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

• Published in: International dairy journal 2010-10, Vol.20 (10), p.665-672
• Main Authors: Michael, Minto, Phebus, Randall K., Schmidt, Karen A.
• Format: Article
• Language: English
• Subjects: Acidity; Allium cepa; application rate; cysteine; food additives; hydrochloric acid; lactic fermentation; Lactobacillus delbrueckii subsp. bulgaricus; natural additives; plant extracts; plate count; redox potential; skim milk; starter cultures; Streptococcus thermophilus; syneresis; titratable acidity; viability; yogurt
• ISSN: 0958-6946; 1879-0143
• DOI: 10.1016/j.idairyj.2010.03.005

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.