Iranian grape syrup used as a prebiotic and its effect on the physicochemical, microbiological, and sensory properties of probiotic yogurt

Yogurt is known as a suitable carrier of probiotics. Its supplementation with Iranian grape syrup used as a prebiotic can enhance its sensory and physicochemical properties, as well as improve the viability and growth of probiotics. Therefore, we aimed to investigate the effect of Iranian grape syrup on stirred probiotic yogurt’s rheological, physicochemical, and microbial properties. Probiotic yogurt samples were fortified with 3, 6, and 9% of Iranian grape syrup and evaluated in terms of pH, acidity, syneresis, viscosity, total phenolic and anthocyanin contents, as well as probiotic bacterial counts during 21 days of storage in a refrigerator at 4°C. The results revealed that increasing concentrations of grape syrup inversely affected the yogurt’s pH, so the lowest and highest pH levels were recorded in the samples with the highest syrup concentration and the control (without syrup), respectively. No general trend was observed in acidity despite significant differences in acidity among the syrup-supplemented yogurts and the control (p ≤ 0.05). Syneresis demonstrated an inverse correlation, while viscosity exhibited a direct relationship, with a grape syrup concentration. Monitoring microbial changes in the samples throughout storage revealed a better growth in microbial colonies in the yogurts with higher grape syrup concentrations. According to consumer preferences and physicochemical qualities, the optimal concentration of Iranian grape syrup was found to be 9%. Supplementing yogurt with grape syrup enhances its probiotic viability and metabolic activity. Considering its positive impact on both consumer preferences and product properties, Iranian grape syrup can be utilized as a prebiotic in future research to develop functional and symbiotic yogurts.