Differences in the growth, acidification, and proteolytic activities of Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus, and Streptococcus thermophilus in camel and cow milk fermentation

This study investigates low-fat camel milk and cow milk fermentation behavior by Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus, and Streptococcus thermophilus at 28, 35, and 42 °C. Bacterial counts, titratable acidity (TA%), pH, lactose, lactic acid, and proteolysis were followed for 96 h. Temperature and bacteria highly affected all these parameters (p < 0.001) while milk type affected bacterial counts and degree of proteolysis and lactose (p < 0.001), pH, and lactic acid (p < 0.01) but did not affect TA (%). Fermented camel and cow milk products showed similar negative correlations between TA (%) and pH suggesting comparable buffering capacities. In both fermented products, the behavior of L. helveticus was more comparable to that of S. thermophilus than L. bulgaricus. Principal component analysis (PCA) showed a negative correlation between bacterial growth and the degree of proteolysis. The results of this study provided insights into the complex dynamics of bacterial interactions with different milk substrates.