Impact of dehydration on retention of bioactive profile and biological activities of different grape (Vitis vinifera L.) pomace varieties

The effects of drying method [sun (7 days), oven (72 h at 60 °C) and freeze (∼72 h)] and grape (Vitis vinifera L. cv. Pinotage, Shiraz and Sauvignon Blanc) variety on pomace fatty acid composition, polyphenolic content and antioxidant capacity were evaluated. Furthermore, the influence of sun-dried pomaces on rumen microbial diversity was assessed in vitro. Freeze-dried Shiraz had the highest proportions of 18:1n-9, 18:2n-6, total monounsaturated fatty acid (MUFA), polyunsaturated fatty acids (PUFA) and content of polyphenolics compared to other drying × variety interactions (P ≤ 0.05). Freeze-dried Sauvignon Blanc had the highest proanthocyanidin content and antioxidant activity for both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) relative to other drying × variety interactions (P ≤ 0.05). Regardless of variety and inclusion level, grape pomace variety reduced bacterial species abundance, but improved species diversity, evenness and richness compared to the control (P ≤ 0.05). Overall, freeze-dried Shiraz had the best fatty acid profile and highest polyphenolic content, while freeze-dried Sauvignon Blanc had the highest proanthocyanidin content and antioxidant activity.