右旋糖苷修饰玉米SOD研究

为提高玉米SOD的稳定性,利用右旋糖苷对玉米SOD进行修饰.在不同条件下测定玉米SOD的活力,比较修饰前后玉米SOD稳定性.结果表明:修饰后玉米SOD的活性保持率为83%,修饰后玉米SOD的温度稳定性、pH稳定性均有显著提高,半衰期延长,对胃蛋白酶、胰蛋白酶耐受性增强.说明右旋糖苷是一种较好的玉米SOD化学修饰剂.     

生姜蛋白酶的大分子结合修饰

采用单甲氧基聚乙二醇(mPEG)和右旋糖苷对生姜蛋白酶进行大分子结合修饰。在酶液质量浓度为2.0mg/mL的硼酸缓冲液中,加入三聚氯氰活化的mPEG 或高碘酸钠活化的右旋糖苷,于40℃修饰反应1h,对修饰剂与酶蛋白的质量比和pH 值条件进行优化：mPEG 与酶的质量比为17.5:1.0、pH9.0,mPEG 修饰酶的修饰率为52.6%,相对酶活力(修饰酶活力/ 天然酶活力)为54.0%;右旋糖苷与酶的质量比为42:1、pH6.0,右旋糖苷修饰酶的修饰率为51.6%,其相对酶活力为原天然酶的3.3 倍。两种修饰酶的热稳定性均比天然酶显著增强,且右旋糖苷修饰酶的热稳定性明显高于mPEG 修饰酶。结果表明：右旋糖苷对生姜蛋白酶的修饰效果优于聚乙二醇,适用于酶蛋白的化学修饰与新型酶制剂的开发利用。     

右旋糖苷对超氧化物岐化酶的化学修饰及性质研究

采用高碘酸钠活化右旋糖，对豌豆SOD进行化学修饰，得到右旋精──SOD的加合物。实验结果表明，该修饰酶不仅保留了天然酶的活性，而且在耐热性，耐酸性和胃蛋白酶水解能力等方面都优于天然酶。修饰酶较天然酶稳定，具有较高的实用意义。     

沙棘SOD结构修饰及性质研究

研究沙棘SOD纯化和化学修饰的效果。用沙棘原果为材料,经透析膜进行纯化SOD,选用月桂酸对沙棘SOD进行化学修饰,最后分别对天然SOD和修饰后SOD做热稳定性、抗酶解性、抗酸碱性和金属离子影响的研究。研究结论表明:修饰后SOD的热稳定性与pH稳定性均明显提高。与天然SOD相比,修饰后的蛋白酶酶切耐受性明显增强,同时金属离子对修饰后的SOD影响也较天然SOD不同。     

玉米SOD的纯化与化学修饰

本文利用硫酸铵分级沉淀、凝胶过滤初步分离了玉米SOD,利用金属螯合亲和层析纯化了SOD。比活为8597,纯化倍数为307,回收率为29.4%,电泳后活性染色与蛋白染色均得到3个条带,达到了电泳纯。针对SOD稳定性较差的缺陷,进行了PEG修饰SOD研究。修饰率46%,SOD活性保持度为81%。修饰后的玉米SOD的温度稳定性、pH稳定性均明显提高,与天然SOD相比,PEG-SOD的胰蛋白酶酶切耐受性明显增强。结果表明,PEG修饰玉米SOD是可行的,PEG是一种较好的SOD化学修饰剂。     

右旋糖苷蔗糖酶的研究进展

右旋糖苷蔗糖酶(dextransucrase)是一种典型的葡萄糖基转移酶,可利用蔗糖为底物合成右旋糖苷,而后者在医药、食品等领域用途广泛。从酶的来源、产量优化、制备方法和活性检测的角度总结右旋糖苷蔗糖酶的研究进展,并对其发展趋势进行的展望。     

采用当地分离出肠粘膜状明串珠菌从蔗糖制备右旋糖苷及其特性

人们很久就知道了细菌多糖,右旋糖苷。它是由五个D—葡萄糖残基重复结合而成的分支聚合物。右旋糖苷的分子量为高,其分子量大小赖于菌种和制备方法。工业上采用右旋糖苷的分子量可达到40,000,000,但可以用酸或酶降解成低分子量片断。已知它在药物上和食品工业上有很多用途。经部分水解或降解的右旋糖苷可用作血浆体积溶胀剂。低分子右旋糖苷铁络合物可用来治疗缺铁贫血症。也可以制备具有不寻常的高粘度的无结晶糖浆。也可以部分代替大麦芽。     

细菌右旋糖酐蔗糖酶研究进展

从右旋糖苷蔗糖酶的分类、酶学性质、分离纯化、基因结构及蛋白质组成等方面综述了右旋糖苷蔗糖酶的研究动态.     

