Antioxidant Capacity and Phenolic Profile of Defatted Seed Powder Derived from Organically Grown Vine Crops

Grape seeds derived from winemaking pomace represent a significant waste stream with potential for valorization due to their rich phenolic content. The present study aimed to assess the phenolic composition and antioxidant potency of defatted grape seeds powder (DP) resulting after oil extraction through three different methods (i.e., cold stirring (ST), ultrasound-assisted extraction (US), and microwave-assisted extraction (MW)) from two grape varieties (i.e., Fetească Regală and Merlot) grown under organic farming conditions. The phenolic profile was determined using High-performance liquid chromatography with diode array detection and mass spectrometry operating in electrospray ionization positive mode, while the total phenolic content was determined using an adapted Folin-Ciocalteu technique, The samples' antioxidant properties were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging ability assessments, as well as Cupric ion reducing antioxidant capacity and Ferric reducing antioxidant power assays. The phenolic qualitative profile differed between the two varieties and was unaffected by the defatting method. Instead, at the level of each variety, significant variations (p<0.05) were observed in the quantity of phenolic compounds, depending on the defatting method. Moreover, the total phenolic content was significantly higher in the MW-DP compared to ST-DP and US-DP (p<0.05), particularly from Fetească Regală grape seeds. The DPPH assay demonstrated the highest antioxidant activity in MW-DP from Fetească Regală. The study underscores the importance of the extraction methods and grape variety on the phenolic profile and antioxidant potency of DP. These findings suggest potential applications in pharmaceuticals, functional foods, and cosmetics, offering sustainable solutions for grape pomace utilization.