The main objective of the present study was to evaluate the influence of sustainable packaging materials (thinner than standard foil) and MAP conditions on the quality of 3 different cheese types: Gouda (Dutch-type cheese), Maasdamer (Swiss-type cheese), and Sielski Klasyczny (Dutch-Swiss-type cheese).The changes were monitored during a period of 90 d.The rates of changes in physicochemical, microbiological, and sensory characteristics of the cheeses were monitored for cheeses stored at 2 and 8°C to mimic the storage conditions applied to the product during storage.

Experimental Design and Statistical Analysis
Three sliced cheeses-Gouda, Maasdamer, and Sielski Klasyczny (Hochland Sp. z o.o., Poland)-were packed in 6 different packaging materials: 1 standard and 5 experimental (Table 1).Gouda and Maasdamer were selected as representative of 2 different production approaches, Dutch-type and Swiss-type technology, whereas Sielski Klasyczny was produced according to Dutch-Swiss technology.These types of cheese are the most popular variants purchased and consumed in Poland.The cheeses were produced and packed at industrial scale by Hochland Sp. z o.o.(Kaźmierz, Poland).After brining, the cheeses were packed in polyamide (PA)/polyethylene (PE) bags.The dimensions of the cheese blocks were 100 × 500 × 300 cm.Then, the cheeses were ripened for 6 wk for Gouda and Sielski Klasyczny (Dutch and Dutch-Swiss-type cheeses, respectively) and 7 wk in the case of the Swiss-type cheese, Maasdamer.After their respective ripening periods the cheese blocks were cut into slices.For standard packaging (control cheese) one modified atmosphere (CO 2 :N 2 ) was applied (Gouda: 40:60; Maasdamer and Sielski Klasyczny: 60:40), and for each experimental packaging 3 different conditions were applied (Gouda: 35:65,40:60,and 45:55;Maasdamer and Sielski Klasyczny: 55:45,60:40,and 65:35).The cheeses were tested after 7, 30, 60, and 90 d from packaging.Different storage temperatures were applied.Directly after receival, the cheeses in individual packages were placed in refrigerators (air gas composition) and stored at 2 and 8°C (temperature setpoint limits in the refrigerator).The experimental layout is presented in Table 2.
The Kruskal-Wallis test (Statistica software, version 13.1, StatSoft Inc., Tulsa, OK) was used to determine the influence of selected factors on the measured values describing the quality at a given time point of cheese storage.To determine the significance of the influence of time on the measured quantities, a repeated measures ANOVA was conducted.To determine the effect of 3 factors (foil, MAP, time) and 2 factors (foil, MAP) on moisture, pH, free fatty acids (FFA), color parameters (L*, a*, b*), and sensory attributes, including their interactions, multiway ANOVA was used.Statistical analyses were performed, with the significance level of P = 0.05, using the statistical procedures of the Mat-lab2020a package (MathWorks).

Chemical and Instrumental Analyses
For all analytical purposes, except for color measurement, the cheese samples were grated using a cheese grater (Santos type 02, Lyon, France) equipped with a disk with 3-mm-diameter holes.The cheese samples were analyzed for protein content (total nitrogen × 6.38) using the Kjeldahl methods (AOAC, 2007;method 2001.14, 33.7.12A) and fat content using the Schmid-Bondzyński-Ratzlaff method (ISO, 2004;ISO 1735:2004, IDF 5:2004).Moisture was determined gravimetrically by drying 2 g of cheese in a forced-air oven (FD 53, Binder, Tuttlingen, Germany) at 102°C for 24 h (AOAC, 2007;33.2.44, 990.20).The pH of cheese was determined using a Beckman ϕ 72 pH meter (Beckman Instruments Inc., Indianapolis, IN) equipped with an electrode InLab SolidsPro pH (Mettler Toledo, Columbus, OH).
The salt content was determined using a FoodScan analyzer (Foss, Hillerod, Denmark).A petri dish (diameter: 90 mm) filled with cheese shavings was placed in the chamber of the FoodScan.The measurement was performed with the ISIscan software (Foss) using the appropriate application (full-fat cheese).Before starting the measurements, the device was calibrated using a disk dedicated for this purpose.
Cheeses were analyzed for FFA according to the extraction-titration method (Deeth and Fitz-Gerald, 1976).

