LAUSR

Understanding the effect of pH on the growth of Lactobacillus delbrueckii subsp. Bulgaricus is essential for controlling starters production. Previous studies suggested that L. bulgaricus Q7 in uncontrolled pH cultures showed better acidic activity in milk compared with that in controlled pH cultures. The present study aimed to elucidate the effect of uncontrolled and controlled pH cultures on the growth of L. bulgaricus Q7. The growth kinetics, physiological state, amino acid consumption and necessary profiles of L. bulgaricus Q7 were investigated in the complete chemically defined medium under uncontrolled and controlled pH cultures circumstances respectively. The results showed that the average growth rate and final biomass of L. bulgaricus Q7 were higher in uncontrolled pH cultures than those in controlled pH cultures. Furthermore, the high intracellular pH led to the high average growth rate and final biomass in uncontrolled pH cultures. The H+-ATPase activity, ATP concentration, ratio of NADH/NAD+, NH3 concentration, consumption and necessary profiles of amino acid led to high intracellular pH in uncontrolled pH cultures. Such results might benefit industrial starter producers and fermented-product manufacturers by allowing them to formulate new strategies to enhance biomass of L. bulgaricus and better control the quality of starters.