Effects Of Different Processing Methods On Phenolic Substances And Antioxidant Activities Of Beans

Phenolics are secondary metabolites with strong antioxidant properties.Beans which are good sources of phenolic substances have recently become a research hotspot in the field of food nutrition.In order to determine the variations of phenolic substances of legumes under different processing methods,the effects of soaking,boiling,grinding and germination on total phenolics,total flavonoids,total anthocyanin content,condensed tannin content,total antioxidant capacity,DPPH free radical scavenging ability and hydroxyl free scavenging ability of black soybeans,small black kidney beans,mung beans,adzuki beans,red kidney beans,purple speckled kidney beans were studied.The flavonoids were detected by ultra performance liquid chromatography-tandem quadrupole mass spectrometry(UPLC-MS/MS).Multivariate analysis was carried out on the detected datas.The difference components of beans before and after processing were screened out,and the advantages and disadvantages of processing methods of beans were further explored.The results of research are as follows.1.The content of phenolic substances in most beans decreased significantly or did not change significantly during the soaking process.The increase of total phenolic content in soaked mung beans,total flavonoid content in soaked small black kidney beans,total anthocyanin content in soaked red kidney beans were found(p<0.05).There may be some compounds with antioxidants but non-phenolic substances in beans,such as proteins,polysaccharides,etc.Soaking caused the dissolution of these substances,resulting in no significant correlation between some phenolic indicators and antioxidant capacities(p> 0.05).2.Boiling caused significant decreases or indistinctive changes in the total phenolic content,total anthocyanin content,condensed tannin content,DPPH free radical scavenging activities and hydroxyl free scavenging activities of most beans but significant increases in total flavonoid content and total antioxidant activities of black soybeans and black adzuki beans(p<0.05).All indicators of black soybeans and black adzuki beans increased significantly during and grinding(p<0.05).Therefore,black soybeans and black adzuki beans can be a good source of processing for beans and pulping can preserve phenolic substances preferably.3.Germination did not cause significant changes or indistinctive changes in content of phenols and antioxidant activities of adzuki beans and purple speckled kidney beans(p>0.05).Germination caused significant increases in the content of phenols and antioxidant activities of black soybeans,small black kidney beans,mung beans and red kidney beans and maximum value of content of phenols and antioxidant activities existed in germination 4 or 5 days.The total phenolic content of mung beans germinated for 5 days reached 4.61 times of that in unprocessed beans.Therefore,mung beans are the most suitable beans for germination.The antioxidant activities had significant positive correlation with the total phenolic content and the total flavonoid content(p<0.01).In addition,Germination caused significant decreases in total anthocyanin content(p<0.05)and total anthocyanin content did not exhibit significant correlation with other indicators(p>0.05).4.Based on the UPLC-MS/MS detection platform,197 kinds of flavonoids were detected in black soybeans and small black kidney beans before and after boiling and grinding.The results of principal component analysis,hierarchical cluster analysis and orthogonal partial least squares discriminant analysis showed that boiling and grinding caused significant effects on flavonoids in black soybeans and small black kidney beans.Through the screening of differential flavonoid compounds,it was found that boiling and grinding caused a large amount changes in flavonoids.And there were significant difference between boiled and grinded beans.In this paper,the effects of soaking,boiling,grinding and germination on phenolic substances and antioxidant capacities of six beans were studied.The differences in the changes of phenolic substances of beans during processing were analyzed,and the processing methods for the good retention of phenolic substances of beans were determined.The results provide a basis for the variations of phenolic substances during processing.