Effect of grape (Vitis labrusca L.) pomace dried by different methods on physicochemical, microbiological and bioactive properties of yoghurt

In this study, the effect of grape (Vitis labrusca L.) pomace dried by different methods on the functional properties of yoghurt was examined. Oven- and freeze-dried pomaces were added to the yoghurts at the ratios of 1, 3 and 5%. The freeze-dried pomace had the highest levels of bioactive components, with 34.959 mg GAE/g of total phenolics and 12.586 mg/L DPPH of radical scavenging activity, followed by the pomace oven dried at 80 °C (p < 0.001). At the beginning of the storage period, the yoghurt that contained oven dried, powdered pomace had higher levels of antiradical activity and total phenolics than the yoghurt containing lyophilized pomace (p < 0.05). The total phenolic content, radical scavenging activity, pH, acidity and whey separation decreased, and viscosity increased, during storage for 21 days at 4 °C. Microbiological analysis showed that the amount of lactic acid bacteria did not change significantly (p > 0.05) in yoghurt samples during storage. The sensory analysis done at the end of the storage revealed that the yoghurt samples containing pomace dried in the forced air oven were mostly liked by consumers. This study showed that Isabella grape (V. labrusca L.) pomace can be used as a functional food ingredient in yoghurt production.