Effect Of Different Processes On Phenolic Compounds And Antioxidant Activity Of Quinoa(Chenopodium Quinoa Willd)

Whole grains are considered as a healthy food for prevention of chronic diseases,including obesity,cardiovascular disease,diabetes,and cancer,as suggested by epidemiological studies.The beneficial effects of whole grains have been demonstrated to be associated with the significant amount of phenolics compounds and their antioxidant activity.Quinoa(Chenopodium quinoa Willd)represents one of the most popular foods of Andean origin due to its complete nutritional and functional values.It is not only a great source of protein and vitamins,but also an excellent source of phenolic compounds.Thus,it has been receiving widely attention of scientists in the field of functional food.Recently,much attention has been paid to investigate nutritional compounds of quinoa,and the study on phenolic compounds of quinoa is far from being valued as phenolics of fruits and vegetables.There are several studies fouced on phenolic compounds of quinoa,but the variety and the growing area was relatively simple.It is difficult to indicate the general information of its phenolic compounds.Therefore,it is necessary to comprehensively investigate the difference in phenolic compounds and their biological activities among different quinoa varieties.In addition,the changes in phenolic compounds of quinoa,especially the bound phenolics,during different processes are unknown.Therefore,7 colored quinoa varieties with different origins were analyzed to determine the total saponin conten,the free and bound phenolics compounds as well as their antioxidant activity and the inhibitory activity of phenolics against ?-glucosidase.Meanwhile,the changes in phenolic compounds and their antioxidant activity during different processes were preliminarily investigated in order to provide a theoretical basis for the processing and utilization of quinoa resources.(1)Characterization of saponins and phenolic compounds:antioxidant activity and inhibitory effects on ?-glucosidase in different colored quinoa varietiesThis study aimed to investigate the content of saponins and phenolic compounds in relation to their antioxidant activity and ?-glucosidase inhibition activity of 7 colored quinoa varieties from different origins.The results showed that the total saponin content was significantly different among 7 varieties and ranged from 7.51 to 12.12 mg OAE/g DW.Darker quinoa had a higher content of phenolic compounds and antioxidant activity than that of light varieties.Nine individual phenolic compounds were detected in free and bound form using HPLC,with gallic acid and ferulic acid representing the major compounds.The Pearson's coefficients analysis showed that free and bound phenolics(gallic acid and ferulic acid in particular)exhibited high linear correlation with their corresponding antioxidant values,indicating that these specific phenolic compounds could be used as important indicators of antioxidant activity in colored quinoa.In addition,the free phenolic extracts of quinoa exhibited higher inhibitory activity against ?-glucosidase than the bound phenolic extracts.Particularly,the IC50 values of free phenolic extracts from Q-w1,Q-r1 and Q-w2 were much lower than acarbose,suggesting that these varieties have a potential function in the control of postprandial hyperglycemia.These findings imply that colored quinoa with abundant bioactive phytochemicals could be an important natural source for preparing functional food ingredients.(2)Effect of DOM on total saponins,phenolics compounds and antioxidant activity of quinoaQuinoa was milled in order to investigate the effect of DOM on the total saponins,free and bound phenolics,and their antioxidant activity as evaluated by oxygen radical absorbance capacity(ORAC)and ferric reducing antioxidant power(FRAP)assays.Results showed that saponin can be effectively removed from quinoa during milling process,and improved itssensory quality.As the DOM increased from 0 to 27.23%,the content of total saponin,phenolic,flavonoid and the total ORAC and FRAP value of quinoa decreased by 41.8%,31.5,41.4,39.6 and 40.7%,respectively.However,the contribution of bound fraction to total phenolic and the antioxidant activity changed very little.In addition,the content of nine phenolic compounds decreased significantly with increasing DOM.Therefore,low DOM(<15.89%)is recommended for acceptable sensory quality and retention of phytochemicals during quinoa milling process.(3)Effect of germination on macronutrient,phenolic compounds and antioxidant activity of quinoaQuinoa was germinated in order to investigate the effect of germination on macronutrient,phenolic compounds and antioxidant activity of quinoa.Results showed that germination for 48 h could significantly increase the content of total and soluble protein of quinoa,and reduce the starch content.Meanwhile,in vitro starch digestibility of quinoa was improved after germination.Germination could significantly increase phenolic content and their antioxidant activity.After germination for 48 h,the content of total saponin,phenolic and flavonoid as well as the total ORAC and FRAP value increased by 16.46%,42.0%,33.7%,31.6% and 26.8%,respectively.Furthermore,the percentage contribution of bound fraction to total content increased significantly during germination.Eight individual phenolic compounds were detected in free or bound form using HPLC,and the content increased with the prolongation of germination time,with the exception of gallic acid.In summary,germinated quinoa seeds have more antioxidative phenolics,and provide important information for the processing and utilization of quinoa as functional food ingredient.(4)Effect of simulated in vitro digestion on phenolic compounds and antioxidant activity of quinoaThis study aimed to investigate the effect of simulated in vitro digestion on the content of total phenolic and flavonoid,phenolic compounds and their antioxidant activity of quinoa.Results showed that the content of phenolic compounds and their antioxidant activity in quinoa were highest after oral,gastric and intestinal digested fractions.The major release step of phenolic compounds and their antioxidant activity was gastric fraction.After oral,gastric and intestinal digestion and colonic fermentation,the bioaccessibility of phenolic and flavonoid in quinoa was 40.99% and 20.15%,respectively.Therefore,the results could provide important information for the evaluation of nutritional efficacy of phenolic compounds in quinoa.