Chemical Composition, Antioxidant Activity And Bioavailability Of Four Legume Vegetable Polyphenols

Polyphenols are the most critical non-nutritional factor in plant foods,such as fruits,vegetables and cereals.They have the function of anti-oxidation,anti-inflammatory and anti-tumor effects.Snap bean(Phaseolus vulgaris L)and cowpea(Vigna unguiculata)are popular leguminous vegetables in China.Leguminous vegetables are not only rich in basic nutrients,but also contain high polyphenol content.As far as we know,little has been reported on the polyphenols,antioxidant activity and bioaccessibility of leguminous vegetables.In this study,four kinds of leguminous vegetables(purple cowpea,cowpea,king pole bean and white pole bean)were selected to evaluate their nutritional components.Moreover,the phenolic content,the flavonoid content,antioxidant activity and chemical components of free and bound extracts in four kinds of leguminous vegetables were systematically compared.Furthermore,the bioaccessibility and antioxidant activity of free and bound polyphenols in purple cowpea with higher phenolic content were studied based on the INFOGEST model.The main results are as follows:1.The basic nutrients in four kinds of leguminous vegetables.The national standard method was used to determine the content of basic components.The results indicated that leguminous vegetables are rich nutrients.Among them,the moisture of leguminous vegetables ranged from 91.02 to 92.24%.Analyzed by dry matter of leguminous vegetables,the main nutrient in legumes was crude protein(24.94?28.21%),followed by total sugar(12.86?19.68%)and crude fiber(11.33?14.59%).The content of fat,ash and reducing sugar were relatively lower.Then,based on 7 basic nutrients(crude protein,crude fat,ash,carbohydrate,crude fiber,total sugar and reducing sugar),the results of principal component analysis showed that the nutritional value order of the four kinds of leguminous vegetables was king pole bean,purple cowpea,cowpea and white pole bean.2.The phenolic compositions and antioxidant activities in four kinds of leguminous vegetables.The results showed that the phenolic and flavonoid content in free and bound extracts of four kinds of leguminous vegetables were positively correlated with their antioxidant activities.The free and bound extracts in purple cowpea had the highest phenolic content,flavonoid and antioxidant activities.The phenolic and flavonoid content in bound extracts by acid and alkaline hydrolysis is significantly higher than that of enzymatic hydrolysis.Moreover,the free phenolic content is about 2?4 times higher than that of the bound polyphenol by acid and alkaline hydrolysis,and the free flavonoid is about 1?4 times higher than that of the bound flavonoid by acid and alkaline hydrolysis.The main phenolic acids in the free extracts are protocatechuic acid,gallic acid and sinapic acid,and the main flavonoids are epigallocatechin,epicatechin,catechin and rutin.The main components in the bound extracts are protocatechuic acid,p-coumaric acid and gallic acid.3.Study on the stability of polyphenols in the gastrointestinal tract and bioaccessibility of purple cowpea.The powder,free polyphenols and bound polyphenols of purple cowpea with higher phenolic content were studied based on the INFOGEST model.The results displayed that gastric stage was more favorable for the stability of phenolic compounds during in vitro digestion.After in vitro digestion,the order of phenolic content and flavonoids was powder,free polyphenols and bound polyphenols,the trend of dialyzable rate is in line with the trend of phenolic content and flavonoids.The main phenolic compounds from different fractions were also different.The main released phenolic substances in powder are genistin,rutin,epicatechin and sinapic acid during in vitro digestion;the main phenolic substances in free polyphenols are daidzein,p-coumaric acid,p-hydroxybenzoic acid and genistein;the released phenolic compounds in bound polyphenols are very low,gallic acid,sinapic acid and genistein were released in the oral-gastric stage,while p-hydroxybenzoic acid was the only released substance in the small intestine-OUT stage.