Enhancement of Functional Characteristics of Mixed Lactic Culture Producing Nisin Z and Exopolysaccharides During Continuous Prefermentation of Milk with Immobilized Cells

Populations in gel beads (closed symbols) and prefermented milk (open symbols) of Lactococcus lactis ssp. cremoris ATCC19257 (□, ■), estimated by quantitative PCR, Lactococcus lactis ssp. lactis biovar. diacetylactis UL719 (○, ●) and Lactobacillus rhamnosus RW-9595M (◊, ♦), determined by plate counts, during continuous immobilized cell culture at different temperatures. For prefermented milk, data with more than a 1-d interval corresponded to weekend interruptions. The dashed lines correspond to the effects of age of prefermentation shown on L. lactis ssp. cremoris ATCC19257 (● ● ● ●) and Lb. rhamnosus RW-9595M (—) cell counts predicted by the regression model for a temperature of 31°C. Bars represent standard deviations calculated from triplicate analyses.

Populations of Lactococcus lactis ssp. cremoris ATCC19257 (□), estimated by quantitative PCR, Lactococcus lactis ssp. lactis biovar. diacetylactis UL719 (●), and Lactobacillus rhamnosus RW-9595M (◊), determined by plate counts, in fermented milks after a 22-h incubation of milks prefermented at different temperatures. Data with more than a 1-d interval corresponded to weekend interruptions. The lines correspond to the effects of age of prefermentation on L. lactis ssp. cremoris ATCC19257 (dotted line) and Lb. rhamnosus RW-9595M (dashed line) cell counts predicted by the regression model for a temperature of 31°C. Bars represent the standard deviations calculated from triplicate analyses.

Change of pH during a 22-h batch incubation of prefermented milks produced at different temperatures and different ages of fermentation. Bars represent the standard deviations calculated from 3 repetitions.

Nisin Z concentration in fermented milks after 22-h incubation of prefermented milk produced at different ages and temperatures. Bars represent standard deviations calculated from analyses of 3 samples.

Exopolysaccharide (EPS) concentration in fermented milks after a 22-h incubation of prefermented milk produced at different ages and temperatures. The dashed lines show the EPS concentration in fermented milks predicted by the regression model for different ages of prefermentation and temperature. Bars represent the standard deviations calculated from analysis of 3 samples.

Sensitivity to nisin Z of Lactobacillus rhamnosus RW-9595M produced during control free-cell batch culture in de Man, Rogosa, Sharpe broth (□), in prefermented milks harvested at d 1 (▵) and d 22 (◊; S0) and after 3, 6, 7, and 8 subcultures of cells from prefermented milk harvested at d 22 (◊; dashed lines, S3, S6, S7, and S8). Bars represent standard deviations calculated from 3 repetitions.

Acidifying capacity of prefermented milk samples harvested at d 22, at a temperature incubation of 30 (▴) and 45°C (♦) and control cultures of Lactococcus lactis ssp. lactis biovar. diacetylactis UL719 at 30°C (●) and Lactobacillus rhamnosus RW-9595M at 45°C (■). Error bars represent duplicate experiments.