| In order to comprehensively develop and utilize agricultural by-products in the food industry and broaden the source of dietary fiber(DF),this article used microwave technology to treat the DF in agricultural by-products from different sources(sweet potato pomace,apple pomace,soybean pomace,defatted rice bran).The aim was to increase the mass fraction of soluble dietary fiber(SDF),improve the physicochemical properties of DF,and evaluated the effect of microwave modification on the probiotics properties by investigating the in vitro fermentation characteristics of dietary fiber different from sources before and after microwave in different intestinal types.Among them,rice bran has a wide range of sources and is rich in nutrients,but it is difficult to be used by gut microbiota,consequently microwave combined enzymatic modification was used to modify the DF of rice bran for comparing the effects of single and combined modification on its probiotic properties.The main findings were as follows:(1)The DF in sweet potato pomace,apple pomace,soybean pomace,and defatted rice bran was treated by microwave to obtain eight groups of DF samples before(WRBF,WAF,WSF,WRBF)and after(MWRBF,MWAF,MWSF,MRBBF)modification.The mass fraction of SDF was improved to different degrees after microwave modification,which increased by 63.11%,4.51%,358.79% and 106.78%respectively,among them the soybean DF increased the most.Scanning electron microscopy(SEM)observed that the overall trend of changes was the appearance of holes on the DF surface,which increased the accessibility edges of DF,and the apparent structural damage to MWAF was the most obvious.Through X-ray diffraction(XRD)analysis,the results shown that the microwave modification had none obvious effect on the crystal structure of DF.Moreover,it could be seen from the thermal stability curve that the final mass residue after microwave was increased,and the thermal stability of MWSF had been significantly improved.The increased in SDF mass fraction and accessibility edges enabled DF after microwave combine with water,oil,cholesterol,nitrite ion and other substances better,significantly increased the dissolution of phenolics,and enhanced the antioxidant capacity.The comparison found that the improvement of SDF mass fraction was not related to the comprehensive improvement of functional properties,which meant the improvement of the functional properties on DF after microwave modification was the combined effect of the increase in SDF and the exposure to the edge of accessibility.(2)The fecal microbiota of three healthy donors(FD1: Prevotella enterotype;FD2 and FD3: Bacteroides enterotype)were selected for in vitro fermentation of eight kinds of DF.For the three different types of microflora,FD1 had a stronger ability to degrade DF than other fecal fermentation systems,FD2 was relatively weak,and FD3 had a more diverse and richer flora composition.Among the four types of DF,the rice bran DF was fermented slowly during the 0-48 h compared to the other three groups of DF,which was related to its higher antioxidant properties and insoluble fiber composition,and the impact of microwave on the fermentation characteristics was weak.In addition,microwave treatment degraded a large number of insoluble components in MWSF into oligosaccharides,which promoted the growth of beneficial bacteria such as Bifidobacterium in all three groups of fecal fermentation systems.At the same time,the MWSF group had better fermentation characteristics,the yield of short-chain fatty acids(SCFAs)significantly increased compared with WSF group,which made the p H lower.(3)Microwave combined enzymatic was used to further modified the rice bran DF to obtain ME-WRBF.The research shown that although the mass fraction of SDF in ME-WRBF had decreased after multiple treatment,while the swelling power of MEWRBF was significantly improved,which shown a looser and porous structure compared with MWRBF.Therefore,it might conducive for the attachment of gut microbiota on ME-WRBF.With the help of in vitro fermentation model,it was found that the ME-WRBF group reduced the gas production and p H value during the fermentation process,and showed a significant increase in the content of each SCFA and the total amount at 24 h.The Shannon diversity index of the ME-WRBF group increased significantly,and the ME-WRBF had a significantly different microbiota structure from the WRBF group.Furthermore,the ratio of Firmicutes and Bacteroidetes in ME-WRBF group was reduced,which might adjust the gut microbiota to a beneficial structure. |
