LC-MS/MS profiles, antioxidant potentials and enzyme inhibition effects of local grape seed extracts: Correlation between antioxidant capacity and enzyme inhibition potency

The wine, molasses, and juice industries produce large amounts of grape seed (GS) waste. Depending on the variety, GS have different concentrations of phenolic compounds which are important in preventing oxidative stress (OS). OS plays an important role in numerous disorders such as cancer and neurodegenerative diseases. Redox-regulatory enzymes, thioredoxin reductase (TrxR) and glutathione S transferase (GST) play a role in intracellular defense mechanisms against OS and inhibition of them is targeted in anticancer strategies. The antioxidant characteristics of possible bioactive sources, like GS, have not been thoroughly studied. In addition, studies on the content profile and bioavailability potential of local varieties are quite limited. So, in this study the antioxidant properties of methanol and water extracts of GS from the grape varieties grown in Iğdır, Türkiye, were investigated. Their phenolic contents were determined by LC-MS/MS. In the following studies, inhibitory potencies of the extracts on TrxR and GST were analyzed. The most abundant phenolic was found as catechin in both extract types. The highest total phenolic content (TPC) (6000 ± 174 mg/100 g GAE) was found in the methanol extract of Erzincan Karası seed, while the highest total flavonoid content (TFC) (738 ± 142 mg/100 g CE) was found in the water extract of El-Hakkı seeds. Antioxidant properties were found to be either higher or at similar levels compared to standard antioxidants. The extracts were found to effectively inhibit enzymes. Besides, relationships between TPC and TFC levels of extracts and their antioxidant activities and enzyme inhibition potentials were evaluated statistically by correlation analysis.