Color
Color parameters were determined using the CIELAB L* a* b* color system with a CM-3500d spectrophotometer (Konica Minolta, Japan).Spectrophotometry in the visible light range (400-700 nm) was used to register the spectrum.Reflectance was measured by placing the measurement sample on the measurement diaphragm mask (CM-A122) with a measurement field diameter of 8 mm so that the measurement field of the diaphragm was completely covered.The surface of the sample was illuminated by diffusion light at an angle of 8° (d/8) relative to the surface of the tested material.The D65 illuminant and a colorimetric observer with a field of view of 10° were used in the color measurements.Color parameters were determined using the CIELAB L* a* b* color system.Measurements were made after the apparatus was calibrated on a white standard (L* = 96.79,a* = −0.08,b* = −0.16)and a black pattern (L* = 0.02, a* = −0.03,b* = −0.01).
The measurement results were recorded and analyzed by the CM-S100w SpectraMagicTM NX Lite ver.2.3.

Sensory Analysis
The sensory analysis was conducted by a trained panel consisting of 7 panelists with at least 120 h experience in sensory evaluation of dairy products.The following attributes were scored.In terms of aroma: milky (only Gouda), nutty (only Maasdamer and Sielski Klasyczny), lipolytic, and foreign.In terms of taste: milky (only Gouda), nutty (only Maasdamer and Sielski Klasyczny), cooked, lipolytic, salty, acid, bitter, and foreign.A 5-point scale was used, where 5 represented the most desired intensity of the attribute and 1 the least desired.Desirability did not correspond in all cases to intensity of given attribute; for instance, in the case of milky flavor the most desired and the most intense was 5, whereas in the case of bitter taste the most desired was 5, which corresponded to lack of bitter taste.The results are expressed as the mean value of the scores of all attributes for a given sample, unless otherwise stated.At each sampling day, cheese packs were aseptically opened and 10-g samples were taken, followed by addition of 90 mL (first dilution) of peptone water (Merck, Warsaw, Poland).The samples were blended for 120 s (under fixed speed: 8 strokes/s) using a laboratory blender BagMixer 400W (Interscience, St. Nom la Bretéeche, France).
The numbers of S. aureus and E. coli were determined using, respectively, the TEMPO STA and EC selective tests compatible with the TEMPO system (bio-Mérieux, Marcy l'Etoile, France).The TEMPO tests require hydration of the medium by adding 3 mL of sterile water.After adding 1 mL of the first dilution of a cheese sample, a scan of the tests was made.Prepared samples were placed in the TEMPO Filler component.After reading the data and closing the cards, the stands containing filled cards were transferred to the incubators (ICP500, Memmert GmbH + Co. KG, Schwabach, Germany) and stored at 37°C for 24 h.After the incubation period, the cards were placed in a TEMPO Reader station, where the data were saved.The last stage of work was validation of the obtained results.
For determination of the presence or absence of L. monocytogenes, a BacTrac 4300 system (SY-LAB, Neupurkersdorf, Austria), based on proprietary patented impedance splitting technology, was used.Measurements were performed aerobically in 10-mL reusable measuring cells at 37°C for 48 h at 10-min intervals.Impedance splitting technology refers to the fact that 2 independent parameters are measured simultaneously: the impedance of the medium (M-value) and the impedance of the electrochemical bilayer on the surface of the electrodes (E-value).The relative change in impedance in time is registered with reference to the value at the beginning of the measurement.Time when a rising growth curve surpasses a defined threshold is registered as impedance detection time.A BiMedia 404A for L. monocytogenes was used for the impedance experiments.The medium was sterilized at 121°C for 15 min.The selective medium and first dilution of the cheese samples were aseptically distributed to the measuring cells (10 mL), each sample in 3 replicates, and incubated at 37°C for 24 h in the BacTrac thermostatic blocks.A 5% relative change in impedance of the Evalue was the threshold used for the tests.

