Effect Of Pretreatment On Structure And Properties Of Solubie Dietary Fiber From Buckwheat Bran

Buckwheat bran is a by-product of the primary processing of buckwheat,has a variety of health benefits,and is a natural source of active ingredients such as dietary fiber.However,because of its coarse taste,it is difficult to be accepted by the general consumer and is often used as fertilizer or animal feed.In this study,buckwheat bran was pretreated with extrusion,steam explosion,microwave,roasting,superheated steam,ultrasonic,and enzymatic hydrolysis to improve its comprehensive utilization.The effect of different treatments on the extraction rate of buckwheat bran soluble dietary fiber(SDF)was investigated.The composition of SDF monosaccharides and bound phenols were determined by gas chromatography(GC-MS)and high-performance liquid chromatography(HPLC).The effect of pretreatment on the structure of SDF was explored by scanning electron microscopy(SEM),thermogravimetry,Fourier infrared spectroscopy,and X-ray diffraction(XRD).The changes in the hydration characteristics,antioxidant properties,in vitro hypoglycaemic capacity,bacterial inhibition,and other functional properties of SDF before and after treatment were comprehensively evaluated.It can provide theoretical guidance and a scientific basis for the application of buckwheat bran SDF in food industry.Results were obtained as follows:(1)The pretreatment damaged buckwheat bran biomass structure to different degrees.The buckwheat bran SDF extraction rates were improved most effectively by extrusion and were increased by 121.47% compared with the control group.Buckwheat bran SDF comprised six monosaccharides,namely rhamnose,arabinose,xylose,mannose,glucose,and galactose.The total monosaccharides of SDF from buckwheat bran with extrusion,steam explosion treatment was over 2-fold of that of the control group.Pretreatment altered the composition of bound phenols in buckwheat bran SDF,of which the total amount increased significantly after extrusion treatment,6.4-fold of that of the control group.Besides,four additional monomeric phenols were detected compared to the control group,namely p-hydroxybenzoic acid,paeoniflorin,erucic acid,and rutin.(2)Pretreatment changed the compact microstructure of buckwheat bran SDF to varying degrees of looseness.By different pretreatments,the thermal stability of SDF was improved,the color of SDF was changed,the rheological properties of SDF were stable,and the SDF solution showed shear-thinning non-Newtonian behavior;buckwheat bran SDF had typical polysaccharide absorption peaks,and were natural cellulose type I crystalline structure,but their relative crystallinity were decreased.(3)The hydration properties(water retention,water-holding,oil absorption,swelling),antioxidant properties(ABTS,DPPH,FRAP),in vitro hypoglycemic capacity(α-amylase inhibition rate,glucose adsorption capacity),bile acid and nitrite ion adsorption capacity,and bacterial inhibition capacity of buckwheat bran SDF were significantly enhanced by pretreatments.In addition,the bile acid adsorption capacity of SDF from buckwheat bran steam explosion treatment is the best,followed by that of extrusion treatment.This study improved the physical and nutritional properties of SDF of buckwheat bran through pretreatment.It could promote the further processing and utilization of buckwheat by-products,and provide the scientific basis for the development of new functional buckwheat food.