Grape Seed Powders as a Source of Phenolic Compounds: UHPLC Orbitrap MS4 Characterization ^†

Abstract

Grape seeds represent a rich source of phenolic compounds that exhibit various health benefits. Therefore, grape seed powders can be a potential functional ingredient in the formulation of different nutritionally valuable food products. The aim of this study was the UHPLC Orbitrap MS4 characterization of phenolic compounds and their derivatives in indigenous (Smederevka, Tamjanika, and Prokupac) and international (Italien Riesling, Muscat Hamburg, Merlot, and Cabernet Sauvignon) grape seed powders. Phenolic compounds were extracted from grape seed powders with 80% methanol containing 0.1% HCl and analyzed by UHPLC Orbitrap MS. The identification of phenolic compounds was conducted based on their monoisotopic mass, MS fragmentation (MS4, MS3, MS2), available standards and literature data. Using standards, gallic, protocatechinic, p-hydroxybenzoic, and vanillic acids were identified in the seed extracts of all analyzed grape varieties. On the other hand, gentisic acid was not detected in the seed extracts of the Smederevka and Merlot varieties. Other phenolic acids and their derivatives, such as ellagic acid (300 m/z), gallic acid hexoside (331 m/z), dihydroxybenzoic acid hexoside (315 m/z), caffeoyl tartaric acid (311 m/z), and coumaroyl tartaric acid (295 m/z), were identified in all analyzed seed extracts based on exact mass and MS2 fragmentation. Commonly present flavan-3-ols (catechin, epicatechin, and catechin gallate) and different B-type procyanidins (B-type procyanidin dimer, trimer, and gallate isomers) were also identified in all analyzed samples. To the best of our knowledge, the procyanidin profiles of the indigenous variety Tamjanika (eight compounds) were analyzed for the first time. Flavonol aglycones (taxifolin and quercetin) and glycosides (quercetin, isorhamnetin, and kaempferol glycosides) were also identified, but their presence in the seeds was selective and closely dependent on grape varieties. In sum, grape seed powders of indigenous and international varieties contain different classes of phenolic compounds, primarily flavan-3-ols, procyanidins, and phenolic acids, which increase and favor their future application in the food industry.