挤压稳定化处理对米糠各组分蛋白结构及功能性质的影响

为了研究挤压稳定化处理对米糠各组分蛋白结构和功能性质的影响,选取龙粳31号大米米糠做为原料,采用双螺杆挤压技术对该原料进行稳定化处理。结果表明：米糠各组分蛋白在挤压处理后溶解性、起泡性和持油性显著降低（P?0.05）,持水性、起泡稳定性和乳化稳定性升高,谷蛋白持水性提高的幅度最大,较挤压前提高了39%。米糠谷蛋白的乳化活性与其他两种组分蛋白差异显著,清蛋白和球蛋白较挤压前分别降低5%和10%,谷蛋白乳化活性增加,较挤压前增加8%。结构特性分析结果表明产生这种差异的主要原因不是分子间作用力,而是挤压后各组分蛋白发生重组,形成大的聚集体过程中二级结构的变化截然相反,米糠清蛋白α-螺旋、β-转角和无规则卷曲含量都有所降低,β-折叠含量增势明显提高。挤压后的米糠谷蛋白结构与白蛋白显示出不同的趋势,谷蛋白的二级结构在酰胺I带变化显著,α-螺旋、β-转角与无规则卷曲的含量有所提高,β-折叠的含量下降。结果可为米糠各组分蛋白的工业化制备及在各种食品配方中的应用提供理论支撑。     

Preparation and functional properties of rice bran protein isolate

Rice bran protein isolate (RBPI) containing approximately 92.0% protein was prepared from unstabilized and defatted rice bran using phytase and xylanase. The yield of RBPI increased from 34% to 74.6% through the use of the enzymatic treatment. Nitrogen solubilities of RBPI were 53, 8, 62, 78, 82, and 80% at pHs 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0, respectively. Differential scanning calorimetry showed that RBPI had denaturation temperature of 83.4 degrees C with low endotherm (0.96 J/g of protein). RBPI had similar foaming properties in comparison to egg white. But emulsifying properties of RBPI were significantly lower than those of bovine serum albumin. The result of amino acid analysis showed that RBPI had a similar profile of essential amino acid requirements for 2-5-year-old children in comparison to that of casein and soy protein isolate.     

Purification and identification of components of gamma-oryzanol in rice bran Oil.

High-purity gamma-oryzanol was obtained from crude rice bran oil using a normal-phase preparative scale HPLC. A reverse-phase HPLC method was used for separating the individual components of gamma-oryzanol present in rice bran oil. Ten fractions were isolated and collected using the reverse-phase HPLC method, and their structures were identified. Identification was accomplished using GC/MS with an electron impact mass spectrum after components were transformed into trimethylsilyl ether derivatives. The 10 components of gamma-oryzanol were identified as Delta(7)-stigmastenyl ferulate, stigmasteryl ferulate, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, Delta(7)-campestenyl ferulate, campesteryl ferulate, Delta(7)-sitostenyl ferulate, sitosteryl ferulate, compestanyl ferulate, and sitostanyl ferulate. Three of these, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate, were major components of gamma-oryzanol.     

Quantification of vitamin E and gamma-oryzanol components in rice germ and bran

Rice bran is a rich natural source of vitamin E and gamma-oryzanol, which have been extensively studied and reported to possess important health-promoting properties. However, commercial rice bran is a mixture of rice bran and germ, and profiles of vitamin E and gamma-oryzanol components in these two different materials are less well-studied. In the current study, vitamin E and gamma-oryzanol components in rice bran and germ were analyzed by liquid chromatography/mass spectrometry/mass spectrometry. The components were identified by electrospray ionization mass spectrometry (ESI-MS) with both positive- and negative-ion modes. Both deprotonated molecular ion [M - H](-) and protonated molecular ion [M + H](+) found as the base peaks in spectra of vitamin E components made ESI-MS a valuable analytic method in detecting vitamin E compounds, especially when they were at very low levels in samples. Ultraviolet absorption was used for quantification of vitamin E and gamma-oryzanol components. While the level of vitamin E in rice germ was 5 times greater than in rice bran, the level of gamma-oryzanol in rice germ was 5 times lower than in rice bran. Also, the major vitamin E component was alpha-tocopherol in rice germ and gamma-tocotrienol in rice bran. These data suggest that rice bran and germ have significantly different profiles of vitamin E and gamma-oryzanol components. The method enables rapid and direct on-line identification and quantification of the vitamin E and gamma-oryzanol components in rice bran and germ.     

