Obtenção de um extrato concentrado a partir da casca de uva cv. Alicante Bouschet (Vitis vinifera L.): caracterização química, bioacessibilidade e aplicação como corante

Abstract

The Alicante Bouschet (Vitis vinifera L.) is a grape cultivar with high anthocyanin content in both pulp and skin, which has been used for the production of wines in the Brazilian semi-arid region. This activity generates many residues, still rich in phenolic compounds, mainly anthocyanins. The general objective of the present work was to obtain and characterize a concentrated liquid extract from cv. Alicante Bouschet (Vitis vinifera L.) cultivated in the semi-arid region of Brazil. To this, the most adequate solid-liquid extraction conditions were determined to obtain an extract rich in phenolic compounds with high antioxidant capacity. The concentrated liquid extract was characterized by the phenolic compounds profile by HPLC-DAD, antioxidant capacity by ABTS●+ and ORAC methods, instrumental color by reflectance and antimicrobial activity in vitro using the well diffusion test. The stability of the monomeric anthocyanins and extract color was evaluated during storage at low temperatures. The bioaccessibility of the phenolic compounds was evaluated using an in vitro digestion model. The influence of the extract on the metabolic activity and modulation of the human gut microbiota was studied using an in vitro colonic fermentation model. The extract was added as a dye in a red berries preparation that was added to an ice cream. The stability of the monomeric anthocyanins and of the color was evaluated after the elaboration processes and during the storage of these products. Sensory acceptance of ice creams added with red berries preparation with and without added liquid extract of grape skin was evaluated by using a 9-point hedonic scale. The conditions selected as the most adequate for the extraction were: temperature of 40 °C, 50% v/v ethanol and 2% m/v citric acid. Malvidin-3-O-(6-O-p-coumaroyl)-glucoside and malvidin-3-O-glucoside were the major anthocyanins. The purple-reddish dark and opaque color of the extract remained stable under freezing at -18 ° C for up to 45 days of storage but was less stable under refrigeration at 5 ° C (15 days). The grape skin extract inhibited the growth of all tested bacteria, being more effective against Staphylococcus aureus. The bioaccessibility of monomeric anthocyanins and flavanols was low (23% and 25%, respectively) after in vitro digestion. However, phenolic acids were highly bioaccessible (> 100%) after in vitro digestion and after colonic fermentation, resulting in high antioxidant activity in these phases. Although 24 h of in vitro colonic fermentation were not enough to stimulate the microbiota growth, the production of short chain fatty acids (SCFAs) in fermented extract indicate that the extract favored the metabolic activity of the intestinal microbiota. Therefore, the extract could have a potential prebiotic effect for the long-term modulation of the microbiota. The grape skin concentrated liquid extract could be used as a natural dye in red berries preparations and ice cream.