Impact of a plant extract on the viability of Lactobacillus delbrueckii ssp bulgaricus and Streptococcus thermophilus in nonfat yogurt

The effect of a plant extract (prepared from olive, garlic, onion and citrus with sodium acetate as a carrier) on the viability of yogurt starter cultures was studied. Nonfat yogurt was prepared with various levels of supplements: plant extract (0, 0.5 or 1.0%, w/v) or L-cysteine HCl (0.014 or 0.028%, w/w). Microbial and physicochemical analyses were conducted weekly for 50 days. Fermentation time increased for supplemented yogurts compared with the non-supplemented yogurt. Lactobacillus bulgaricus counts in supplemented yogurts were >6 log cfu mL(-1) for a longer time (7-21 days) compared with the non-supplemented yogurt. Streptococcus thermophilus counts in all yogurts were > 6 log cfu mL(-1) throughout the storage. Overall, redox potential and titratable acidity of yogurts on day 50 were greater compared with day 1, but pH and syneresis were less. Plant extract at 0.5% enhanced L bulgaricus viability in nonfat yogurt while least affecting the physicochemical characteristics. Published by Elsevier Ltd.