Study On The Interaction Between Carrot Dietary Fibers And Bound Polyphenols Based On Microbial Fermentation

Dietary fiber and polyphenols are usually studied separately because of differences in their chemical structures,physicochemical and biological properties.With the continuous research of dietary fiber,some studies have shown that a number of polyphenols,namely bound polyphenols,exist in dietary fiber.However,the present studies mainly focused on carbohydrate components in dietary fiber,but not enough attention was paid to the polyphenol components in dietary fiber.Carrots,as a widespread consumed vegetable,are a good source of natural antioxidants,and previous studies had confirmed that carrots have plenty of dietary fiber and bound polyphenols.However,many by-products of carrot are not fully utilized and usually discarded which causing serious pollution to the environment.Therefore,the aim of this study was to optimized the removal of polyphenols from carrot dietary fiber,and investigate the effect of bound polyphenols on the antioxidant and prebiotics properties of carrot dietary fiber as well as elucidate the effect of bound polyphenols on the fermentation and antioxidant properties of carrot dietary fiber(CDF)in vivo and in vitro.The main research results are as follows:(1)The polyphenols were removed from CDF by alkaline extraction to obtain dephenolized dietary fiber(CDF-DF).The optimized conditions of extracting polyphenols from CDF were solid-liquid ratio of 1:8.5,the treat temperature of ?-amylase 66?,the addition of protease of 0.2%and the treat temperature of amyloglucosidase 60?,respectively.FT-IR spectroscopy illustrated that the major functional group of CDF-DF and CDF shared most of the key features,despite changes in the amplitude of some functional groups.Scanning electron microscopy(SEM)and X-ray diffraction were further performed demonstrating no significant structure differences between CDF-DF and CDF.Moreover,antioxidant properties,including superoxide anion radical,hydroxyl radical and DPPH radical scavenging activity of CDF-DF were significantly lower than that of CDF.In addition,CDF was more conducive for the growth of Lactobacillus rhamnosus as compared with the CDF-DF.In summary,the above results concluded that there was no significant change of the dietary fiber after removal of bound polyphenols,and the bound polyphenols contributed significantly to the antioxidant and prebiotics properties of dietary fiber from carrot.(2)In vivo:as compared with CDF treatment,16S rRNA pyrosequencing of the in vitro human fecal fermentation samples showed that dephenol ized carrot dietary fiber(CDF-DF)treatment decreased operational taxonomic units(OTUs),ACE and Chaol indexes,increased Firmicute/Bacteroidetes(F/B)ratio and relative abundance(RA)of Parabacteroides at phylum,restrained RAs of typical beneficial bacteria,as well as improved RAs of various harmful bacteria at genus.Meanwhile,short-chain fatty acids(SCFAs)contents were lower while pH value was higher in CDF-DF group than these in CDF group.Furthermore,the CDF-DF-fed mice exhibited higher MDA content and lower SOD and GSH-Px activities in colon.These results revealed that bound polyphenols significantly contribute to the fermentation and antioxidant properties of CDF in vivo.(3)In vitro:The fermentation properties including flora data,SCFAs content and pH value of CDF and CDF-DF groups in vitro are similar to the results in vivo.In addition,the combination of bound polyphenols and CDF-DF(CDDP)could recover these indexes influenced by the removal of bound polyphenols in vitro fermentation samples.Cellular antioxidant activity(CAA)value of CDF-DF was lower than that of CDF and CDDP.The indexes of fermentation characteristics and CAA value verified the bound polyphenols in the dietary fiber significantly promoted the fermentation properties and antioxidant properties of CDF.This study shows that bound polyphenols as a part of dietary fiber has a significant effect on the fermentation and antioxidant properties of dietary fiber.These results have important theoretical significance and practical value for the development of high value-added products of carrot dietary fiber,and can also provide scientific guidance and experimental basis for diet nutrition.