Polyphenolic Characterization of Grape Skins and Seeds of Four Italian Red Cultivars at Harvest and after Fermentative Maceration

Abstract

Agro-industry byproducts can still contain large amounts of phenolic compounds, and one of the richest sources are grape skins and seeds as grape pomace, both fermented (red winemaking) and unfermented (white winemaking). The residual polyphenolic content depends on various factors such as grape variety, vintage, and winemaking technique. In this work, four red grape varieties cultivated in northern Italy were studied: Albarossa, Barbera, Nebbiolo, and Uvalino. The work was aimed at studying the polyphenolic composition of skins and seeds from fresh grapes and from the corresponding pomace after fermentative maceration, to assess the actual importance of the varietal differences when processing winemaking byproducts for the extraction of phenolic compounds. The skin and seed extracts were prepared by solvent extraction with a 50% hydroalcoholic solution. The polyphenolic composition of all extracts was determined by spectrophotometry and high-performance liquid chromatography (HPLC); the content and the monomer composition of condensed tannins were determined by phloroglucinolysis; the antioxidant capacity was measured with the ABTS (2,2’-azinobis-(3-ethylbenzothiazoline-6- sulfonate)) method. The antioxidant capacity was higher for the seeds than for the skins, and it was positively correlated with the condensed tannins content. Significant differences in polyphenolic composition of fresh grape skins and seeds were observed between the different cultivars. In particular, Barbera and Albarossa skins were significantly distinguished from Nebbiolo and Uvalino skins for a higher content of anthocyanins and a lower content of vanillin-reactive flavans and condensed tannins; regarding seeds, Barbera and Albarossa had a lower content of vanillin-reactive flavans, proanthocyanidins, and condensed tannins than Nebbiolo and Uvalino. The winemaking process extracted the phenolic compounds to a different extent from skins and seeds, regardless of the cultivar. The differences between cultivars in the polyphenolic profile disappeared after fermentative maceration.

Potential of grape byproducts as functional ingredients in baked goods and pasta

“…Among different grape peels cultivars, Barbera and Albarossa presented higher anthocyanins and lower vanillin-reactive flavans and condensed tannins amounts compared to Nebbiolo and Uvalino varieties, whereas grape seeds from Barbera and Albarossa varieties had smaller quantities of vanillin-reactive flavans, proanthocyanidins, and condensed tannins compared to Nebbiolo and Uvalino, these differences disappearing after fermentative processes application (Guaita & Bosso, 2019).…”

“…In others, the increase of the absorbance occurs during the reaction of the antioxidant with the chromogenic reagent, for example, ferric reducing antioxidant power and cupric reducing antioxidant capacity (Shahidi & Zhong, 2015). Guaita and Bosso (2019) reported higher antioxidant activity of grape seeds compared to peels, underlining a positive correlation with the tannins content. Tkacz et al (2019) revealed that grape seeds have higher antioxidant activity ranging from 207.9 to 479.7 µmol trolox equivalents (TE)/g compared to peels for which it varied from 17.6 to 339.2 µmol TE/g in function of the variety, with higher values for the red ones (Table 3).…”

Proanthocyanidins Ameliorated Deficits of Lipid Metabolism in Type 2 Diabetes Mellitus Via Inhibiting Adipogenesis and Improving Mitochondrial Function

“…Total contents of proanthocyanidins were determined with vanillin assay [60][61][62]. Standard curve and calibration curve were obtained by measuring absorption of different concentration of standards solution.…”

Stearoyl-CoA Desaturase-1 Enzyme Inhibition by Grape Skin Extracts Affects Membrane Fluidity in Human Colon Cancer Cell Lines

“…In this context, numerous studies have been conducted in colon cancer cells to investigate the effects of grape extracts on the modulation of cell membrane components and on the viability and metastatic potential [23][24][25]. Grape skin and grape seed extracts are made up of different polyphenolic compounds that elicit multiple beneficial biological activities [26]. The resveratrol is able to accumulate sphingolipids in cell membranes, leading to cell cycle arrest and apoptosis [27].…”