Voltammetric Behavior, Flavanol and Anthocyanin Contents, and Antioxidant Capacity of Grape Skins and Seeds during Ripening (Vitis vinifera var. Merlot, Tannat, and Syrah).

Nawel Benbouguerra,François Garcia,Tristan Richard,Cédric Saucier

doi:10.3390/antiox9090800

Abstract

Skin and seed grape extracts of three red varieties (Merlot, Tannat, and Syrah) at different stages of ripening were studied for their total phenolic content (TPC) by using the Folin-Ciocalteu assay and for their total antioxidant capacity (TAC) by using spectrophotometric and electrochemical assays. Flavanol and anthocyanin compositions were also investigated using Ultra Performance Liquid Chromatography coupled with Mass Spectrometry (UPLC-MS). Results showed that seeds had the highest phenolic content and the highest antioxidant potential compared to skins at all stages of ripening. The highest TPC and TAC values were measured in seeds at close to veraison and veraison ripening stages. In skins, the highest values were found at the green stage, it was in accordance with the flavanols content. The voltammetric measurements were carried out using disposable single walled carbon nanotubes modified screen-printed carbon electrodes (SWCNT-SPCE). Three peaks on voltammograms were obtained at different oxidation potentials. The first anodic peak that oxidized at a low potential describes the oxidation of ortho-dihydroxy phenols and gallate groups, the second peak corresponds to the malvidin anthocyanins oxidation and the second oxidation of flavonoids. The third voltammetric peak could be due to phenolic acids such as p-coumaric acid and ferulic acid or the second oxidation of malvidin anthocyanins. The high linear correlation was observed between antioxidant tests and flavanols in skins (0.86 ≤ r ≤ 0.94), while in seeds, ‘r’ was higher between electrochemical parameters and flavanols (0.64 ≤ r ≤ 0.8).

Highlights

Vitis vinifera is the most economically important species of grape vine in the world with 78 million tons of grapes production in 2018
Content,antioxidant antioxidantcapacity, capacity, flavanol, anthocyanin contents of grape seed extracts of three red grape varieties were studied at different stages of ripening
At all stages of and seed extracts of three red grape varieties were studied at different stages of ripening

Summary

Introduction

Vitis vinifera is the most economically important species of grape vine in the world with 78 million tons of grapes production in 2018 (see http://www.oiv.int/en/oiv-life/oiv-2019-report-on-the-worldvitivinicultural-situation). Grapes consumed as fresh fruits, juices, and other processed products, contain many phenolic compounds which are mostly located in seeds and skins [1]. These compounds are synthesized in response to various biotic and abiotic stress such as fungal invasion, UV irradiations, ozone, and heavy metal ions [2]. Their content changes depending on the grape variety, soil, climatic conditions, and the ripening stages [3]. The flavonoids (C6-C3-C6) are located in both skins and seeds and the anthocyanins

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