Influence of Packaging Material
To eliminate the influence of time, a 2-factor ANOVA was carried out at d 30, 60, and 90, which revealed significant effects of foil (only experimental foils) on the composition, color parameters, and sensory attributes for all studied cheeses stored at 2°C and, in most cases, at 8°C (Table 3).No clear trend was found for influence of foil type for tested cheese at specific time intervals (Table 3).For Gouda cheese, the foil had significant influence on sensory attributes at each time period at both temperatures, but only at 2°C for Maasdamer (Table 3).The sensory attributes of Sielski Klasyczny cheese were influenced by foil type only at d 60 (2°C and 8°C) and d 90 of storage at 8°C.In general, from the tested parameters (Table 3), color values were characterized by the lowest sensitivity to changes under the influence of the foil at 8°C (Table 3).
The type of package influenced the moisture content only at 60 d of storage in the case of Gouda and Maasdamer cheeses (Table 4) and at 7 d for Sielski Klasyczny (Table 4) at 2°C.The lowest values for moisture content in these specific intervals were noticed for foil 2 (in case of Gouda) and foil 3 (Maasdamer and Sielski Klasyczny).
The final pH for Gouda cheese stored at 2°C did not differ (P ≥ 0.05) at the last day of storage (d 90) among different packaging tested (Table 4).Small but significant differences in final pH for Maasdamer and Sielski Klasyczny cheeses were detected at d 90 between differently packed samples (Table 4).The starter cultures for Gouda cheese consisted only of Lactococcus lactis ssp.lactis var.diacetylactis, whereas for the production of Maasdamer Propionibacterium freudenreichii species was also used.Sielski Klasyczny cheese was produced with Leuconostoc spec., Lactococcus lactis ssp.lactis var.diacetylactis, and Propionibacterium freudenreichii.The evolution of cheese pH during storage is related to activity of starter culture used and packing conditions.The differences among samples after 30 or 60 d of storage could possibly be affected by different conditions inside the packages resulting from different permeability of the foils, which in turn influenced moisture content.We found significant correlation (data not shown) between pH and moisture content for Gouda cheese at 2°C (−0.5402) and between pH and protein content for Sielski Klasyczny cheese stored at 2°C (0.6112).Gouda cheese has a typical pH value of 5.2 to 5.3, due to the activity of the starter lactic acid bacteria that convert lactose to lactic acid (Wemmenhove et al., 2016); in our study, an average pH value for Gouda cheese was higher, approximately 5.67.According to Düsterhöft et    2017) most modern types of cheeses have a somewhat higher pH than their traditional counterparts; one reason for this change is to obtain better sliceability of the matured cheese (Düsterhöft et al., 2017).No differences were detected (P < 0.05) for FFA content at the last day of storage for all studied cheeses stored at 2°C when comparing cheeses packed in standard foil and experimental foils (Table 4).Many researchers have demonstrated the increase in FFA content during ripening of cheeses (Woo et al., 1984;Nájera et al., 1994;Contarini and Toppino, 1995;Mallatoua et al., 2003).Mallatou et al. (2003) showed that not all FFA increased at the same rate and, as a result, the FFA composition of Teleme cheeses made with ewe, goat, cow, or a mixture of ewe and goat milk varied considerably over the 180-d ripening period.The percentage of short-chain FFA, including acetic acid (C2-C8), which has a significant effect on the development of the characteristic aroma of the cheese, was increased during the first 60 d of ripening for all types of cheeses.The percentage of medium-chain FFA (C10-C14) de-creased during the same period.Contrary to this, the percentage of long-chain FFA (C16-C18:2) remained quite constant during ripening.
The foil type influenced (P < 0.05) sensory attributes (calculated as mean of all tested attributes) for Gouda and Maasdamer cheese (Table 4), and the difference was detectable already after 30 d of storage at 2°C.In general, the cheese packaged in foils 1, 2, and 5 in the case of Gouda, and foils 1 and 3 in the case of Maasdamer cheese, received the lowest scores in sensory evaluation (Table 4).The influence of foil type was not so clear in the case of Sielski Klasyczny cheese (Table 4).For this cheese, we found no differences (P ≥ 0.05) in mean sensory attributes between the different foils tested (standard foil and the 5 experimental foils).Among cheese samples stored at 2°C (Table 4), Maasdamer and Sielski Klasyczny cheeses packed in foil 4 showed the best characteristics.In the case of Gouda cheese, the packaging made of foils 3 and 4 preserved to the best extents the sensory attributes of the product (Table 4).However, it is worth noting that the pack- Foil S = standard foil; foils 1-5 = experimental foils.For specific compositions, see Table 1.
ages made of foil 3 were rather difficult to open.In general, the cheeses packed in standard foil and foil 4 were characterized by the highest values of mean sensory attributes.Among experimental foils (1-5) the thinnest ones were foil 1 (lid: 10 µm; bottom: 93 µm) and foil 5 (lid: 65 µm; bottom: 85 µm; Table 1).These were also the foils with the lowest O 2 transmission rates (Table 1).The compositions of the upper parts (lid) of foils 3 and 4 were identical [polypropylene (PP)/polyester (PET)/PE], so the differences must result from the properties of the bottom parts: PA/ethylene-vinyl alcohol copolymer (EVOH)/PE and PA/PE for foils 3 and 4, respectively.Among the properties of PP, the following should be reported: semi-rigid, translucent, good chemical resistance, tough, good fatigue resistance, integral hinge property, and good heat resistance; whereas PET has good chemical resistance and does not react with foods and liquids.Also PE is characterized by many properties desirable for packaging, such as semirigidity, translucency, toughness, weatherproofness, good chemical resistance, low water absorption, ease of processing by most methods, and low cost.Used in the bottom foil, polyamides are widely used for demanding applications in the packaging field due to their unique combination of mechanical strength, but also for their high heat distortion temperature; high flexibility and toughness; the good barrier to oxygen, chemicals, and aromatic substances that they provide; as well as their high transparency and thermoformability.The application of EVOH in foil 3 (as compared with foil 4) resulted in better sensory attributes of packed cheeses compared with other foils, which may result from the many positive attributes of this foil, such as excellent oxygen barrier, high transparency, flavor barrier, high rigidity, and easier processability-lower back pressure.Differences in color parameters occurred for all studied cheeses between the different foils used (Table 5); however, no trend was detectable.In general, in the case of Gouda cheese the differences in L*-value were detected (P < 0.05) starting from d 30 of storage.In the cases of Maasdamer and Sielski Klasyczny, the differences were detectable (P < 0.05) already at d 7, which may result from variations among the samples rather than the type of foil used.
An important factor influencing the selected quality characteristics of the cheese, apart from the composition of the modified atmosphere, is selection of the appropriate packaging material.According to scientific reports, the properties of barrier foils (i.e., thickness) had a significant effect on the water content and hardness of the Tvarog cheese (Polish acid-coagulated white, fresh cheese) stored under refrigerated conditions (Dmytrów et al., 2007).When PE/EVOH/PA foils of various thicknesses were used in the study (Dmytrów et al., 2007), no unequivocal influence of packaging on the fat content, titratable acidity, pH, or sensory properties of the experimental Tvarog cheese was detected.In another study, Dmytrów et al. (2011) carried out an experiment aimed at investigating the effects of MAP (90:10 N 2 : CO 2 ) used with polylactic acid (PLA) packages compared with MAP used with PA/ PE packaging material on Tvarog cheese.Three MAP package variations were evaluated.The film materials tested were PLA, metalized PLA, and PA/PE films.All the packages inhibited fat oxidation but not the transformation of fatty acids into conjugated diene and triene structures.The most effective protection against unfavorable changes in the products was found with the PA/PE packaging material.Pluta et al. (2013), when examining the influence of MAP packaging (different proportions of gases and different thickness of packaging materials) on the quality characteristics of sliced Swiss cheese, found no correlation between the type of foil and the microbiological quality of the product.
No data have been found in the literature to unequivocally indicate the relationship between a specific packaging material and the quality characteristics of different types of cheese.Therefore, it is important to study suggested packaging materials to determine the relationship between the method of cheese packaging and the quality of the final product.

