Fresh-cheesemilk formulation fermented by a combination of freeze-dried citrate-positive cultures and exopolysaccharide-producing lactobacilli with liquid lactococcal starters

Milk formulation (4% fat and 5% protein) prepared to simulate fresh cheese production was inoculated with: (1) 10(7) cfu mL(-1) of fresh liquid starters of Lactococcus lactis ssp. lactis T1 and Lc. lactis ssp. crenioris T2, (2) a freeze-dried exopolysaccharide-producing (EPS) strain of Lactobacillus rhamnosus RW-9595M, and (3) freeze-dried Leuconostoc cremoris LM057 or Lc. lactis ssp. lactis var. diacetylactis MD089 strains. The effect of inoculation rate of the freeze-dried starters (between 106 and 107 cfu mL-1) and incubation temperature (between 23.5 and 36.5 degrees C) on evolution of pH and the various populations during fermentation was examined. Texture (apparent viscosity, syneresis potential) and chemical composition (diacetyl, acetaldehyde) of the fermented milks were also determined. Milk was incubated until a pH of 4.6 was obtained, which required between 6 and 10 h depending on temperature. In the range of inoculation levels used, there was no significant effect of the presence of lactobacilli, Ln. crenioris or Lc. lactis ssp. lactis var. diacetilactis on the growth of the lactococci. There was a direct correlation between the inoculation rates of the freeze-dried cultures and their final populations in the fermented milks. The growth of the cultures were also affected by temperature, Ln. cremoris growing less as incubation temperature increased, while the opposite was noted with Lb. rhamnosus. The apparent viscosity of the fermented milk was significantly affected by incubation temperature, but there was no correlation between apparent viscosity and the final population in lactobacilli. Of the three variables studied, the highest correlation with diacetyl content was obtained with the inoculation level of the Leuconostoc strain. (c) 2006 Elsevier Ltd. All rights reserved.