Utilization of pomegranate and black grape seed by-products in yogurt production: Effects on phenolic compounds and antioxidant activity

The present study investigated the potential utilization of pomegranate and black grape seed by-products of the food industry in yogurt production. Specifically, we examined the effect of polyphenols on antioxidants in yogurts produced using two different starter cultures: classical yogurt culture (Lactobacillus delbrueckii subsp. bulgaricus + Streptococcus thermophilus) and yogurt culture supplemented with L. casei. Various parameters, including pH, acidity, viscosity, fat content, protein content, dry matter content, color, microbiological properties, and sensory attributes, were analyzed in the yogurt products. The present findings indicate that incorporating pomegranate and grape seed powder and using different starter cultures significantly affected the yogurt's phenolic content and antioxidant activity. Furthermore, we observed decreased phenolic content and antioxidant activity during the 21-day storage period. Interestingly, yogurts produced with pomegranate seed powder and L. casei culture exhibited higher antioxidant activity than the other samples. Importantly, none of the yogurts containing pomegranate and grape seed powders had microbial counts below 107 cfu/g for L. delbrueckii subsp. bulgaricus, S. thermophilus, and L. casei, indicating no adverse effects on probiotic properties. Sensory evaluation revealed that the yogurt product prepared with grape seed powder and a combination of yogurt culture (L. delbrueckii subsp. bulgaricus + Streptococcus thermophilus) and L. casei was particularly well-received. In conclusion, the functional properties of grape seed powder and pomegranate seed powder make them suitable natural ingredients for enhancing the antioxidant activity of yogurt. The study highlights the potential of utilizing these by-products to develop yogurt products with added health benefits.