亚临界丙烷萃取米糠油及其微量活性组分动力学模型

为了揭示亚临界流体萃取米糠油及其微量活性组分的动力学规律,该文以亚临界丙烷为萃取介质,研究了米糠油、γ-谷维素及α-生育酚等活性组分在不同萃取温度和时间的萃取率,并基于 Baümler 模型对目标物的萃取率进行模型拟合,建立相应的动力学模型并验证。结果表明,亚临界萃取过程中目标物的相对萃取率随时间增长递增,且在初始阶段（洗涤过程）的增长速率快于第二阶段（扩散过程）的增长速率;同时,升高萃取温度可同时提高目标产物的扩散系数和相对萃取率;基于Baümler模型可较好拟合亚临界丙烷萃取米糠油、γ-谷维素和α-生育酚的动力学过程（R2>0.95）,所得动力学模型具有较好的预测准确性。由Arrhenius方程可计算出米糠油、α-生育酚和γ-谷维素的亚临界萃取反应活化能,其中米糠油的活化能最低（5.23 kJ/mol）,α-生育酚次之（7.05 kJ/mol）,γ-谷维素最高（9.11 kJ/mol）,表明γ-谷维素最难萃取且对温度依赖程度最高;根据拟合所得动力学模型,对米糠油提取率进行预测,结果表明,该模型对米糠油萃取率的预测准确率达95.8%,而对γ-谷维素和α-生育酚萃取率的预测准确度稍低,分别达94.7%和94.4%,对三者均具有很好的预测准确性。总之,基于 Baümler 模型可以较好地建立米糠油及其有益伴随物的亚临界萃取动力学模型,从而较为准确的预测米糠油及其微量活性组分的萃取率,对米糠油的亚临界萃取工艺具有一定的理论指导意义。     

Optimization of acid hydrolysis conditions for feruloylated oligosaccharides from rice bran through response surface methodolgy

Response surface methodology (RSM) was employed to optimize the hydrolysis conditions with trifluoroacetic acid (TFA) to obtain the maximum amount of feruloylated oligosaccharides from rice bran. The TFA concentration and hydrolysis time effects on feruloylated oligosaccharides recovery are studied. The optimum hydrolysis conditions for maximizing feruloylated oligosaccharides recovery were 193 mM TFA concentration and 1.36 h of hydrolysis time. Under these conditions the corresponding acyl ferulic group quantity was 78.63 microg in 1 mL of hydrolysate. The model was experimentally verified with a satisfactory coefficient of R (2) (= 0.96). The quantity of acyl ferulic group in the feruloylated oligosaccharides, purified using Amberlite XAD-4, was 916.12 microg/g of rice bran under the optimum hydrolysis conditions. The proposed method accounted for 54.08% of the total acyl ferulic group in rice bran. The results suggest that the proposed conditions were useful in maximizing recovery of feruloylated oligosaccharides from rice bran.     

复合酶法提取稻麸蛋白工艺的优化

运用配料试验设计,采用纤维素酶、复合蛋白酶、植酸酶提取米糠分离蛋白,建立复合酶配合比例与蛋白得率之间的数学模型,确定最佳配比为：纤维素酶65.84%、蛋白酶18.52%、植酸酶15.64%,最佳反应条件为：复合酶温度45℃、底物浓度 20%、酶添加量4%、pH值5.5、水解时间2 h,最终蛋白收率可达86%以上。     

燕麦麸分离蛋白的酶解对其功能性质的影响

为了改善燕麦蛋白的功能性质以扩大其在食品工业中的应用,该文以燕麦麸为原料制备了燕麦麸分离蛋白(OBPI),并利用胰蛋白酶对其进行水解,得到了3种不同水解度(4.1%、6.4%、8.3%)的酶解产物。SDS-PAGE分析结果表明OBPI中的主要蛋白成分是球蛋白,其经过胰蛋白酶处理后,球蛋白酸性亚基被部分水解而碱性亚基相对保持完整。胰蛋白酶水解显著改变了OBPI的功能性质。在所考察的水解度范围内,随着水解度的升高,酶解产物的溶解性、持水性、乳化活性及起泡能力等方面均逐渐增加;但持油性、乳化及泡沫稳定性有不同程度的降低。     

碱酶两步法制备大米蛋白的研究

该文采用碱法和酶法两步加工碎米,制备得到纯度较高的大米蛋白。通过研究米粉粒度、pH值、温度、水料比和时间对提取率的影响,确定碱法制备大米蛋白的较佳工艺条件为：米粉粒度80目,pH 11.0,温度50℃,水料比8,时间120 min。采用α-淀粉酶对大米蛋白进行纯化,酶解条件为：加酶量60 U/g,pH 6.0,温度50℃,时间30 min。在上述工艺条件下制备大米蛋白,提取率为73.22%,纯度为88.75%。     

