Screening grape seeds recovered from winemaking byproducts as sources of reducing agents and mammalian a-glucosidase and a-amylase inhibitors

Grape seeds collected from vinification of various grape varieties were extracted by supercritical CO2 for oil recovery. The defatted residues thus obtained were considered as a re-utilisable co-product and assessed for phenolic content, reducing capacity and inhibitory activities against mammalian alpha-amylase and alpha-glucosidase enzymes. Supercritical CO2 treatment led to higher recovery of anthocyanins. Reducing capacity of phenolic extracts reached up to ~2200 mmolFe(II)/ kg, much higher than that of various natural phenolic sources. The anthocyanin-rich extracts showed the highest inhibitory effectiveness towards alpha-glucosidase (I50 value equal to ~40 microg gallic acid equivalents (GAE)/mL ~ half than acarbose). Inhibitory effectiveness towards alpha-amylase activity was similar among grape varieties, with I50 values comparable to that of acarbose and correlated with proanthocyanidin contents. These results could pave the way for an efficient processing of grapes, including cascade processes, namely: winemaking, oil extraction from recovered grape seeds and phenolic extraction from defatted grape seeds as potential cost-effective nutraceuticals.