Effect of UV-Vis Irradiation on Enzymatic Activities and Physicochemical Properties of Four Grape Musts from Different Varieties

The influence of ultraviolet-visible irradiation on some quality attributes (pH, soluble solids content, color parameters, absorption spectrum, vitamin C, total acidity, total phenolics, formol index, and total and reducing sugars) and polyphenol oxidase, peroxidase, and pectinmethylesterase activities of fresh grape juices was investigated. Grape juice was made from two varieties of white grapes (Victoria and Dauphine) and two varieties of pink grapes (Emperor and Red Globe). Each juice was irradiated for 140 min with a high-pressure mercury lamp of 400 W that emits in a range between 250 and 740 nm. Polyphenol oxidase was not completely inactivated during irradiation, reducing only 80% of its initial activity in juices from white grapes and only 50% in those from pink grapes. On the contrary, peroxidase was completely inactivated. A slight or nonexistent variation was observed in most of the measured physicochemical parameters, showing high stability during irradiation. Only vitamin C and color had a significant variation, with an average decrease of 30% for vitamin C in all varieties and a more important variation of color parameters in the pink varieties than in the white ones.