In this study, five varieties of hybrid grapes were processed into juice to assess the influence of variety, destemming process and enzyme addition on juice quality, including yield, physicochemical properties and bioactive compounds. The results highlighted that while the processing methods had some impact on juice quality, the inherent grape variety remained the most significant factor. Although similar treatments were applied to all varieties, there were differences in the quality attributes of the juice. In general, red grape juice had a higher polyphenol content and antioxidant capacity than white grape juice. Four phenolic acids, eleven flavonols, five flavan-3-ols and five anthocyanins were identified. While the polyphenolic profile of each sample depended on the treatment and the variety, regardless of the variety, destemming was found to increase the yield by around 10-15%, while the addition of enzyme improved the yield by around 20-30%. Although the addition of enzymes led to a higher polyphenol content, it changed the color profile of the juice as a result of the pigment's skin extraction. In contrast, the destemming process did not influence the color of the juice, but at the same time, it reduced the health benefits due to the removal of potential bioactive compounds from the stems.
Keywords: antioxidant capacity; bioactive compounds; destemming; enzyme addition; grape juice; hybrid grape; polyphenols.