大米分离蛋白的酶法提取及其性质

本文研究了以糖渣为原料,用淀粉酶法水解法制备大米分离蛋白(E-RPI)的反应条件,并测定了蛋白质的溶解性、乳化性及其氨基酸组成。结果表明,反应中固液比为1:12.96、加酶量为0.096％、反应时间为2.3h时效果最好,使糖溶出量达到原料重量的25.7％,产物中的蛋白含量为88.6％,回收率为90.5％;E-RPI的乳化活性随pH值的升高而增大,与大豆蛋白相比,乳化活性低而稳定性高。E-RPI中除赖氨酸外,其它必需氨基酸的含量均高于大豆蛋白和酪蛋白。     

碱法分离大米蛋白质和淀粉的工艺研究

大米蛋白质中80％以上是碱溶性谷蛋白，可采用碱提酸沉的方法分离大米蛋白质。本实验研究得到碱法分离大米蛋白质的最佳工艺条件为：碱液质量分数为0．3％，提取时间为4h，提取温度为室温，料液比为1：6。可得到纯度为80．7％的大米分离蛋白，蛋白质提取率为87．46％，淀粉损失率为2．77％。     

可食性大豆分离蛋白成膜工艺研究

文章通过单因素试验对大豆分离蛋白的成膜性进行研究。结果表明：大豆分离蛋白浓度、增塑剂（甘油）、还原剂（Na2SO3）、交联剂（TG酶）对膜的性能有较大影响，最佳处理条件为：大豆分离蛋白5．0％、甘油1．5％、Na2SO3 0．1％、TG酶0．2％，大豆分离蛋白浓度对膜性能影响最大，其次是甘油含量，Na2SO3和TG酶的浓度对膜性能影响较小。     

碱法分离大米蛋白和淀粉工艺的优化及其产品功能性质研究

本文以籼米为原料，研究了碱法提取分离大米蛋白和淀粉的工艺，并对大米分离蛋白和大米淀粉的功能性质进行了研究。确定了碱法分离大米蛋白和淀粉的最佳工艺条件：氢氧化钠溶液浓度为0．075mol／L；提取时间6h：料液比1：7g／mL；温度40℃。该优化条件下可以得到纯度高于80％大米分离蛋白，蛋白提取率为86．23％，淀粉回收率为92．12％。所得大米分离蛋白溶解性、起泡性好，乳化性能欠佳。     

高纯度大米蛋白和淀粉的分离提取

高纯度的大米蛋白和大米淀粉可以作为大米综合利用的两个主产品，本研究采用碱法将大米蛋白和淀粉分离，研究表明最适提取条件是：NaOH求度0．05N，提取2h此条件下分离体系不受破坏，且大米蛋白的蛋白含量可达94.03％(干基)，蛋白得率63．37％；大米淀粉中蛋白含量0．39％(干基)，淀粉得率47．87%。     

大豆分离蛋白(SPI)乳化稳定性的研究

将有限酶解和Na2SO4预还原处理有机结合起来，对大豆分离蛋白进行改性，以研究中性环境中改性对大豆分离蛋白乳化稳定性的影响。由此确定改性条件，为调配型中性豆奶的研制奠定了基础。     

动态超高压微射流均质对大米蛋白功能特性的影响

以大米蛋白为原料,在不同料液比(1∶100~12∶100)和不同p H(2~12)的条件下,采用动态超高压微射流进行均质处理,研究不同均质压力(40~200 MPa)和均质次数(1~5次)对大米蛋白功能特性(溶解性、乳化性及稳定性、起泡性及稳定性和粘度)的影响。结果表明:不同料液比和不同p H的大米蛋白溶液经动态超高压微射流均质后其溶解性、起泡性、粘度均有显著的提高,而不同料液比和不同p H的大米蛋白溶液的起泡稳定性均无显著的提高。不同p H的固定料液比(3∶100)大米蛋白溶液经动态超高压微射流均质后其乳化性及稳定性有显著的改善,而不同料液比(尤其是料液比较高时)的固定p H(p H=7)大米蛋白溶液的乳化性及稳定性无显著性改善。均质压力对固定料液比(3∶100)和p H(p H=7)大米蛋白溶液的溶解性、乳化性及稳定性、起泡性、粘度的提高影响显著,而对其起泡稳定性无显著性作用。均质次数对固定料液比(3∶100)和p H(p H=7)大米蛋白溶液的溶解性、乳化性稳定性、起泡性及稳定性、粘度的提高影响显著,而对其乳化性无显著性作用(1~3次),甚至在均质次数较多(4~5次)时有负面性影响。      

