STUDY OF THE TOTAL PHENOLIC CONTENT OF QUINOA SEED EXTRACTS USING GREEN SOLVENTS FROM AN EXPERIMENTAL DESIGN

The quinoa (Chenopodium quinoa Willd.) is a seed considered as a functional food due to the presence of several compounds associated with health benefits, among them, polyphenols. In view of this, Bolivian (BoWQ, BoRQ, respectively) and Brazilian (BrWQ) white and red quinoa seeds were evaluated for total phenolic content (TPC). Therefore, an experimental design was designed containing 11 experiments, eight axial and three central points, to evaluate the effects of the independent variables, temperature (32-68 °C), time (6.5-19.5 h) and concentration of ethanol (19-76%) over the TPC extraction. TPC analyzes were performed in triplicate, using the Folin-Ciocalteau method, using a UV-vis spectrophotometer (Shimadzu, model UV-2550) at 760 nm and using a gallic acid curve as a standard (0.001-0.020 mg/mL in ethanol) and the results expressed in milligrams of gallic acid equivalent per g of dry extract (mg EAG/g). Response surfaces and a first-order polynomial for each variety were applied to predict the response variable. The adequacy of the models was predicted considering the pure error, regression analysis (R2) and ANOVA using the Statistic 7.0 program and the Tukey test applied to identify the differences in the means (p<0.05). As for TPC, the BrWQ variety ranged from 20.36 to 35.12 mg GAE/g extract, time had no significant influence on the extraction of phenolic compounds. Knowing that higher values of the coefficients of the polynomial equation express a stronger effect on a specific parameter and the positive sign indicates a direct relationship between the dependent and independent variables analyzed, the concentration of ethanol had a stronger effect (β3=+3.08) when compared to temperature (β1= 3.08). Their best responses were found at the extreme points of the planning, being 35.12 mg EAG and 34.91 mg EAG in extractions at 68 °C; 19.5 hrs; 76% ethanol and 32°C; 6.5 hrs; 19% ethanol, respectively. In BoWQ, temperature had the most significant effect (β1=-3.42) in relation to time, while the ethanol: water ratio was not significant. Thus, the experiment with the smallest design variables (32 °C; 6.5 h; 19% ethanol) had the highest TPC (32.17 mg EAG). In BoRQ, the ethanol concentration showed the strongest effect (β3=+6.28), and the highest response (42.84 mg EAG) was identified in the experiment with extraction at 68 °C; 6.5 hrs; 76% ethanol. The statistical model demonstrated the efficiency of green solvents in the extraction of phenolic compounds, as well as the influence of the parameters analyzed in this process. In the same way that the answers of the central points showed reproducibility of the experiment. Knowing that phenolics are phytochemicals, known to have high antioxidant activity, and their consumption is associated with several health claims, quinoa shows up as a food rich in these compounds and that can be explored in the elaboration of extracts for use in the food industry, foods, nutraceuticals or cosmetics. However, the antioxidant activity and the identification of these compounds present in the extracts can be further elucidated in future studies.