Growth of Lactococcus lactis subsp lactis in Milk Under Control of Culture Acidity

Abstract

The effect of control of culture acidity on growth kinetics of one homofermentative strains of lactic acid bacteria, namely., Lactococcus lactis subsp lactis was evaluated. The bacterial growth was estimated on the base of colony forming units, developed titratable acidity and incubation time .Sterilized skim milk was used as a medium with incubation at 34°C.Sampling had been carried out at zero time and each 2 hours intervals. After each sampling, a calculated volume of a liquid of 0.1 N sodium hydroxide was added to the culture to adjust the acidity of the remaining volume of the cultures to its initial value at zero time. The obtained results indicated that:1-When Lactococcus lactis subsp lactis grown under control of culture acidity lag phase was not observed.2-Significant effect of acidity control was noticed on the growth rate. Exponential phase of growth was between 2 ed and 12 th hour of incubation. However, the same culture being grown with control of culture acidity the exponential phase of growth was at interval of time from zero up to 24 th hour of incubation. 3-The maximum cell population in case of the control sample was 124 x 10 5 CFU /ml after 12 hours of incubation. The corresponding values when growth was under control of culture acidity was by a maximum cell population of 35x10 6 CFU/ml after 32 hour of incubation.

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