Green Preparation And In Vitro Digestion Characteristics Of Soluble Dietary Fiber From Coffee Peel

Coffee peel(CP)is a good source of dietary fiber(DF)and polyphenols.However,due to the limitations of production technology and other conditions,it is often discarded as industrial waste,which not only causes a waste of resources,but also causes serious pollution to the environment.Therefore,further research to better utilize it is of great practical significance.In this study,the SDF from coffee peel rich in conjugated polyphenols was extracted by UAE-DESs method through response surface optimization.The effects of in vitro digestion on the structure and biological activity of CPSDF were investigated.This study provides a theoretical basis for revealing the functional activity of dietary fiber of coffee peel and lays a theoretical foundation for the development of high value-added products of dietary fiber of coffee peel.Specific findings are as follows:(1)For SDF prepared from coffee peel,the DES with the highest yield rate was selected by single factor experiment,namely choline chloride/urea with molar ratio of 1:2.According to the response surface experiment,the SDF yield was used as the index,and the four factors of DES water content,liquid-solid ratio,ultrasonic power and ultrasonic time were selected to determine the optimal preparation conditions according to the regression model optimization:Under the conditions of choline chloride/urea water content of 39.91%,liquid-solid ratio of 32.37 mL·g-1,ultrasound power of 305.20 W,and ultrasound time of 33.80 min,the SDF yield of coffee peel was the highest(10.74±0.14%),which was close to its predicted value of 10.80%.(2)Taking CPSDF as the research object,the changes in structure and biological activity of CPSDF during in vitro digestion were investigated by simulating oral,gastric,and small intestinal digestion.The results showed that the structure of CPSDF became loose and porous during digestion,but it still retained the polysaccharide skeleton.The average particle size was the largest in the gastric digestion stage,and double peaks were observed in the small intestine stage.Phenolic substances were released and covalently bound to SDF.The free radical scavenging ability of DPPH,ABTS and FRAP decreased after in vitro digestion(P<0.05).The inhibitory activity of gastrointestinal digestion of α-glucosidase was increased,and the inhibitory activity was higher than that of acarbose(P<0.05).(3)UPLC-MS/MS metabolomics technology was used to study the distribution changes of combined polyphenols and metabolites of CPSDF during in vitro digestion.A total of 550 metabolites were detected before and after in vitro digestion,among which flavonoids and phenolic acids were the two largest groups of differential metabolites during digestion,accounting for 82.18%of the total metabolites.OPLS-DA and metabolic pathway analysis showed significant differences in bound phenolic profiles before and after in vitro digestion.This indicates that phenolic compounds are significantly affected by in vitro gastrointestinal digestion.In addition,the changes in antioxidant and enzyme inhibitory activities were consistent with the trend of total phenolic content.