Stability of Individual Phenolic Compounds and Antioxidant Activity During Storage of a Syrah Grape Seed Extract

The valorization of winery by-products is a sustainable strategy for receiving valuable bioactive compounds. The aim of this study was to obtain Syrah grape seed extract and investigate the stability of extract phenolic compounds and antioxidant capacity. Separated grape seeds from grape pomace were dried under two different conditions: 23 °C for 10 days and 40 °C for 24 h. Polyphenols were extracted from the dried seeds using 70% aqueous ethanol under magnetic stirring at 600 rpm for 3 h. The yield, color, nutrition value, and mineral contents of the extract were determined. The obtained extracts from the seeds dried at different temperatures were concentrated using a vacuum evaporator. The concentrate was subsequently divided into three forms: liquid, lyophilized, and dried at 40 °C. The individual phenolic components of the lyophilized grape seed extract were determined by HPLC. All extracts were stored at 4 °C and 23 °C for 10 months. The effect of the grape seed drying conditions, extract forms, storage temperature, and time on the total phenolic content, total flavonoids, procyanidins, and antioxidant capacity of the extracts was investigated. Changes in these parameters were evaluated at 0, 3, 6, and 10 months of storage. Degradation kinetics on the basis of antioxidant activity during extracts storage were calculated. Additionally, the individual phenolic composition of liquid and lyophilized Syrah grape seed extracts stored for 10 months was determined by HPLC. The degradation degree of the individual compounds in the extracts was calculated.