Bioactive non-coloured polyphenols content of grapes, wines and vinification by-products: Evaluation of the antioxidant activities of their extracts

Abstract

Abstract The comparative quantization of main non-coloured polyphenols, the assessment of total polyphenolic content (TPC) and the detailed evaluation of the antioxidant activities of various grape-based products – from the harvest stage up to the production of the corresponding wines – are presented. The material studied consisted of grape tissues (berries, seeds and skins) of native Greek Vitis vinifera cultivars, which provided polyphenol-rich extracts via an optimized ultrasound extraction procedure, while the respective wine samples were condensed by a novel extraction procedure using XAD-4 adsorption resin column. The extraction methods accuracies were thoroughly validated and the polyphenolic content of extracts was assessed by HPLC–DAD and photometric methods. Their antioxidant properties were evaluated by following assays, modified to fit into a high throughput approach: DPPH radical scavenging, FRAP, inhibition of CuSO4-induced LDL oxidation and the reduction of intracellular reactive oxygen species (ROS) in smooth muscle cell cultures. Seed samples exhibited the highest TPC values, which are well correlated with their significant antioxidant properties in all assays performed. Of special interest is the significant capability of the tested extracts to prevent the LDL oxidation at very low concentrations. Furthermore, the good correlation between the antioxidant activities assessed for the LDL oxidation inhibition and the intracellular ROS assays is indicative of the possible in vivo antioxidant properties of the extracts. Results herein reveal the considerable antioxidant potential of the Greek grapevine production and exploits their vinification by-products as a potential inexpensive source of high added value antioxidants.