Bioactive compounds recovery by freeze concentration process from winemaking by-product

Grape pomace is the main solid residue of wine industry, containing high amounts of phenolic compounds. Considering its high potential, an extraction procedure was optimized for maximal recovery of anthocyanins from grape pomace (Vitis vinifera L.) using citric acid as a generally recognized as safe (GRAS) acidulant in water. Volume of solvent (3.2-36.8 mL), time (14.4-165.6 min) and pH of solvent (1.12-4.48) were the studied variables. Furthermore, the best condition to obtain extract rich in anthocyanins was submitted to the gravitational block freeze concentration process. The performance of the process was evaluated and cryoconcentrated and ice fractions were analyzed for physicochemical properties, bioactive compounds content, and antioxidant activity. Interaction, linear, and quadratic effects for volume and pH of solvent were significant by analysis of variance (ANOVA). The experimental design allowed the prediction for maximal recovery of anthocyanins (10 mL of solvent at pH 1.8). The bioactive composition of the optimized grape pomace extract was influenced by the cryoconcentration process. After three cycles using gravitational block freeze concentration, the total phenolics and monomeric anthocyanins were approximately 4 and 5 times higher than the initial condition of the extract, respectively. Consequently, an increase in antioxidant activity was observed. The increase in the concentration of bioactive compounds reached a process efficiency of 93% (stage 1) for phenolic compounds and 91% (stage 2) for anthocyanins. Therefore, the final water-based optimized method is safe and has a low cost and the concentrated extract certainly showed higher concentrations of total phenolics and anthocyanins, compared to the initial extract. The proposed clean extraction method and cryoconcentration technique can be considered important strategies for recovering and valuing grape pomace components, improving the approach to the circular economy concept in the wine industry.

Changes in phytochemical composition of Merlot grape and wine induced by the direct application of boron

In this study the effect of the direct application of different concentrations of boron in grape bunches on the phytochemical composition of grapes and wine was evaluated. The experiment was carried out by direct application to the grape bunch of different concentrations (0, 1.0, 2.0, 4.0 and 8.0 g/L) of boron solution, in two consecutive vintages, 2018 and 2019. The wines were elaborated by the same microvinification method. Histological analyzes by optical microscopy and phenolic profile by HPLC-DAD were performed on the grapes. The wines were analyzed by HPLC-DAD and ICP-MS for phenolic profile and elemental composition, respectively. Histological analyzes of the grape skin showed an increase in the presence of polyphenols in the cellular tissue of grapes treated with different concentrations of boron when compared to the control samples in both vintages. The addition of boron influenced the phenolic profile of the grapes, resulting in an increase in the content of anthocyanins and flavanols. Regarding to wines, the treatment of grapes by direct application of boron significantly influenced the chemical composition of wines. In 2018, the application of 2 g/L of boron showed a significant increase in the concentration of malvidin and delphinidin in wines. The application of 1 g/L showed the highest concentration of malvidin, delphinidin and peonidin in the 2019 vintage. The boron content increased in the wine samples according to the boron concentrations applied to the grape. Thus, it is possible to produce chemically distinct wines with the direct application of boron to the grapes.