大米蛋白质的酶法水解及其性质研究

本文通过三种蛋白酶催化反应动力学特性的比较，确定用碱性蛋白酶Alcalase作为水解大米分离蛋白的酶制荆，并通过正交试验分别获得高溶解性、高发泡性、高乳化性大米蛋白水解物的酶反应条件。本实验所得到的大米蛋白水解物最大溶解度为50．2％，最大发泡力为50mL，最大乳化力为73．6mL／g。     

棉籽分离蛋白功能性质的研究

考察了棉籽各分离蛋白,包括清蛋白、球蛋白、醇溶谷蛋白及谷蛋白在棉籽蛋白中所占的比例,研究了各蛋白的功能性质,包括吸水性、吸油性、乳化性和乳化稳定性、起泡性与泡沫稳定性以及各蛋白的抗氧化活性。结果表明,谷蛋白为棉籽蛋白中的主要分离蛋白,棉籽清蛋白具有较高的吸水性、乳化性、乳化稳定性以及起泡性,吸油性相对较差,适用性相对较好,但在棉籽蛋白中含量较少,而谷蛋白的吸水性、乳化性、起泡性很差,具有一定的吸油性,适用性较差,但在棉籽蛋白中含量丰富,在抗氧化活性方面,各分离蛋白的抗氧化活性能力都较差,需要进行改性处理。     

蛋白组分对米蛋白功能性质影响的研究

以不同配比米蛋白组分的样品为试材,比较各样品的功能性质变化,明确各蛋白组分对蛋白产品品质影响的差异,为今后进行分子设计和重组生产米蛋白产品提供理论支撑。通过各蛋白样品的溶解性,乳化特性,起泡特性,持水性/持油性等功能性质研究,结果表明,米糠浓缩蛋白的溶解性比大米浓缩蛋白高200%左右;米糠蛋白各功能性质显著优于大米蛋白,但大米蛋白的起泡稳定性比米糠蛋白提高近20%。米蛋白中的清蛋白提高产品的溶解性、持水性/持油性,降低起泡稳定性;醇溶蛋白提高产品的乳化特性;谷蛋白提高产品的起泡稳定性。蛋白产品的功能性质与蛋白组分的组成密切相关。     

Rice Protein Isolates Produced by the Two Different Methods Lower Serum Cholesterol Concentration in Rats Compared with Casein

Highly purified rice protein isolates (RPI) were prepared by an alkaline extraction–acid precipitation method (E-RPI) and by an α-amylase treatment to remove starch (T-RPI). Biological values of these RPI were significantly lower than that of casein. Serum cholesterol concentrations were compared among groups of rats fed (per kg diet) 200, 300 or 400 g E-RPI, 400 g T-RPI, 250 or 400 g casein kg⁻¹ or 400 g soya bean protein isolate (SPI). With all the diets containing 400 g protein kg⁻¹ diet, growth rates of rats were the same. At this level, E-RPI, T-RPI and SPI diets produced significantly lower serum cholesterol concentrations than the casein diet. Faecal bile acid plus neutral steroid excre-tion was significantly higher in rats fed the 400 g kg⁻¹ T-RPI or 400 g kg⁻¹ SPIdiets compared with rats fed the 400 g kg⁻¹ casein diet. On the other hand, the 400 g kg⁻¹ E-RPI diet did not increase steroid excretion. Plasma cholesterol concentrations in rats fed diets with amino acid mixtures simulating SPI and E-RPI were also significantly lower than that of rats fed the diet with an amino acid mixture simulating casein even though the faecal excretions of total bile acids were the same amongst groups. These results support the view that RPI are hypocholesterolaemic relative to casein and at least the hypocholesterolaemic effects of E-RPI would be independent of interruption of the enterohepatic circulation of endogenous steroids.     

Effect of acetylation and succinylation on solubility profile, water absorption capacity, oil absorption capacity and emulsifying properties of mucuna bean (Mucuna pruriens) protein concentrate

