# COMPARATIVE STUDIES ON INDIGENOUS STARTER CULTURE STRAINS FOR THEIR RATE OF ACID PRODUCTION

• Masud, T. (Animal Sciences Institute, National Agricultural Research Centre) ;
• Sultana, K. (Biology Department, Quaid-e-Azam University) ;
• Kausar, R. (Animal Sciences Institute, National Agricultural Research Centre)
Three strains each of L. bulgaricus and S. thermophilus isolated from indigenous dahi were examined for their rate of acid production and corresponding pH values in skim milk medium incubated at $40^{\circ}C$. No significant increase in titrable acidity or decrease in pH were recorded from initial period up to 2nd hour in both the strains. Following this period, however, there was a continuous increase in titrable acidity and a decrease in pH value in the milk for all the tested strains. Further it was observed that there was a variation among these strains for their acid production rate. High rate of acid production was recorded for the L. bulgaricus as compared to S. thermophilus. The results further, suggested that efforts should be made to select a proper pair of L. bulgaricus and S. thermophilus according to their rate of acid production, at a particular temperature in order to produce a good quality product.