大米降压肽酶法制备工艺及其性质研究

该文利用碱性蛋白酶水解大米蛋白制备大米降压肽，确定碱性蛋白酶水解终点为水解度18.17%。采用9种大孔吸附树脂吸附大米降压肽，结果显示NKA型树脂对大米降压肽的吸附效果较好，大米降压肽中灰分含量由脱盐前的16.64%减少到脱盐后的2.32%。对大米降压肽的相对分子质量、溶解性进行分析，大米降压肽的相对分子质量在138～1461之间；在pH 3～11的范围内，大米降压肽的溶解度在97.6%左右。     

Functional properties of protein isolates extracted from stabilized rice bran by microwave, dry heat, and parboiling

Protein isolates extracted from differently stabilized rice bran were analyzed to work out the food use potential. Bulk density remained higher for isolates obtained from heat stabilized bran, the treatments were found to have positive impact on the oil absorption properties, while the water absorption was slightly impaired owing to some possible configurational changes. Surface hydrophobicity and emulsion properties were improved with bran stabilization. Isolates exhibited better foaming properties owing to the flexible nature of protein molecules, with less intensive disulfide bonding, that were slightly affected by the stabilization treatment. Nitrogen solubility index followed a curved pattern with the least value near isoelectric point that showed an increasing trend toward basic pH, and parboiled protein isolates exhibited better gelling properties among the isolates.     

Properties of extracts from defatted rice bran by its subcritical water treatment

Defatted rice bran was extracted with water and subcritical water at 50-250 degrees C for 5 min. The highest extract yield was achieved at 200 degrees C, at which the maximum amounts of protein and carbohydrate were also obtained. The total phenolic and furfural contents, radical scavenging activity, and antioxidative activity for the autoxidation of linoleic acid increased with increasing treatment temperature. The bran extracts exhibited emulsifying activity except for the extract prepared at 250 degrees C, which was concomitant with the disappearance of its high-molecular-mass substances. The extract prepared at 200 degrees C also had the highest emulsion-stabilizing activity.     

高酸值米糠油酯化脱酸成生物柴油原料

为充分利用高酸值米糠毛油,将其脱酸成生物柴油原料。采用酯化脱酸方法,通过对多种酯化脱酸催化剂的比较,结果表明氧化锌具有较强的催化活性。氧化锌作为米糠油酯化脱酸的催化剂,分别考察了甘油添加量、催化剂添加量、反应温度、反应时间对酯化脱酸的影响。得到了以下较优工艺参数：真空度为0.1 MPa,甘油添加量为理论甘油量1.044 g,催化剂添加量为油质量的0.1%,反应温度200℃,反应时间6 h。在此优化条件下,米糠油的酸值从38.14 mg/g降至5.17 mg/g,满足了作为生物柴油生产原料的要求。     

Antioxidant activity of tocopherols, tocotrienols, and gamma-oryzanol components from rice bran against cholesterol oxidation accelerated by 2,2'-azobis(2-methylpropionamidine) dihydrochloride

The antioxidant activities of vitamin E (alpha-tocopherol, alpha-tocotrienol, gamma-tocopherol, and gamma-tocotrienol) and gamma-oryzanol components (cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate) purified from rice bran were investigated in a cholesterol oxidation system accelerated by 2,2'-azobis(2-methylpropionamidine) dihydrochloride. All components exhibited significant antioxidant activity in the inhibition of cholesterol oxidation. The highest antioxidant activity was found for 24-methylenecycloartanyl ferulate, and all three gamma-oryzanol components had activities higher than that of any of the four vitamin E components. Because the quantity of gamma-oryzanol is up to 10 times higher than that of vitamin E in rice bran, gamma-oryzanol may be a more important antioxidant of rice bran in the reduction of cholesterol oxidation than vitamin E, which has been considered to be the major antioxidant in rice bran. The antioxidant function of these components against cholesterol oxidation may contribute to the potential hypocholesterolemic property of rice bran.     

