ACID PRODUCTION BY BIFIDOBACTERIA AND YOGURT BACTERIA DURING FERMENTATION AND STORAGE OF MILK

Three species of bifidobacteria, namely Bifidobacterium bifidum, Bifid obacterium longum and Bifidobacterium adolescentis were used in pure c ulture and in combination with yoghurt bacteria (B3 and SBI cultures) for the production of fermented milks. The number of bacteria during f ermentation and the level of acid produced during fermentation and sto rage were assessed using Rogosa's modified selective agar and high per formance liquid chromatography (HPLC). It was found that during fermen tation all bifidobacteria exhibited growth uncoupled from acid product ion. Two of the species examined produced only low levels of acids whe n grown individually and only B. adolescentis produced appreciable amo unts. In mixed cultures, the level of acid was a reflection of the com bination of yoghurt culture and species of Bifidobacterium, and this, observation suggests that there is a degree of influence between the c ultures. During storage, the acid concentration remained quite stable in most samples. The prevention of post-production acidification that normally occurs during storage of yoghurt can be attributed to the pre sence of bifidobacteria, and it could be that acetic acid has a margin ally inhibitory effect on the Lactobacillus and Streptococcus spp. (C) 1996 Academic Press Limited