Interaction Effects On A Gold Nanoparticles-based Assay For Antioxidant Capacity Evaluation Of Polyphenols

Polyphenol is a kind of common antioxidant in food.Accurate evaluation of the total antioxidant activity of polyphenol in fruits and vegetables is a great significance for evaluating their nutritional value and potential physiological effects.Some methods have been applied to the determination of the total antioxidant activity of polyphenols,but no uniform or recognized standard method used for that.The gold nanoparticles(AuNPs)assay has been used for determining the total antioxidant activity of polyphenols in various foods,but the accuracy and reliability of the assay have not been systematically evaluated.Variety of polyphenolic has been found in food and the inclusion of complex matrices such as proteins.The interaction between polyphenolic and the effect of complex matrices show influence on the total antioxidants of polyphenols in samples.Therefore,the purpose of this paper is to validate the reliability for evaluating the antioxidant activity of the AuNPs assay.The effects of the interaction of polyphenols and matrix effect on the results of AuNPs were systematically investigated,and the results were systematically compared with those of the commonly used antioxidant methods such as ABTS,DPPH and FRAP,so as to comprehensively evaluate the accuracy and reliability of the method.The main findings are as follows:(1)By analyzing the correlation coefficient between the antioxidant activity of the polyphenol monomer and its AuNPs morphology and optical properties,it was verified that the AuNPs method could determine the antioxidant capacity of the monomer polyphenol.12 representative polyphenolic compounds were selected,including 5 types of hydroxybenzoic acid,hydroxycinnamic acid,flavonoids,flavonols,flavanols,the antioxidant activity and the optical properties and morphological characteristics of AuNPs were characterized.It was found that the antioxidant capacity of polyphenols was negatively correlated with the particle size of the nanoparticles,and positively correlated with the absorption value at 540 nm.Meanwhile,the stronger the antioxidant capacity,the darker the colloid solution and the blue shift of LSPR characteristic absorption peak.However,there was no significant correlation between the results of the AuNPs method and the other methods(ABTS,DPPH,and FRAP).(2)The effect of polyphenol interaction on the results of AuNPs assay to evaluate total antioxidant capacity was investigated.Preparing 12 groups of equimolar mixtures,including 7 groups of binary polyphenols and 5 groups of ternary polyphenols.The total antioxidant capacity of each group evaluation by AuNPs assay had no significant correlation with the three commonly methods.By analyzing the estimation variation between the observational and the theoretical antioxidant capacity,the results of AuNPs were higher than other assays.The maximum estimation variation for the antioxidant ability of binary polyphenol mixtures was +167.33%,and the maximum estimation variation for the determination of ternary polyphenol compounds reached +254.32%.The antioxidant capacity was seriously overestimated when evaluated the antioxidant capacity by AuNPs assay.(3)The effect of matrix effect of the sample on the results of AuNPs assay to evaluate total antioxidant capacity was investigated.First,the antioxidant activity of the extracts of raspberry,grape,orange,apple,bell pepper and tomato were evaluated by different assay.The total antioxidant capacity determined by AuNPs assay was significantly correlated with others and effected by the total phenol content and the total flavonoid content.However,the matrix effect of each extract had a greater impact on the determination of gallic acid and rutin recovery by AuNPs method than other assays.The results showed that the antioxidant capacity of polyphenols was correlated with the morphology and optical properties of AuNPs.However,compared with other assays such as DPPH method,ABTS method and FRAP method,the performance of AuNPs assay was more significantly affected by the interaction of polyphenols and the matrix effect of samples.Therefore,as a method for the evaluation of antioxidant capacity of food,AuNPs method needs more in-depth and systematic research.