In vitro Antioxidant and Antibacterial Activities of Quinoa Flavonoids Extracted by Ethanol-Ammonium Sulfate Aqueous Two-Phase System

Quinoa (Chenopodium quinoa Willd.) is a functional and ideal food for human nutrition and an Andean seed-producing crop. In this study, ultrasonic-assisted extraction of total flavonoids in Quinoa with ethanol (C2H5OH)-ammonium sulfate ((NH4)2SO4) aqueous two-phase system was performed based on the Box-Behnken experimental design principle. The highest extraction rate of TFQ under the condition of 28% C2H5OH -14% (NH4)2SO4 aqueous two-phase extraction system was used to analyze the variance of TFQ extraction rate as the response value. The multiple quadratic linear regression equation was obtained by a three-factor three-level response surface method. The extraction rate= 74.28+1.78 A+0.10 B+0.38 C+0.20 AB+0.05 AC+0.05 BC+1.000E-002 A2-0.94 B2-0.69 C2. The response surface analysis showed that the best extraction conditions of aqueous two-phase were the crude TFQ mass fraction 20.6%, pH 7.18, NaCl mass fraction 2.23% and the maximum value predicted by the extraction rate model was 75.929 3% (P=0.994). The average extraction rate of TFQ was 75.3%, according to the optimal two-aqueous phase extraction conditions. The ETFQ has varying degree of scavenging effect on hydroxyl radical, oxygen free radicals, nitrite and ·ABTS+ compared with vitamin C. Among them, the scavenging effect of the ETFQ on hydroxyl radical, oxygen free radicals and ·ABTS+ was greater than vitamin C, except nitrite. Also, the ETFQ has the strongest inhibitory effect on E. coli and Bacillus subtilis, and the inhibitory rate can reach up to high dose 97.59 and 98.44%, MIC is 1.56 mg/mL; the second is the inhibition of S. aureus, MIC is 6.25 mg/mL. It has the weakest inhibitory effect on Salmonella. The antibacterial rate was positively correlated with the ETFQ mass concentration. The results help to discover the medicinal effects of quinoa in addition to nutrition to carry out more in-depth research and increase economic value. © 2021 Friends Science Publishers