CITRIC ACID WATER-BASED SOLUTION FOR GRAPE POMACE ANTHOCYANINS RECOVERY

Anthocyanin isolation from agri-byproducts is attracting attention for the full utilization of these compounds. Red wines are good sources of anthocyanins and the grape pomace by-product of red wine also contains a considerable amount of anthocyanins. In this research, a bio-safer and eco-friendlier, anthocyanin extraction method was studied. The extraction procedure was optimized for recovery of anthocyanins from Montepulciano grape pomace (Vitis vinífera) using citric acid as a generally recognized as safe (GRAS) acidulant in water. Extraction conditions were optimized following a central composite design based on a 33 factorial design with 4 repetitions of the central point, resulting in 18 experiments, performed in random order. The independent variables were volume of water: citric acid solution (1:10; 1:20 and 1:30, w/v), extraction time (45; 90 and 135, min) and pH (1.8; 2.8 and 3.8). Total monomeric anthocyanins were the dependent variable used in the optimization. The statistical significance of the factors was evaluated by ANOVA. The adequation and fit quality were assessed by p-lack of fit and determination coefficient (R2). The experimental and predicted values of response were compared in confidence intervals at 99% level. Anthocyanins measurements were performed by pH differential method and results were expressed as mg of maldivine-3-glycoside equivalent per 100g of fresh sample. The experimental results showed that the content of anthocyanins varied from 4.12 to 15.48 mg 100g−1. The dataset results were fit by response surface methodology coupled with multiple regression to describe the effect of process variables on recovery of anthocyanins.The resulting models were significant (p < 0.001) and did not show a lack of fit (p >0.01), indicating that the model, describes the effects of the dependent variable with good predictability. The coefficient of determination was 0.86, and adjusted R2 >0.71. According to the proposed models, linear and quadratic effect of the volume of water: citric acid solution, and pH significantly affected the dependent variable evaluated. The variable extraction time did not present significant effect. For volume and pH, the linear effect was negative, however, the quadratic effect contributed positively to response. Considering that quadratic effect of the variable was positive, it is stated that the model presents a minimum extraction rate for the evaluated response. Based on this, the prediction of the optimal combination of volume of water: citric acid solution, pH and time for extraction of anthocyanins from grape pomace was 40 mL of solvent, pH value of 2.8, and 31 minutes. Then, to obtain extracts with higher concentrations of anthocyanins according to the proposed model, lower volumes and low pH values are desirable, and moderate extraction times are preferentially chosen for practical applications. Anthocyanins have been widely used in industries due to their natural coloring, antioxidant and therapeutic properties, therefore presenting an environmentally friendly method of extracting anthocyanins is relevant. To improve recovery of anthocyanins, it is suggested to combine these extraction techniques with emerging methods of concentration of bioactive compounds, such as block freeze cryoconcentration. Therefore, resulted models can be used to predict response values for all variables evaluated.