Polyphenolic Profile and Antioxidant Activity of Green Extracts from Grape Pomace Skins and Seeds of Italian Cultivars

Abstract

The possibility of industrial exploitation of winemaking products, as for all byproducts of vegetal origin, constantly deals with a raw material (grape pomace, GP) whose chemical composition and functional properties vary over time depending on the varietal and geographical origin of the grapes, the climatic conditions (vintage effect), and the winemaking technique. This work studied the compositional variability of polyphenolic skin and seed extracts from GP derived from white and red winemaking of different Italian grape varieties. The total polyphenolic content (GAE), the main classes of polyphenolic compounds, and the DPPH index were determined. Seed extracts were always richer in total polyphenols and condensed tannins and had higher antiradical activity (DPPH) than skin extracts: 144–298 mg GAE/g d.w. extract for skins and 327–540 mg GAE/g for seeds; the DPPH values were 1.77–3.40 mg AAE/g for skins and 3.10–10.48 mg AAE/g for seeds. Furthermore, it was verified that the evaluation of the GAE index of seed extracts, offering a good estimate of the antiradical properties (DPPH index), could represent a simple and rapid method for selecting the best lots of seeds to be used. Conversely, GP skins could be used as flour in the food industry due to their high content of dietary fiber and the presence of flavonols, which possess very interesting functional properties. Important differences in the flavonols profile were observed both between cultivars and between unfermented and fermented pomace.

Optimization and Validation of Procyanidins Extraction and Phytochemical Profiling of Seven Herbal Matrices of Nutraceutical Interest

“…In this study, the experimental screening design focused on the impact of five extraction factors, which include the polarity of the solvent, solid/solvent ratio, acid content, ultrasound treatment, and agitation lengths. To assess procyanidins extraction, grape pomace was selected as a well-known source of a vast type of procyanidins [48]. As the solvent composition is of importance in the extraction of procyanidins, which is a flavonoid subclass, different hydromethanolic combinations were applied.…”

From Field to Waste Valorization: A Preliminary Study Exploring the Impact of the Wine Supply Chain on the Phenolic Profile of Three Sardinian Pomace Extracts

“…The metabolomics of grape pomace are clearly affected by the various steps of the production chain, influencing the quality and quantity of nutrients, particularly polyphenols, contained within. Consequently, these factors determine the final properties of the derived extracts and their potential applications [10,11].…”

“…At the end of the ripening and collection, grapes of Malvasia, Vermentino and Nasco were treated following the white vinification, which involved a short and low impacting crushing followed by the pressing and separation of pomace and must [11]. The concentration of alcohol, sugar content, organic acid, malic acid, lactic acid, total polyphenols, and pH of the resulting musts, obtained after the separation from pomace, were measured (Table 3).…”

“…The measured parameters were influenced by the vinification process and the sampling period. According to Guaita et al, the musts were sampled immediately after the pressing step and before alcoholic fermentation took place (unfermented) [11]. As expected, the alcohol concentration of musts was low, ranging from 0 ± 0.1 to 0.09 ± 0.01 (%v/v), while the sugar concentration was high, ranging from 238.5 ± 9.0 to 257.3 ± 16.0 g/L (Table 3).…”

“…They are usually in conjugated forms with sugar residues through β-glycosidic linkages (O-glycosylated) [28]. Normally, the presence of quercetin as aglycone in pomace is due to the enzymatic hydrolysis of the 3-O-glycosides forms during the winemaking process [11]. The low concentration of quercetin aglycone found in the white pomace can be explained by the absence of the fermentation step of the pomace during the white winemaking.…”