The Combined Effect of Fortification of Media with Peptone and Control of Acidity on the Growth of Lactic Acid Bacteria

Abstract

The present work was carried out to investigate the combined effect of fortification of media with 1% peptone under control of culture acidity on the growth rate of Lactococcus lactis subsplactis , Lactococcus lactis subsp cremoris and Lactobacillus casei in sterilized skim milk incubated at 34°C. The obtained results indicated that:Lactococcus lactis subsp lactis grow in sterilized skim milk resulted in coagulation of milk after 12 th hour of incubation, and was reached plate count of 28x10 6 CFU/ml.When the same strain grown in sterilized milk supplemented with 1% peptone under control of culture acidity no coagulation was observed up to the end of incubation period after 28 th hour at 34°C, and it reached a plate count of 70x10 6 CFU/ml at the end of the exponential phase after 12 th hour of incubation Cessation of growth in the culture started the stationary phase after 24th hour of incubation. The effect of added 1% peptone to sterilized skim milk under control of culture acidity on the colony forming units of Lactococcus lactis subsp cremoris, indicated that control sample grown in sterilized skim milk reached count of 55x10 6 CFU/ml after 12 th hour of incubation. The corresponding values for Lactococcus lactis subsp cremoris grow with medium supplementation and control of culture acidity reached a plate count of 20x10 7 CFU/ml after 24 th hour of incubation.When Lactobacillus casei grow in sterilized skim milk incubated at 34°C with medium supplementation with 1% peptone under control of culture acidity, the population density was several times higher in culture supplemented with peptone under control of culture acidity reached a population density of 17x10 7 CFU/ml, while only 23x10 6 CFU/ml were recorded by the same strain being grown as a control after 24 th hour of incubation.