Grape stem extracts: Polyphenolic content and assessment of their in vitro antioxidant properties

Abstract

Grape stems constitute a scarcely investigated class of vinification byproducts with limited reports on their bioactive polyphenol content and/or industrial applications. Herein we present the outcome of our investigation on various grape stems extracts from native Greek grape varieties, concerning the assessment of their total polyphenolic content (TPC), the quantification of the individual bioactive polyphenols and the detailed evaluation of their antioxidant properties. Results obtained indicate that grape stems are particularly rich in flavonoids and stilbenes, with trans-resveratrol and ɛ-viniferin present in considerably high concentrations. They also exhibit significant antioxidant properties, which were determined by DPPH• radical scavenging and FRAP assays (modified to fit into a high throughput approach). Additional experiments concerning the inhibition of CuSO4-induced LDL oxidation and the reduction of intracellular reactive oxygen species (ROS) indicated that most extracts tested display an extreme capability to prevent the oxidation of LDL−lipoprotein at very low concentrations and to reduce the intracellular ROS levels, exhibiting IC75 values between 10.4 μg and 49.1 μg per gram of extract. Results herein reveal that grape stems represent a rich source of high added value natural antioxidants, particularly stilbenes such as trans-resveratrol, which may be used by pharmaceutical, food and cosmetic industries.