Influence of MAP
Two-way ANOVA revealed a significant influence of different MAP conditions applied (Table 3) in each studied time interval; however, the sensory attributes were not affected by MAP conditions for all studied cheeses after 30 and 60 d of storage for the cheeses stored at 2°C.The same tendency was observed in the cheeses stored at 8°C but only after 30 d of storage (Table 3).Additionally, in Maasdamer cheese, MAP conditions did not influence mean sensory attributes at any studied period of time or any temperature.
In our case, the maximum CO 2 concentration was 65% for Maasdamer and Sielski Klasyczny, and 45% for Gouda cheese.Such conditions were chosen based on the experience and observations of the employees of Hochland Polska Sp. z o.o., the cheese producer.In general, for the cheeses produced with propionic bacteria or gas-producing bacteria, a higher percentage of CO 2 is recommended.
The data reported in the literature clearly show that the effect of the gas mixtures used for packaging is closely related to the composition of the packaged cheese.Gas mixtures with high N 2 percentages have been proved to be more suitable when dealing with semi-hard or hard-type cheeses (Romani et al., 2002;Juric et al., 2003).An atmosphere made of 100% CO 2 is often suggested by gas suppliers as the best atmosphere composition for cheese packaging (Favati et al., 2007).
Several authors (Floros et al., 2000;Papaioannou et al., 2007;Conte et al., 2009;Gammariello et al., 2009) have demonstrated the potential of MAP for extending the shelf life of dairy products, including cheese.Those authors summarized that success in cheese packaging is dependent on several important parameters, such as the type of cheese, the use of starter cultures dur- ing production, initial microbial contamination, and storage conditions.The gases normally used for MAP include CO 2 , O 2 , and N 2 .The most important gas from a microbiological point of view is CO 2 , used alone or in mixtures with N 2 or O 2 , which inhibit the growth of many microorganisms, including spoilage bacteria (Daniels et al., 1985).Carbon dioxide effects depend upon its concentration, water activity, pH, number, age and kind of the microorganisms and temperature (Eliot et al., 1998).Different compositions of modified atmospheres have been tested to evaluate effects during cheese storage.Modified atmosphere has preserved sensory qualities of various cheeses and inhibited growth of psychrotrophic bacteria, yeasts, and molds (Fedio et al., 1994;Maniar et al., 1994).Piergiovanni et al. (1993) compared Tallegio cheese packaged under 4 modified atmospheres and stored at 6°C against traditional paper wrapping and found that samples packaged in MAP had satisfactory quality.The MAP caused significant differences in sensory, chemical, and color properties, but not in microbiological analysis.The optimal composition of MAP for cheese preservation varied depending on type of cheese: for instance, 10% CO 2 /90% N 2 for Tallegio or 100% CO 2 for Cottage cheese and sliced Mozzarella cheese (Eliot et al., 1998).
Modified atmosphere is a well-established technique in which the gas composition surrounding a product is altered, resulting in an atmosphere different from that of air (Rodriguez-Aguilera et al., 2011b).The optimal atmosphere composition for each product is created by matching the permeability of the packaging material with the CO 2 production and O 2 consumption rates of the specific product.The packaging material may consist of a polymeric flexible film or an impermeable covering with perforations (Oliveira et al., 1998), this last option being the most suitable for highly respiring products (Silva et al., 1999).In both cases the reliability of MAP depends on rigorous temperature control (Tano et al., 2007).The package for a product to be stored under a given modified atmosphere is designed for a specific constant temperature, which depends on the product itself; however, real-life distribution chains are not stable.A typical logistic chain is characterized by different processes such as sorting, grading, packing, and transport, each with their own typical conditions (Hertog et al., 2007).