Mucuna protein concentrate was acylated with succinic and acetic anhydride. The effects of acylation on solubility, water absorption capacity, oil absorption capacity and emulsifying properties were investigated. The pH-dependent solubility profile of unmodified mucuna protein concentrate (U-mpc) showed a decrease in solubility with decrease in pH and resolubilisation at pH values acidic to isoelectric pH (pH 4). Apart from pH 2, both acetylated mucuna protein concentrates (A-mpc) and succinylated mucuna protein concentrate (S-mpc) had improved solubility over the unmodified derivative. Acylation increased the water absorption capacity (WAC) at all levels of ionic strength (0.1-1.0 M). WAC of the protein samples increased with increase in ionic strength up to 0.2 M after which a decline occurred with increase in ionic strength from 0.4-1.0 M. When protein solutions were prepared in salts of various ions, increase in WAC followed the Hofmeister series in the order: NaSCN < NaClO4 < NaI < NaBr < NaCl < Na2SO. Acetylation improved the oil absorption capacity while the lipophilic tendency reduced the following succinylation. Emulsifying capacity increased with increase in concentration up to 2, 4 and 5% w/v for U-mpc, A-mpc and S-mpc, respectively, after which an increase in concentration reduced the emulsifying capacity. Both acetylation and succinylation significantly (P < 0.05) improved the emulsifying capacity at pH 4-10. Initial increase in ionic strength up to 0.4 M for U-mpc and 0.4 M for A-mpc and S-mpc increased the emulsion capacity progressively. Further increase in ionic strength reduced emulsion capacity (EC). Contrary to the effect of various salts on WAC, increase in EC generally follows the series Na2SO4 < NaCl < NaBr < NaI < NaClO4 < NaSCN. At all levels of ionic strength studied, S-mpc had a better emulsifying activity (EA) than both A-mpc and U-mpc. EA and emulsifying stability (ES) were pH-dependent. Maximum EA and ES were recorded at pH 10. ES of protein derivatives were higher than those of U-mpc in the range of pH 4-10 but lower at pH 2. Studies revealed that both A-mpc and S-mpc had better ES and EA than the unmodified derivative when protein solutions were prepared in salts of various anions.     

Stability of model emulsions prepared using whey and muscle proteins

The amount of water (SW) and oil (SO) separated from model emulsions and emulsion stability (ES) of these emulsions prepared from corn oil and of fluid whey, total muscle protein (TMP), whey + TMP and sarcoplasmic protein (SP) were examined. The SW value of whey + TMP emulsions was lower (26,33%) than that of TMP (31,33%), SP (39,0%) practically the same as that of whey only. However, the SO value of whey emulsions was higher (9,40%) than that of muscle protein emulsions (0,0%). It was found that there was no oil separation in whey + TMP emulsions. Whey proteins had the lowest ES (64,6 ± 0,96) among the proteins studied. Nevertheless, whey + TMP emulsions had the highest ES (73,67 ± 0,58).     

pH and Sodium Chloride Effects on Emulsifying Properties of Egg Yolk Phosvitin

The emulsifying properties of phosvitin dissolved in water and 0.1, 0.5 and 1.0 M NaCl were determined from pH 3 to 10. The change in its emulsifying activity (EA) with pH was slight but significant (p<0.05) and emulsion stability (ES) was relatively high (68-73%), except at pH 5 (17%) and 10 (48%). The EA of phosvitin was higher than that of bovine serum albumin (BSA) at pH 3 or 8 and ES was higher than BSA at all pH levels except at pH 5 and 10. Added NaCl decreased in the EA of phosvitin at pH 3 and 10 and decreased the ES between pH 3 and 9. Increased instability of emulsions resulted mainly in coalescence of oil droplets at NaCl ≥ 0.5M. Salt increased the viscosity of phosvitin emulsion only at pH 3 but not at pH > 5. The viscosities of BSA emulsions were higher than those of phosvitin at pH 3, 5 or 8.     

Improvement of the solubility and emulsification of rice protein isolate by the pH shift treatment

In the current research, we have adopted a pH shift treatment method that can significantly improve the solubility and emulsification of rice protein isolate (RPI) under neutral conditions. Our results showed that the RPI reached a quasi-equilibrium state at 1 h after alkali shift treatment, and the solubility and emulsifying properties of RPI were significantly improved compared with the control. In addition, the particle size of RPI decreased considerably under the alkali shift treatment. The results of electron microscopy showed that the RPI aggregates were depolymerised and the particle size distribution was more uniform. The pH shift treatment induced the rearrangement of protein secondary structure, and the exposure of hydrophobic groups increase the surface hydrophobicity of RPI. The change in endogenous fluorescence spectrum, UV and the disulfide bond content all showed that the conformation of RPI changed significantly through pH shift treatment. In addition, it was found that the RPI treated under pH 10–11 shift possessed the best property to stabilise the emulsion. This study showed that under the condition of pH10 and pH11 shift treatment, the structural and functional properties of RPI were vastly improved, and the application of RPI in food was greatly ameliorated.     

