Comparison of Drying Methods and Their Effect on the Stability of Grasevina Grape Pomace Biologically Active Compounds

Valorisation of grape pomace, a by-product of the winery industry, has been pushed into the spotlight in recent years since it can enable lower environmental impact, but it can also bring an added value to the wine production process by recovering several grape pomace biologically active compounds. The first step that allows for grape pomace reuse is its drying, which should be carefully performed in order to preserve the biologically active compounds' stability. In this study, the effects of different drying methods on the stability of polyphenols, tannins and tartaric acid in grape pomace (Vitis vinifera) cv. Grasevina were investigated. In particular, vacuum drying (at different temperatures: 35, 50 and 70 degrees C), conventional drying at 70 degrees C and open sun drying were performed and the drying kinetics was described using Peleg's model. Considering the processing time and thermodynamics, vacuum drying at 70 degrees C was the most convenient processing method. Polyphenols were highly stable during drying, and slight degradation occurred during vacuum drying at 35 and 50 degrees C. Tannins and tartaric acid were more prone to degradation depending on the drying method applied and showed the greatest stability during vacuum drying at 70 degrees C.