The Effect Of Simulated Digestion In Vitro On The Structural Characteristics And Antioxidant Activity Of Kidney Bean Protein

Kidney bean is one of the main edible legumes for human beings.Kidney bean protein is not only a source of high-quality plant protein,peptide produced by kidney beans have high antioxidant activity,which can improve human immunity,antibacterial and disease resistance.In this study,Skimmed and Peeling Kidney bean protein was prepared with Kidney bean as raw material,and the in vitro digestion model(pepsin digestion for 0~2 h,trypsin digestion for 0~3 h)was used to investigate the antioxidant activity of kidney bean protein in different digestion stages by SDS-PAGE,ultrafiltration technology and Fourier transform infrared spectroscopy.the structural changes of digestive products in different digestive stages were studied,In order to provide a theoretical basis for the development and preparation of high-quality functional and nutritional plant protein food.The results are as follows:1.Antioxidant effect of kidney bean protein and its digestive products was studied: The results showed that the solubility and degree of hydrolysis of kidney bean protein increased during the simulated gastric digestion,the solubility reached the maximum at 120 min and the degree of hydrolysis at 90 min;After simulated intestinal digestion,the protein solubility and degree of hydrolysis increased by 12.05 % and 116.23 %.With the increase of DH and the production of small molecule protein hydrolysates,the antioxidant activity of the products increased significantly after simulated gastrointestinal digestion.Compared with kidney bean protein,the antioxidant activity(total antioxidant capacity,iron reducing capacity,hydroxyl radical scavenging capacity,DPPH radical and ABTS radical)of digestive products increased by296.97%,54.01%,16.82%,10.2% and 43.72%;The antioxidant activities increased by 365.15%,186.10%,49.32%,10.61%and 121.07%during simulated intestinal digestion.2.The antioxidant effect of the simulated digestive products of kidney bean proteins with different molecular weights was studied.The results showed that the digestive products showed strong antioxidative activity after 1.5 h of simulated stomach digestion,especially in the peptides with molecular weight less than 10 kDa;Kidney bean protein was hydrolyzed into small peptides during intestinal digestion,which made the antioxidant activity of different molecular weight digestive products increased to different extent.Especially when the simulated gastrointestinal continuous digestion time was 2 h and 3 h,the molecular weight of kidney bean protein in <10kDa showed the strongest antioxidant capacity.3.The structural properties of kidney bean proteins and their digestive products were studied.It was found that the major storage proteins in kidney beans were mostly hydrolyzed into peptide with molecular weight lower than 14.4 kDa during the simulated gastrointestinal digestion;The secondary structure of kidney bean protein was changed significantly during digestion.The secondary structure of kidney bean protein was mainly composed of ?-sheet(41.14%)and random coil(21.06%),which were confirmed by circular dichroism spectroscopy.During the simulated gastric digestion,the contents of ?-helix and ?-turn increased,while the contents of ?-sheet and random coil decreased with the prolongation of digestion time.During the simulated intestinal digestion,the content of ?-helix decreased firstly and then increased,the content of ?-turn increased,and the contents of ?-sheet and random coil increased firstly and then decreased,and there were significant differences among the indexes;The contents of free and total SH in kidney bean protein decreased greatly after simulated digestion.The contents of exposed SH and total SH were 5.78±0.10 umol/g and 7.05±0.09 umol/g respectively in stomach,and 4.94±0.23 umol/g,6.14±0.20 umol/g,Compared with gastric digestive products,the exposed hydraulics group and total hydraulics group in intestinal digestive products decreased by 17 %and 14.82 %.;In kidney bean protein,the total amount of sulfur-containing amigo acids and essential amino acids were 2.728 ?g/g and 14.903 ?g/g.With the prolongation of digestion time,the total amount of sulfur-containing amino acids in kidney bean protein decreased continuously,and the proportion of essential amino acids increased continuously,and the types and contents of hydrophobic amino acids increased,which indirectly improved the antioxidant activity of digestive products;SEM scanning analysis revealed that kidney bean protein was granular after simulated digestion in the stomach,and arranged randomly to form a fine network structure.With the prolongation of digestion time,the surface of the kidney digested after simulated digestion in the intestine appeared flocculent and formed fine particles.The micro-structure of the protein surface changed significantly.