Study On Antioxidant Activity And Stability Of Three Quinoa Polyphenols

This article used three kinds of quinoa grown in Tibet as raw materials,and their polyphenol compounds were systematically studied.The optimization of the extraction process conditions were explored,the crude extract of quinoa polyphenols was separated and purified,the components with high antioxidant activity were identified,and the stability of the components and the effect of antioxidant activity on oil were determined.These studies provide a basis for the effective utilization of quinoa polyphenols and a reference for the comprehensive use of quinoa.(1)The effects of five factors on the extraction amount of three kinds of quinoa polyphenols were investigated with Ultrasound-assisted.The results showed that the order of the influence of the five single factors on the extraction amount was:extraction temperature>material liquid ratio>extraction time>extraction power>ethanol volume fraction.The best optimum conditions for the extraction of three kinds of quinoa polyphenols were as follows:material liquid ratio was 1:24 g/m L,extraction time was 42 min,extraction temperature was 42?,extraction power was 205 W,and ethanol volume fraction was 70%.Under these conditions,the extraction amounts of three quinoa polyphenols were(2.65±0.02)mg/g,(2.44±0.02)mg/g,and(2.36±0.03)mg/g,respectively.The three models of quinoa polyphenol extraction reached extremely significant levels(p<0.01),The lack of fit item was not significant,and the coefficient of determination R² was 0.9483(white),0.9707(red),0.9620(black),respectively,and the model fitted well with the experimental values.(2)The polyphenols of quinoa were enriched with macroporous resin D-101 and eluted with different concentrations of ethanol,and the components with high antioxidant activity were selected.The ethanol fractions with high phenolic contents and antioxidant activities were treated with gradient elution on C18 SPE column,then seperated and identified by LC-MS/MS.The results showed that the content of polyphenol in the 50%ethanol fraction was the highest.There were mainly 8 bioactive substances in this component,including protocatechuic aldehyde,ferulic acid,luteolin,quercetin,rutinum,luteolin4'-O-glucoside,delphinidin3-galactoside,and quercetin 3-O-glucuronide,among which quercetin was the most abundant substance.(3)The effects of temperature,p H,metal ions,preservatives(Potassium sorbate)and oxidants(H₂O₂)on the stability of three quinoa polyphenols were studied.The results showed that at low temperature and p H?4,it was beneficial to the stability of the three quinoa polyphenols,and under high temperature and alkaline conditions,the stability of polyphenols declined.The ions of Ca²⁺,Mg²⁺,Zn²⁺and Al³⁺had little effect on the stability,while the ions of Fe³⁺and Cu²⁺were not conducive to the stability of polyphenols.A low concentration of potassium sorbate solution was beneficial to the stability of polyphenols;when the concentration was too high,the stability of polyphenols would decrease.The oxidant H₂O₂ had a greater impact on the stability,and had a certain destructive effect on the structure of the polyphenols.(4)The antioxidant effects of three quinoa polyphenols on lard and soybean oil were studied.The results showed that:The three quinoa polyphenols all had a certain antioxidant effect on lard and soybean oil.The three quinoa polyphenols had the effect of inhibiting the oxidative rancidity of oils.Without added antioxidants,soybean oil was more susceptible to be oxidized than lard.