Study On Modified Preparation Of Rice Bran Dietary Fiber And Its Properties

Rice bran,as one of the most important by-product in rice processing,is rich in diatery fiber,amino acids,unsaturated fat acids and biofunctional materials.Studies have shown that rice bran gives health benefits including control of obesity,diabetes,gastrointestinal disorders and cardiovascular diseases.Nowadays,people are paying more attention and interesting on rice bran.Moreover,it is so popular to researchers for the research of diatery fiber.It reveals that dietary fiber has better physicochemical and functional properties because of main components.It becomes the focus research in recent years.However,the research on rice bran dietary fiber is still at the starting stage in China.Rice bran has a low rate of dietary fiber extraction.It exists a lot of issues such as the low extraction rate,chemical agents introducing,inconvenient for mass production and other issues.In this study,the fresh diatery fiber was used to prepare the solubal diatery fiber and insolubal diatery.Three different methods of extrusion technology,liquid hot water pretreatment,high hydrostastic pressure treatment were used to improve the production of rice bran diatery fiber.The mechanisms of different methods were explored at the same time.Simultaneously,the physicochemical properties,functional properties and antioxidant activity of rice bran dietary fiber were further studied.The main results were shown as follows:(1)In this paper,the process of different pretreatment assisted enzymatic hydrolysis to extract rice bran soluble dietary fiber and insoluble dietary fiber was optimized by single factor and orthogonal experiments with fresh rice bran.The results showed that rice bran soluble dietary fiber had high productivity of 30.35%under the condition of extrusion temperature of 130 ?,the screw speed of 200 r/min,material moisture content of 20%,a-enzyme dosage of 2.0%,enzymatic hydrolysis temperature of 75 ?,hydrolysis time of 90 min,pH of 6.0.According to the single factor and orthogonal experiments,rice bran insoluble dietary fiber had high productivity of 56.21%under the condition of extrusion temperature of 130 ?,the screw speed of 200 r/min,material moisture content of 20%,extraction temperature of 50 ?,extraction time of 60min,feed liquid ratio of 1:55,alkali concentration of 0.25mol/L.(2)The process of high hydrostatic pressure treatment and liquid hot water pretreatment assisted enzymatic hydrolysis to extract rice bran dietary fiber was optimized by single factor experiments,with fresh rice bran as the material.The results showed that rice bran dietary fiber had high productivity under the condition of high hydrostatic pressure treatment time of 15 min,treatment pressure of 400 MPa,high hydrostatic pressure treatment feed liquid ratio of 1:15,liquid hot water pretreatment temperature of 200 ?,treatment time of 20 min.The effect of different pretreatment assisted enzymatic hydrolysis to extract rice bran dietary fiber conditions was researched.At the same time,the physicochemical properties of rice bran dietary fiber,such as retention ability,water binding ability,swelling ability and bounding fat ability,were analyzed by SEM(scanning electron microscope),FTIR(fourier transform infrared spectroscopy)and DSC(differential scanning calorimeter).The results of physical and chemical properties showed that surface morphology of rice bran dietary fiber was loose and honeycomb.Inter body was composed of cellulose material,which makes the thermodynamics of soluble dietary fiber is relatively stable.Meanwhile,rice bran dietary fiber pretreated by the method of extrusion,high hydrostatic pressure treatment and liquid hot water pretreatment assisted enzyme hydrolysis had higher retention ability,water binding ability,swelling ability,bounding fat ability.Dietary fiber can be seen from rice bran under fourier transform infrared spectroscopy.Rice bran dietary fiber had a typical characteristic absorption peak of saccharides.The structure characterization and physiological functional properties were improved,compared with the un-pretreatment processing.The characteristic absorption peaks and positions of rice bran dietary fiber did not change significantly compared with the one under non-pretreated rice bran dietary fiber.However,the pretreatment of hydrogen bonds between molecular chains of dietary fibers was interrupted.It also makes polyphenol structure exposed as well as many carboxyl groups.(3)The pretreated rice bran dietary fiber can adsorb an amount of glucose.Meanwhile,its adsorption capacity is significantly higher than that of rice bran,which can effectively reduce the concentration of glucose in the small intestine to a lower level.The glucose dialysis delay index can predict that dietary fiber reduces postprandial blood glucose as an important in vitro indicator of delayed absorption of glucose in the gastrointestinal tract.In addition,the value of delayed index value of glucose assisted dialysis of the soluble dietary fiber extracted by extrusion was larger than high hydrostatic pressure treatment.The value of the delayed dialysis index of the glucose obtained by the pretreatment was higher than that without pretreatment.Liquid hot water pretreatment had no significant effect on increasing the value of glucose dialysate delay index of rice bran soluble dietary fiber.(4)In this study,we used dialysis membrane combined with agitation to simulate the diffusion and absorption of glucose in the human intestine for further explore the effect of pretreatment on rice bran dietary fiber glucose diffusion and absorption.The results showed that glucose content in soluble dietary fiber dialysate extracted by extrusion and high hydrostatic pressure treatment was lower than that of untreated rice bran dietary fiber.In other words,the soluble dietary fiber extracted by extrusion and high hydrostatic pressure treatment assisted glucose in the process of dialysis is greater than the glucose-binding ability of untreated rice bran dietary fiber.It was investigated that pretreatment had a significant effect on the ability to bind cholesterol according to rice bran dietary fiber adsorption of cholesterol by amount of change before and after pretreatment.Soluble dietary fiber is more effective than insoluble dietary fiber in lowering serum cholesterol levels at the same time.Rice bran dietary fiber supplemented liquid hot water pretreatment assisted enzyme hydrolysis had higher ability to bind sodium cholate.Moreover,the ability of rice bran dietary fiber combined with sodium cholate to be suppressed by extrusion and high hydrostatic pressure treatment was low.Rice bran dietary fiber structure contains active groups,such as uronic acid,phenolic acid and amino acids,especially phenolic acid groups,which had a strong adsorption effect on nitroso groups.The pretreatment-assisted extraction of rice bran soluble dietary fiber contains high levels of phenolic acids belongs to free phenols,which can be easily exert its physiological activity in vivo.The content of phenolic acids in rice bran insoluble dietary fiber was not as much higher as that of rice bran soluble dietary fiber.Therefore,the clearance rate of NO2-was not as high as that of rice bran soluble dietary fiber.In summary,the pretreatment-assisted enzymatic hydrolysis of rice bran insoluble dietary fiber had a higher NO2-clearance rate than without pretreatment.(5)It was revealed that the main effect of rice bran on antioxidant activity is total phenols.In this paper,the total phenolic content was increased compared with extrusion and high hydrostatic pressure treatment.But it did not change significant after liquid hot water pretreatment.DPPH radical scavenging ability and FRAP Iron ion reduction capacity of rice bran were improved with extrusion,high hydrostatic pressure treatment and liquid hot water pretreatment.The scavenging capacities of rice bran was extrusion,high hydrostatic pressure treatment and liquid hot water pretreatment.The results showed that the change of rice bran antioxidant activity was mainly caused by the total phenolic content.Sucrose is the main component of dietary fiber which extracted by pretreatment assisted enzymatic hydrolysis followed by fructose and glucose.The highest content of soluble solids under the extrusion treatment conditions was followed by high hydrostatic pressure treatment and liquid hot water pretreatment.The lowest content of soluble solids of rice bran was without any treatment.As a good antioxidant source,rice bran dietary fiber can inhibit oxidation of lipids very well on the process of agricultural products processing and food storage.