超氧化物歧化酶（SOD）的微胶囊化

针对SOD稳定性能差,易受温度和酸碱度影响这一难题,本实验采用食品添加剂β－环状糊精对其进行修饰。将β－环状糊精用高碘酸钠氧化成具有二醛结构的活性化合物,在一定条件下与超氧化物歧化酶（SOD）分子赖氨酸残基上的ε－NH2反应,经硼氢化钠还原,形成β－环状糊精修饰的SOD。测定结果表明,修饰后的SOD与不经修饰的SOD比较,在高热和酸碱状态下其稳定性能均有明显的提高。     

SOD 的稳定性及修饰的研究

为了获得活性较高且稳定性强的超氧化物歧化酶(superoxide dismutase,SOD),比较牛奶、木瓜、酵母菌3种不同来源的SOD,考察它们在不同p H值、温度、外源性试剂干扰条件下的稳定性。结论为牛奶中SOD的稳定性优于木瓜和酵母菌,牛奶中提取的SOD活性值为116 608 U/g。为使其更好的发挥作用,采用月桂酸对牛奶中SOD酶进行修饰,最终产品的酶活性值为115 127 U/g。     

葡聚糖接枝对大豆蛋白功能特性及结构的影响

采用干热糖基化对大豆分离蛋白进行改性,研究其功能特质及结构特性。以葡聚糖和大豆分离蛋白(soy protein isolate,SPI)为原料,考察底物质量比和反应时间两个因素。结果表明:蛋白质与糖质量比2∶1,反应温度60℃时,产物接枝比较高,褐变程度中等;与SPI相比,糖基化之后大豆蛋白的溶解度提高了72.72%,乳化活性(emulsifying activity,EAI)和乳化稳定性(emulsion stability,ESI)分别提高了117.53%和134.20%。十二烷基硫酸钠聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE)表明SPI与葡聚糖发生了糖基化反应;傅里叶红外光谱(Fourier transform infrared spectroscopy,FT-IR)和荧光光谱分析表明,糖链的引入导致了大豆蛋白空间结构的变化;模拟体外消化特性结果表明,葡聚糖糖基化修饰对SPI体外消化性的改善效果不明显。     

Impact of dextran conjugation on physicochemical and gelling properties of sweet potato protein through Maillard reaction

Covalently linked sweet potato protein (SPP)–dextran conjugates were produced through Maillard reaction, and the effects of this conjugation on physicochemical and gelling properties of SPP were studied. Formation of SPP–dextran-conjugated product was confirmed with increase in browning intensity and molecular weight, with concomitant reduction in free amino group content of the protein. Dry-heating period of 0, 1, 3, 5 and 7 days gave rise to 0%, 12.8%, 19.0%, 25.2% and 22.8% degree of conjugation (DC), respectively. High molecular weight protein polymer with polydispersed band above 50 kDa was formed. FTIR spectroscopic analysis showed that the C-O (amide I) and C-N (amide II) stretching bands were modified by the Maillard reaction. Conjugation of SPP with dextran reduced its denaturation temperature. SPP–dextran conjugate gels’ network structures were sustained by both physical interactions and covalent bonds. SPP–dextran conjugates’ gels had significantly improved hardness and resilience in comparison with the unmodified SPP (P < 0.05).     

Improvement of emulsifying properties of Maillard reaction products from β-conglycinin and dextran using controlled enzymatic hydrolysis

A novel emulsifier was prepared by conjugating soy β-conglycinin and dextran (MW 67 kDa) under dry-heated Maillard reaction followed by trypsin hydrolysis with the degree of hydrolysis (DH) at 2.2% and 6.5%. The emulsifying properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 2.2% and DH 6.5%) were investigated using zeta-potential, droplet size and creaming index of the emulsions. The results showed that hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) were capable of forming a fine emulsion (d₄₃ = 0.62 ± 0.04 μm, pH 7.0) which remained stable during 4 weeks of storage. A variety of physicochemical and interfacial properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates were investigated. Hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) had a much higher fraction of protein adsorption (F_ads) and a significantly lower saturation surface load (Γ_sat) compared with β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 6.5%). This might be due to its higher molecular flexibility, which benefited the adsorption and unfolding of peptide molecules at the droplet interface. These might explain its markedly improved emulsifying capability. The conjugation of β-conglycinin and dextran effectively enhanced the hydrophilicity of the oil droplets surfaces and improved the steric repulsion between the oil droplets. Therefore the emulsions were still stable after 4 weeks of storage against pH, ionic strength and thermal treatment. This study demonstrated that controlled enzymatic hydrolysis of protein–polysaccharide conjugates could be an effective method for preparing favourable emulsifiers.     

