Physicochemical analysis, proteolysis activity and exopolysaccharides production of herbal yogurt fortified with plant extracts

Abstract

Abstract Yogurt production with starter culture at 41 °C in the presence of plant water extracts ( Momordica grosvenori , Psidium guajava , Lycium barbarum or Garcinia mangostana ) were studied to examine the effects on acidification, physicochemical properties, microbial growth, proteolytic activity, and exopolysaccharide (EPS) content. All plant-based yogurt reached a pH of 4.5 faster (300–330 min) than plain-yogurt (360 min). All plant water extracts stimulated Lactobacillus spp. (∼7.4 log 10 CFU/mL) and Streptococcus thermophilus (8.20–8.50 log 10 CFU/mL) growth except for G. mangostana which marginally inhibited Lactobacillus spp. growth (7.21 log 10 CFU/mL). M. grosvenori, L. barbarum, and G. mangonstana were significantly affected proteolysis of milk proteins (46.2 ± 0.8, 39.9 ± 0.5, & 35.8 ± 0.1 µg/mL; respectively) compared to plain-yogurt (26.3 ± 0.4 µg/mL). The presence of G. mangostana and L. barbarum resulted in an increase ( p < 0.05) of total solids content (∼15.0%) and water holding capacity in yogurt (28.1 ± 1.2 & 26.5 ± 0.3%; respectively; p < 0.05). In addition, M. grosvenori water extract enhanced ( p < 0.05) syneresis of yogurt (1.78 ± 0.30%). L. barbarum yogurt showed the highest EPS concentration (220.9 ± 12.4 µg/L) among yogurt samples. In conclusion, the presence of plant water extracts positively altered yogurt fermentation, enhanced proteolysis of milk protein, and induced EPS production.