Influence of Temperature
The storage temperature did not affect the moisture of the samples during storage.The profiles of moisture changes for cheeses stored at 2°C and 8°C for the 90-d period were almost identical for each type of cheese (Figure 1).
For most of the studied cheeses we found an increase in pH value during storage regardless of storage temperature (Figure 2).The only exception was Maasdamer cheese stored at 2°C, for which the pH decreased (P < 0.05).In general, higher temperature is associated with greater increase in pH.The changes in pH value were the lowest for Maasdamer cheese.In turn, Gouda cheese showed the biggest shift in pH during storage for each temperature variant.It should be noted that CO 2 used in MAP technology dissolves readily in water (1.57g/kg at 100 kPa, 20°C) to produce carbonic acid (H 2 CO 3 ), which increases the acidity of the solution and reduces the pH.This gas is also soluble in lipids and some other organic compounds.The solubility of CO 2 increases with decreasing temperature (Mullan and McDowell, 2011).
Gouda cheese showed the lowest FFA content among all studied cheeses regardless of storage temperature (Figure 3).For Gouda and Maasdamer cheeses we detected no difference in final FFA contents between cheeses stored at 2°C and 8°C; however, the samples of Sielski Klasyczny cheese differed in FFA content at the last day of storage depending on the temperature of storage (Figure 3).
Free fatty acids are precursors for the formation of other flavor compounds, in addition to having a direct influence on cheese flavor.High FFA content may cause further oxidation and lead to development of offensive taste and flavor.Oxidation has been reported in Danboo cheese (25% fat) packed in polyethylene terephthalate trays with an oxygen scavenger for 84 d at 4°C (Holm et al., 2006).
The storage temperature and time of storage had significant effects on sensory attributes of the studied cheeses.The cheeses stored at 8°C were characterized by lower values (Appendix Table A1) of each of the studied attributes when compared with samples stored at 2°C (Appendix Table A2).Among the studied cheeses, Maasdamer preserved its characteristics to the best extent when stored at 8°C, with the highest scores for sensory attributes (the smallest difference between d 7 and 90).Propionic bacteria used in the production of that cheese produce CO 2 , which affects the pH of the cheese (Maasdamer had the lowest pH values among the studied cheeses; Figure 2), acting as natural preserving agent.Some Gouda and Sielski Klasyczny cheeses were not subjected to flavor analysis but only aroma after 60 d of storage at 8°C, as cheeses showed defects such as cowshed aroma, in some cases putrefactive aroma, rendered fat, and water inside the package.In both cases, cheeses packed in foil 4 showed the smallest aroma defects and were subjected to flavor analysis even after 90 d of storage at 8°C.After 90 d of storage at 8°C, most of Gouda and Sielski Klasyczny cheeses were analyzed only for aroma; however, the Gouda cheese samples packaged in foil 4 were subjected to complete analysis, as the cheese did not show any defects that could eliminate it from further analysis.Only Maasdamer cheese was able to maintain relatively high scores for sensory attributes for samples stored at 8°C during the 90-d storage period, regardless of the foil type and MAP conditions.
The increment of temperature during the distribution chain of food products is especially critical for highly respiring products because it could easily lead to anaerobic conditions, which could produce metabolic disorders with off-flavors and off-odors (Rodriguez-Aguilera et al., 2011a) and even constitute a potential health hazard for the consumer.

