Abstract
Yogurt production with starter culture at 41 degrees 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. (similar to 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 mu g/mL; respectively) compared to plain-yogurt (26.3 +/- 0.4 mu g/mL). The presence of G. mangostana and L. barbarum resulted in an increase (p < 0.05) of total solids content (similar to 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 mu g/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.