Comparison,Digestibility And Stability Of Polyphenols From Different Parts Of Walnut

In this thesis,walnut was used as raw material to compare the polyphenol differences of Diaphragma juglandis fructus,walnut pellicle,and flowers of Juglans regia prepared by methanol condensation reflux extraction,ultrasonic extraction and enzymatic extraction.The effects of gastric and intestinal digestion on walnut polyphenols in vitro were studied.In addition,the effects of different storage conditions and exogenous additives on the stability of walnut polyphenols were compared.The results of this paper can provide a theoretical basis for the application of walnut polyphenols in functional food.Firstly,the differences of polyphenols in different parts of walnut prepared by three methods were compared.The phenolic compounds of Diaphragma juglandis fructus,walnut pellicle,and flowers of Juglans regia were extracted by methanol condensation reflux extraction,ultrasonic extraction and enzymatic extraction.The structure,content and antioxidant capacity of phenolic compounds obtained by different extraction methods were compared.The results showed that 50 kinds of phenols were identified by HPLCMS/MS,including 41 kinds of phenols in Diaphragma juglandis fructus,32 kinds in walnut pellicle and 29 kinds in flowers of Juglans regia.The content of tannin in walnut pellicle was higher than that in Diaphragma juglandis Fructus and flowers of Juglans regia.PLSR correlation analysis was used to analyze the aggregation of 50 phenols.The results showed that more than 70% of the structural changes of phenols were caused by the differences between different parts of walnut,which had low correlation with extraction methods.The phenolic compounds in walnut all have significant antioxidant activities,among which the antioxidant capacity of walnut pellicle is the highest.Secondly,the changes of walnut polyphenols after digestion in vitro were investigated.The results showed that the digestive enzyme promoted the hydrolysis of tannin and the release of combined polyphenols,increased the content of polyphenols in the extract and increased the antioxidant capacity.After digestion by intestinal fluid,under the action of bile,enzyme and p H,the phenol content decreased obviously,and the antioxidant capacity decreased accordingly,that is,walnut polyphenols were mainly digested in the gut.After digestion,the recovery of phenolic acid was high,about 85.22%-119.60%.The recovery of tannin was the lowest,except for flowers of Juglans regia,the recovery rate of walnut pellicle and tannin was not more than 10%?Finally,the effects of p H,temperature and additives on the stability of walnut polyphenols were determined.Walnut polyphenols obtained by ultrasonic assisted extraction method were selected as the research object to study the stability of polyphenols under different storage conditions such as p H,temperature and sunshine intensity.The results showed that walnut polyphenols had good thermal stability,and were more suitable for dark storage in neutral environment with p H 3-7 and lower temperature.Through the determination of metal ions,carbohydrates,oxidants,antioxidants,stabilizers and preservatives,it is concluded that the use of oxidants,stabilizers and metal ions such as iron and copper will affect the stability of polyphenols,while the use of other antioxidants and preservatives in the use standards of food additives will not affect the stability of polyphenols.