Influence of Storage Time
Time was the most significant factor influencing the changes in physicochemical and sensory attributes of cheeses stored at 2°C and 8°C (Table 6).The interactions of foil and MAP conditions with time were pronounced only for selected parameters for both storage temperatures.
Based on the results from sensory evaluation of cheese samples, it can be concluded that only the selected thinner foils could guarantee sensory attributes during the declared best-before date (90-d storage time) comparable to those of standard foil (Table 4, Appendix Table A2).As the storage time proceeded, the scores for sensory attributes were lower.
Rodriguez-Aguilera et al. (2011a) studied the packaging of a surface mold-ripened cheese under 2 atmospheres: MAP-A (0% O 2 , 27 ± 6% CO 2 ) and MAP-B  and 8°C).Means (n = 15) were calculated for experimental foils in different modified atmosphere of packaging conditions.For specific compositions of experimental foils, see Table 1.(2 ± 1% O 2 , 19 ± 2% CO 2 ) were studied at 12°C, and the results were compared with a commercial packaging system (wrapped with waxed paper and inserted in a cardboard box).Those authors concluded that time and packaging conditions significantly affected the average values of sensory response, but the interaction of these 2 factors did not have a significant effect.In their study, the interaction of time and packaging conditions significantly affected the pH and moisture content of the cheese (Rodriguez-Aguilera et al., 2011a).

Safety Aspects
Maintaining cheese quality during storage requires protection against dehydration and reduction of undesirable microorganisms, especially pathogens.Microbiological assessment revealed that L. monocytogenes was not detected in all cheese samples; meanwhile the numbers of S. aureus and E. coli were below 10 cfu/g during the whole storage period.It was concluded that the studied cheeses met the microbiological safety criteria defined in EU Regulation 2073/2005(European Commission, 2005).

