Viability of Lactic Acid Bacteria, Antioxidant Activity and In Vitro Inhibition of Angiotensin-I-Converting Enzyme of Lycium barbarum Yogurt

Abstract

Lycium barbarum water extract was co-incubated with milk and starter culture during fermentation followed by refrigerated storage. The changes in viable cell counts (VCC) of yogurt bacteria, post-acidification, proteolytic activity, total phenolic content (TPC), antioxidant activity, angiotensin-I converting enzyme (ACE-I) inhibition activity and sensory evaluation were investigated during refrigerated storage (4 °C) up to 21 days. The VCC of Lactobacillusspp. was higher (p < 0.05) in L. barbarum yogurt than plain yogurt on 0 and 3 days of storage. The VCC of Streptococcus thermophilus in L. barbarum yogurt was higher (p < 0.05) than plain yogurt on the first 6 days of storage. Changes in pH were not different between plain and L. barbarum yogurts during 21 days of storage. However, titratable acidity (TA) was higher in fresh (0 day) L. barbarum yogurt (1.05 %; p < 0.05) than in plain yogurt (0.87 %). Proteolytic activity was higher in L. barbarum yogurt (32.0 ± 2.0 μg/g; p < 0.05) than plain yogurt (25.4 ± 1.1 μg/g) only on day 7 of storage, whereas free amino acids showed the highest value on 0 day (0.16 ± 0.1 and 0.20 ± 0.1 mM leucine equivalent for plain and L. barbarum yogurts, respectively). The presence of L. barbarum increased (p < 0.05) TPC and antioxidant activity in yogurt compared to the absence. However, L. barbarum yogurt did not affect ACE-I inhibitory activity during storage period. The addition of L. barbarum increased sweetness, overall aroma and preference scores of yogurt. In conclusion, L. barbarum can enhance yogurt functional properties with antioxidant activity.