Physicochemical, microbiological, and sensory properties of low-lactose yogurt using Streptococcus thermophilus with high & beta;-galactosidase activity

BACKGROUNDLactose maldigestion or intolerance affects a large number of individuals worldwide. If lactose is hydrolyzed by the beta-galactosidase enzyme during the fermentation process, lactose-intolerant individuals can consume milk products without experiencing diarrhea, flatulence, or other symptoms. RESULTS AND CONCLUSIONWe isolated and characterized Streptococcus thermophilus, which exhibits high & beta;-galactosidase activity. This was then used as a starter culture with Lactobacillus delbrueckii subsp. bulgaricus in yogurt to determine the effects of different starter ratios and fermentation temperatures on its organoleptic and physical properties. The beta-galactosidase activity of the isolated strain was 2.60 units mg(-1). The optimal temperature was 42 degrees C for St. thermophilus to acidify yogurt faster than at other temperatures and it was effective in hydrolyzing the lactose in the media and yogurt. The lactic acid bacteria (LAB) population in 37 degrees C fermented yogurt was higher than in the other samples, but the starters St. thermophilus and Lb. bulgaricus with a ratio of 2:1 used lactose more effectively than other sample ratios. The lactose content decreased significantly at 37 degrees C, where it was similar to 50% hydrolyzed. The acceptability of the sensory properties of yogurt was unaffected by relative lower fermentation temperatures (30 and 37 degrees C), despite using different ratios of St. thermophilus and Lb. bulgaricus as starter cultures. (c) 2023 Society of Chemical Industry.

Automated summary

This study isolated and characterized Streptococcus thermophilus with high β-galactosidase activity and used it as a starter culture with Lactobacillus delbrueckii subsp. bulgaricus to make yogurt. The optimal fermentation ratio and temperature were found to be 2:1 and 42℃, respectively, leading to better organoleptic and physical properties of the yogurt. Higher lactobacilli population was observed in yogurt fermented at 37℃, and yogurt with a ratio of 2:1 starter cultures utilized lactose more effectively. The sensory properties of the yogurt remained unaffected at lower fermentation temperatures of 30 and 37℃.