凯氏定氮法测定大米蛋白质时蛋白系数的确定

本文通过对10个不同来源大米蛋白粉样品氨基酸成分的分析,计算出17种氨基酸含氮量平均值为13.48%,标准差S为0.19,变异系数CV为1.2%,表明重复性很好。通过对天冬酰胺和谷氨酰胺含量范围的设定计算出大米蛋白含氮量变化范围为13.48%～15.78%,即蛋白系数在6.34～7.41之间;进一步通过对高纯度蛋白质样品全成分的分析,确定大米蛋白质的蛋白系数为6.70。经验证计算结果更符合真实情况。     

High pressure versus heat treatments for pasteurisation and sterilisation of model emulsions

Heat treatments can have considerable influence on the droplet size distribution of oil-in-water emulsions. In the present study, high-pressure (HP) pasteurisation and sterilisation were evaluated as alternatives for heat preservation of emulsions. HP conditions used were 600 MPa, 5 min, room temperature and 800 MPa, 5 min, 80 °C initial temperature, 115 °C maximum temperature for HP pasteurisation and HP sterilisation respectively. The effects on droplet size of these conditions were compared to heat treatments for whey protein isolate (WPI) and soy protein isolate (SPI) emulsions at two pH values and two ionic strengths. For WPI, also the effect of protein in the bulk phase was evaluated.Both HP and heat pasteurisation treatments resulted in similar or slightly decreased average droplet sizes compared to the untreated samples. For neutral SPI emulsions, heat sterilisation increased the average droplet size from 1.6 μm to 43.7 μm, while HP sterilisation resulted only in a small increase towards an average droplet size of 2.1 μm. The neutral WPI emulsions, except those with a high ionic strength, gave similar results with respect to the droplet size, showing that for neutral pH WPI or SPI emulsions HP sterilisation is preferable above heat sterilisation. Concerning the low pH WPI emulsions, the droplet sizes were unaffected after both heat and HP sterilisation.Industrial relevanceHeat pasteurisation and sterilisation are effective treatments to preserve food products that are based on emulsions with respect to microbial safety. However, heat treatments can negatively affect emulsion stability. Currently, in addition to high pressure at room temperature, high-pressure treatments at elevated temperature received a great deal of interest to achieve sterilised products. This study evaluated the effects of both heat and high-pressure pasteurisation and sterilisation on droplet size of whey protein isolate and soy protein isolate emulsions. It was shown that for pasteurisation treatments, both heat and high pressure have minor effects on the droplet size of the emulsion. However, for sterilisation purposes high-pressure treatment is preferable for emulsion at neutral pH. High-pressure sterilisation can therefore be interesting alternatives to heat treatments to preserve emulsion stability.     

鸭血糯蛋白的提取及功能性研究

采用碱溶酸沉法制备鸭血糯分离蛋白,并对其氨基酸组成和功能性质进行检测。结果表明,鸭血糯总蛋白含量为8.72%。鸭血糯分离蛋白得率为4.63%,纯度为65.8%。鸭血糯氨基酸组成均衡,其中谷氨酸含量最高,半胱氨酸含量最低。鸭血糯分离蛋白表面疏水性为114,二硫键含量15.1μmol/g,吸油能力、乳化性较好,起泡性稍差。1%~10%的鸭血糯分离蛋白添加量对鱼糜制品的凝弹性、品质等无显著影响。可考虑鸭血糯蛋白在各类食品中添加应用。     

预热处理对乳清分离蛋白水包油乳状液特性和物理稳定性的影响

本实验主要研究了加热预处理（90℃,5 min）对乳清分离蛋白作为稳定剂所制备的菜籽油水包油型乳状液的特性和物理稳定性的影响。测定了乳状液在储藏期间的ζ-电势、粒径、絮凝指数、分层指数、流变特性和乳状液中蛋白质分配系数的变化趋势。研究结果表明,与天然乳清分离蛋白相比,经过预热处理的乳清分离蛋白能够显著降低乳状液在整个储藏期间（0¹4 d）的物理稳定性（p<0.05）,具体表现为较低的ζ-电势（p<0.05）,以及较高的粒径、絮凝指数、分层指数和粘度（p<0.05）。与此同时,加热处理导致的乳清分离蛋白变性和聚集,能够显著增加其在乳状液界面蛋白膜表面的分布（p<0.05）,从而验证了上述乳状液物理稳定性的结果。上述结果表明,加热预处理显著降低了整个乳状液在储藏期间的物理稳定性,为乳清分离蛋白在乳状液中的合理应用奠定了理论基础。