INFLUENCE OF WATER ACTIVITY ON STREPTOCOCCUS-DIACETYLACTIS METABOLISM

During the cheese-making process, water activity (a(w)) is one of the essential environmental parameters acting on bacterial growth and meta bolic path-ways. The influence of a(w) on Streptococcus diacetylactis growth and lactic acid production was studied. The specific growth rat e was linearly related to water availability in the milk medium. The c ell behaviour was quite different above and below a(w)=0.95, which can be considered a limiting value. Below this value, the lactic acid pro duction reached 1.4-6.1 mg.g(-1), whereas the specific productivity wa s 2.0-2.6 mg.10(-10) cells .h(-1). Changes in the consumption of lacto se and amino acids during the different growth phases was completely m odified by decreasing the water availability in the medium.