【作者】 王旭；

【导师】 徐杨；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2018， 博士

【摘要】 米糠,作为稻米谷物深加工的高附加值副产品,因其含有丰富的膳食纤维、氨基酸以及人体必需生理活性成分和营养物质,越来越受到人们的青睐和重视。米糠中的主要成分,膳食纤维因具有较好的理化及功能特性,更是近年来研究的热点。然而,我国对米糠膳食纤维的研究仍处于起步阶段,存在米糠膳食纤维提取率相对较低,提取工序繁琐,化学制剂容易引入以及无法大批量生产等问题。因此,本研究以新鲜米糠为原料,选用三种不同的预处理方法,即挤压膨化、水热预处理及超高压处理辅助提取米糠膳食纤维,旨在提高米糠膳食纤维提取率,优化膳食纤维改性提取工艺。同时,探寻不同预处理的作用机理及其对预处理辅助提取的米糠膳食纤维成分、结构、理化性质、功能特性及抗氧化活性的影响。研究内容和结果如下:(1)挤压膨化辅助提取米糠可溶性膳食纤维最优工艺条件:当挤压温度为130℃、物料含水量为20%、螺杆速度200 r/min,α-淀粉酶含量2.0%、酶解反应时间90 min、酶解反应温度75℃、pH 6.0时,得到的米糠可溶性膳食纤维提取率最高,可达30.35%。米糠不溶性膳食纤维最优提取工艺条件:在挤压温度为130 ℃、物料含水量20%、螺杆速度200 r/min,反应提取温度50 ℃、料液比1:55、提取时间60 min、碱浓度0.25 mol/L的条件下,米糠不溶性膳食纤维提取率最高,可达 56.21%。(2)超高压辅助酶解提取米糠膳食纤维的最优工艺条件:超高压处理时间15 min,超高压处理压力400 MPa,超高压处理料液比为1:15。水热处理辅助酶解提取米糠膳食纤维工艺是:水热反应时间20 min、反应温度200 ℃。与未经预处理提取的米糠膳食纤维相比,挤压膨化处理对米糠可溶性膳食纤维及不溶性膳食纤维的理化性质影响最大,超高压处和水热处理次之。扫描电镜显示,预处理辅助提取的米糠膳食纤维其表面呈现疏松、蜂窝颗粒状,内部营养成分达到熔融状态,利于人体进一步地消化、吸收,物化特性得到明显改善。差示扫描热量和红外光谱分析显示,预处理未改变膳食纤维的降解机理,热力学相对稳定。米糠膳食纤维具有典型的糖类特征吸收峰,预处理辅助提取的膳食纤维特征吸收峰峰形、位置未发生明显变化,但预处理使纤维分子链间氢键被打断,多酚结构暴露,产生较多羧基。(3)预处理辅助提取的米糠膳食纤维吸附葡萄糖能力高于米糠原料,能有效降低小肠中的葡萄糖浓度。挤压辅助提取的可溶性膳食纤维葡萄糖透析延迟指数值最大,其次为超高压处理,水热处理对提高葡萄糖透析延迟指数值无显著作用。挤压和超高压辅助提取的可溶性膳食纤维透析液中,葡萄糖含量均低于未经处理的膳食纤维,预处理辅助提取的膳食纤维对葡萄糖的束缚力高于未处理的膳食纤维。预处理对米糠膳食纤维结合胆固醇的能力有明显影响,尤其是在降低血清胆固醇方面,可溶性膳食纤维相较不溶性纤维在降低胆固醇方面效果更佳。水热辅助提取的米糠膳食纤维结合胆酸钠的能力较强,挤压和超高压辅助提取的膳食纤维结合胆酸钠的能力较低。(4)预处理辅助提取的米糠可溶性膳食纤维含有较高含量的酚酸类物质,且都为游离酚类,易在体内发挥其生理活性作用。米糠不溶性膳食纤维中的酚酸含量不如米糠可溶性膳食纤维高,因此对NO2-的清除率不如米糠可溶性膳食纤维高。预处理辅助酶解提取的米糠不溶性膳食纤维对NO2-的清除速率和清除率高于未经预处理提取的米糠膳食纤维。(5)米糠中对抗氧化活性起主要作用的是总酚,挤压膨化处理、超高压处理与未经预处理的米糠相比,总酚含量有所提高,而米糠经水热处理后上述变化不显著。米糠经挤压膨化处理、超高压处理、水热处理过后,其铁离子还原能力以及DPPH自由基清除能力都有加强,其中,清除能力大小依次为:挤压膨化、超高压和水热处理。预处理辅助酶解提取的米糠膳食纤维中,包含蔗糖、果糖和葡萄糖等物质。其中,挤压预处理后得到的可溶性固形物最多,其次为超高压处理和水热处理,未经任何处理的米糠可溶性固形物含量最低。作为良好的抗氧化剂,米糠膳食纤维在农产品加工和食品贮藏过程中均能较好地抑制脂质的氧化。更多还原

【Abstract】 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.更多还原