Study on the Effect of Dextrose, Valine, Glycine, Thiamine and Different Tempratures on Growth Rate of Lactobacillus Casei in Milk

In recent years several experimental studies have been carride out about benefical effects of L. casei, one of the probiotic bacteria, on animals and human. The first step for the use of microorganisms in order to producing probiotic milk products is to recognize their growth conditions in milk and effective elements on it. In this research, the effects of dextrose, glycine, thiamine and different tempratures on growth rate of L. casei in milk have been studied. A series of 38, 40, 42 and 440C incubators were used to choose the best incubation temprature. The acidity of milk samples were measured as the growth index of the microoganism prior and during incubation. The amounts of 0, 5, 10 and 15ppm of vitamin B1; 0, 0.4, 0.6, 0.8 and 1 percent of dextrose; 0, 30, 60, 90 and 120ppm of valine and glycine were used to evalute their effects on the growth rate of L. casei and acidity of milk samples were measured in 0, 1, 2, 3, 4 and 5 hourse of incubation at 420C. The increase of acidity rate at 440C and 420C was significantly higher than other tempratures (p< 0.05). The addition of dextrose, valine, glycine had no significant effect on the acidity rate of the milk samples (p<0.05). Although the addition of thiamine did not have significant effect on the acidity but it improved the ability of enzyme and gas production.