CONCLUSIONS
The foil type (3-way ANOVA) influenced the moisture content of Gouda cheese stored for a 90-d period at 2°C and for Sielski Klasyczny cheese at 8°C, whereas the moisture content was not dependent on MAP conditions during storage.Moreover, the foil type had a significant effect on FFA changes for Gouda and Sielski Klasyczny cheeses stored at 2°C for 90 d.Sensory attributes changed significantly over storage time at 2°C for all studied cheeses as affected by foil type, but no effect of MAP conditions was detectable.In general, the cheeses packed in standard foil and foil 4 were characterized by the highest values of mean sensory attributes.Time was the most significant factor influencing most changes in physicochemical and sensory attributes of cheeses stored at 2°C and 8°C.Storage temperature did not affect the moisture of samples during storage.In general, we found an increase in the pH value during storage, regardless of storage temperature.It was possible to decrease the thickness of the packaging material from the initial 103/250 µm (standard foil; lid and bottom, respectively) to 98/100 µm (foil 4) without affecting sensory attributes of the product.A 5-point scale was used, where 5 indicated the most desired intensity of the attribute and 1 the least desired.Desirability did not correspond in all cases to intensity of given attribute; i.e., in the case of milky flavor, the most desired and the most intense was 5, whereas, in the case of bitter taste, the most desired was 5, which corresponds to lack of bitter taste.Note that 0 was given for the sample that was not tested due to aroma defects.For the first week after packaging the samples were stored at 2°C, so the 7-d values are for the samples stored at this temperature; after 7 d the samples were placed in a refrigerator with temperature set to 8°C.Foil S = standard foil; foils 1-5 = experimental foils.For specific compositions of experimental foils, see Table 1.A 5-point scale was used, where 5 indicated the most desired intensity of the attribute and 1 the least desired.Desirability did not correspond in all cases to intensity of given attribute; i.e., in the case of milky flavor, the most desired and the most intense was 5, whereas, in the case of bitter taste, the most desired was 5, which corresponds to lack of bitter taste.Note that 0 was given for the sample that was not tested due to aroma defects.Foil S = standard foil; foils 1-5 = experimental foils.For specific compositions of experimental foils, see Table 1.

Table A2 (Continued).
Mean values of descriptors evaluated by sensory panel (n = 7) for different cheese samples (Gouda, Maasdamer, Sielski Klasyczny) packed in different foils and stored at 2°C 1 Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES Table 3. Two-way ANOVA for moisture, pH, free fatty acids (FFA), color parameters (L*, a*, b*) and sensory analysis of modified atmosphere of packaging (MAP) cheeses stored at 2°C and 8°C after 30, 60, and 90 d of storage in experimental foils; see Zulewska et al.:  THINNER PACKAGING MATERIALS FOR RENNET CHEESES thotyros cheese and found that both MAP1 and control samples (cheese packed in air) had very negative effects on sensory qualities.
Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES

Figure 1 .
Figure 1.Changes in moisture content for different cheeses stored at different temperatures (2and 8°C).Means (n = 15) were calculated for experimental foils in different modified atmosphere of packaging conditions.For specific compositions of experimental foils, see Table1.

Figure 2 .
Figure 2. Changes in pH for different cheeses stored at different temperatures (2 and 8°C) in experimental foils.Means (n = 15) were calculated for different foils in different modified atmosphere of packaging conditions.For specific compositions of experimental foils, see Table 1.
Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES

Table 1 .
Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES Compositions of plastic films used to produce packaging: lid and bottom foils 1

Table 3 (Continued). Two
-way ANOVA for moisture, pH, free fatty acids (FFA), color parameters (L*, a*, b*) and sensory analysis of modified atmosphere of packaging (MAP) cheeses stored at 2°C and 8°C after 30, 60, and 90 d of storage in experimental foils; seeTable 1 for details of packaging compositions 1 al. (

Table 4 .
Zulewska et al.:THINNER PACKAGING MATERIALS FOR RENNET CHEESES Mean moisture, pH, free fatty acids (FFA), and sensory attributes (average for all attributes analyzed) of modified atmosphere of packaging (MAP) cheeses stored at 2°C for 90 d, packaged in different foils a-c Means within a column for each examined parameter (moisture, pH, FFA, mean sensory attributes) with different superscripts are different (P < 0.05).1

Table 6 .
Three-way ANOVA for moisture, pH, free fatty acids (FFA), color parameters (L*, a*, b*) and sensory analysis of modified atmosphere of packaging (MAP) cheeses stored

Table A1 .
Mean values of descriptors evaluated by sensory panel (n = 7) for different cheese samples (Gouda, Maasdamer, Sielski Klasyczny) packed in different foils and stored at 8°C 1 Journal of Dairy Science Vol.TBC No. TBC, TBC Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES

Table A1 (
Continued).Mean values of descriptors evaluated by sensory panel (n = 7) for different cheese samples (Gouda, Maasdamer, Sielski Klasyczny) packed in different foils and stored at 8°C 1 Journal of Dairy Science Vol.TBC No. TBC, TBC Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES

Table A2 .
Mean values of descriptors evaluated by sensory panel (n = 7) for different cheese samples (Gouda, Maasdamer, Sielski Klasyczny) packed in different foils and stored at 2°C 1 Journal of Dairy Science Vol.TBC No. TBC, TBC Zulewska et al.: THINNER PACKAGING MATERIALS FOR RENNET CHEESES