Improving viability of Lactobacillus acidophilus and Bifidobacterium spp. in yogurt

Viability of probiotic bacteria was assessed in yogurt prepared using ruptured or whole cells of yogurt bacteria (Lactobacillus delbrueckii sep. bulgaricus 2515 and Streptococcus thermophilus 2010), and whole cells of probiotic bacteria (Lactobacillus acidophilus 2409 and one species of Bifidobacterium; B. longum 1941, B. pseudolongum 20099, B. infantis 1912, B. bifidum 1900 or B. bifidum 1901). Yogurt bacterial cells were ruptured to release their intracellular beta-galactosidase (beta-gal) and reduce their viable counts to improve the viability of probiotic bacteria. Viable counts of probiotic bacteria after fermentation were 2 log cycles higher in yogurt made with ruptured yogurt bacteria and whole cells of probiotic bacteria and their viability after 6 weeks storage remained above the recommended level of 10(6) cfy g(-1), possibly due to the higher level of beta-gal released as a result of rupture of yogurt bacterial cells. Yogurt made with ruptured cells of yogurt bacteria contained less hydrogen peroxide during fermentation. Ruptured or whole cells of yogurt bacteria produced similar levels of acetaldehyde. Thus, with the approach outlined in this study, viability of probiotic bacteria could be improved without compromising the flavour of the product. (C) 1997 Elsevier Science Ltd. All rights reserved.