Lipase-catalyzed modification of rice bran oil to incorporate capric acid

Capric acid (C10:0) was incorporated into rice bran oil with an immobilized lipase from Rhizomucor miehei as the biocatalyst. Effects of incubation time, substrate mole ratio, enzyme load, and water addition on mole percent incorporation of C10:0 were studied. Transesterification was performed in an organic solvent, hexane, and under solvent-free condition. Pancreatic lipase-catalyzed sn-2 positional analysis and tocopherol analysis were performed before and after enzymatic modification. Products were analyzed by gas-liquid chromatography (GLC) for fatty acid composition. After 24 h of incubation in hexane, there was an average of 26.5 +/- 1.8 mol % incorporation of C10:0 into rice bran oil. The solvent-free reaction produced an average of 24.5 +/- 3.7 mol % capric acid. In general, as the enzyme load, substrate mole ratio, and incubation time increased, the mole percent of capric acid incorporation also increased. Time course reaction indicated C10:0 incorporation increased up to 27.0 mol % at 72 h, for the reaction in hexane, and up to 29.6 mol % at 12 h, for the solvent-free reaction. The highest C10:0 incorporations (53.1 and 43.2 mol %) for the mole ratio experiment occurred at a mole ratio of 1:8 for solvent and solvent-free reactions, respectively. The highest C10:0 incorporation (27.9 mol %) for the reaction in hexane occurred at 10% enzyme load, and the highest incorporation (34.4 mol %) for the solvent-free reaction occurred at 20% enzyme load. Incorporation of C10:0 into rice bran oil declined with the addition of increasing amounts of water after reaching 30.3 mol % at 2% water addition in hexane, and in the solvent-free reaction after reaching 35.9 mol %.     

Prevention of oxidative rancidity in rice bran during storage.

The effect of microwave heat on lipoxygenase (LOX) activity in rice bran under various storage conditions was examined. Raw rice bran from the long-grain variety Lemont was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran samples were packed in zipper-top bags or vacuum packs and stored at room temperature (25 degrees C) or in the refrigerator (4-5 degrees C) for 16 weeks. Samples were analyzed for LOX activity at 4-week intervals. LOX activity did not significantly change from its initial value at week 0 for zipper-top and vacuum-packed samples while stored at 4-5 degrees C for 12 weeks, but decreased at week 16. Vacuum packing did not show a significant impact on LOX activity during 16 weeks of storage. Microwave-heated samples stored in the refrigerator did not show significant change in LOX activity for up to 12 weeks but showed a significant (p < 0. 05) decrease at 16 weeks. Results showed that oxidative rancidity of rice bran could be prevented by microwave heating the samples, packing in zipper-top bags, and storing at 4-5 degrees C for up to 16 weeks.     

Prevention of hydrolytic rancidity in rice bran during storage.

The effect of microwave heating, packaging, and storage temperature on the production of free fatty acids (FFA) in rice bran was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran were packed in zipper-top bags or vacuum-sealed bags and stored at 4-5 or 25 degrees C for 16 weeks. FFA content of bran was measured at 4-week intervals. Total FFA increased rapidly over the 16-week period from the initial value of 2.5% in raw bran stored at 25 degrees C to 54.9% in vacuum bags and 48.1% in zipper-top bags. However, total FFA of raw bran stored at 4-5 degrees C increased at a slower rate from an initial value of 2. 5 to 25.4% in vacuum bags and 19.5% in zipper-top bags. After 16 weeks of storage, total FFA of microwave-heated bran stored at 25 degrees C increased from 2.8 to 6.9 and 5.2%, respectively, for samples stored in vacuum bags and zipper-top bags. Total FFA of microwave-heated samples stored at 4-5 degrees C did not change significantly with storage time. Results showed that hydrolytic rancidity of rice bran can be prevented by microwave heating and that the recommended storage condition for microwaved rice bran is 4-5 degrees C in zipper-top bags.     

大米肽的酶法制备工艺及其特性的研究

该文利用蛋白酶水解大米蛋白制备得到大米肽。比较碱性蛋白酶、中性蛋白酶、复合蛋白酶和风味酶水解大米蛋白的进程曲线,结果显示碱性蛋白酶的水解效果最好,其较佳作用条件为：底物浓度10%、pH值9.0、温度45℃、酶与底物比48 AU/kg、时间150 min。在此条件下,大米肽的得率为46.8%,纯度为71.3%。大米肽具有溶解性较好和黏度较低的特性,可以在食品中广泛应用。     

羊奶乳清蛋白水解物的酶解制备

采用Alcalase与Flavourzyme两种酶对羊奶乳清蛋白进行水解,以水解度为指标,对两种酶单独使用及复合使用水解羊奶乳清蛋白的工艺条件进行了研究。试验结果显示:采用Alcalase与Flavourzyme复合水解羊奶乳清蛋白的效果较好,特别是采用先添加Flavourzyme后加入Alcalase进行水解,不仅能提高羊奶乳清蛋白的水解度,使其达到32.81%,而且对改善水解液的口感有较大的作用。