Characterization and improvement of rheological properties of sodium caseinate glycated with galactose, lactose and dextran

The aim of this work was to investigate the effect of non-enzymatic glycosylation with galactose, lactose, and 10 kDa dextran on the rheological properties of sodium caseinate. To promote the formation of covalent complexes, the reaction was done in solid state (a_w = 0.67), pH 7.0 (0.1 M sodium phosphate buffer), and temperature set at 50 and 60 °C. The progress of Maillard reaction was indirectly traced by measuring the formation of the Amadori compound, through furosine (2-furoylmethyl-lysine) analysis, and brown polymers, and the resulting glycoconjugates were characterized by LC/ESI-MS and SEC. Results showed a higher reactivity of galactose than lactose and dextran to form the glycoconjugates, due to its smaller molecular weight. Glycation with galactose and lactose increased the viscosity of caseinate and also altered its flow characteristics from Newtonian to shear-thinning. Oscillatory testing showed a higher elastic modulus (G′) in glycoconjugates when compared to non-glycated caseinate, especially with galactose, where a gel-like behaviour was observed after long incubation times. Glycation with dextran did not produce substantial improvements in the rheological properties of caseinate, probably due to the limited extent of the reaction. Our results show that by controlling the rate and extent of the Maillard reaction is a technologically feasible operation to improve the viscosity and gelling properties of sodium caseinate-based ingredients.     

聚唾液酸修饰CuZn-SOD及其形态和稳定性研究

聚唾液酸(Polysialic acid,PSA)因其更为有效的安全性,被公认为传统药用缓释材料——聚乙二醇(PEG)的理想替代材料。作者对蛋白质药物——铜锌超氧化物歧化酶(CuZn-SOD)的聚唾液酸修饰进行了初步研究。研究了修饰反应的主要条件:聚唾液酸经高碘酸钾氧化后生成的活化体,与超氧化物歧化酶以40∶1的摩尔比反应24h,可以达到理想修饰效果,生成的聚唾液酸修饰的超氧化物歧化酶衍生物(PSA-SOD)平均交联比达到了3.9±0.3。该衍生物经过SDS-PAGE电泳和原子力显微镜(AFM)检测测得其平均相对分子质量为90 000～100 000,分子粒径为10～15nm,约为天然超氧化物歧化酶的4倍。除此,PSA-SOD呈单颗粒包覆和多颗粒包覆两种显微形态。PSA-SOD进行稳定性试验表明,经聚唾液酸修饰的超氧化物歧化酶的酸碱稳定性、热稳定性和抗酶解稳定性都有了较大程度的提高。     

小麦胚芽蛋白糖基化反应改性的研究

以葡聚糖为糖基供体,采用糖基化反应对小麦胚芽蛋白进行改性。通过单因素实验摸索和正交实验优化确定了改性的最佳工艺条件:底物浓度2%,蛋白∶葡聚糖=1∶1,pH11,温度110℃,时间20min。在此条件下,接枝度达到11.27%,产物溶解性达到85.91%。反应产物在激发波长347nm,发射波长422nm处有最大荧光强度,且随着反应时间的延长,荧光强度增大,符合美拉德反应产物的荧光特征。傅立叶红外分析(FTIR)结果证实了葡聚糖以共价键的形式接入了小麦胚芽蛋白。      

Functional properties of milk proteins as affected by Maillard reaction induced oligomerisation

Milk proteins were modified by Maillard reaction with glucose, lactose, pectin and dextran and analysed for changes in molar mass distribution and functional properties. The study revealed that oligomeric (20,000–200,000 g/mol) and polymeric (>200,000 g/mol) Maillard reaction products with heterogeneous functional property profiles were generated. Compared to untreated milk proteins, milk protein/saccharide Maillard products formed highly viscous solutions and performed increased antioxidant capacity. Improved heat stability was detected for milk protein/dextran products, higher surface hydrophobicity for milk protein/glucose and milk protein/lactose products, and increased overrun for milk protein/pectin and milk protein/dextran products. Total milk protein/saccharide Maillard products formed outstandingly stable protein foams, Maillard products of total milk protein and glucose, lactose or pectin stable O/W-emulsions. Milk protein/pectin and milk protein/dextran Maillard products were characterized by increased emulsifying activity, and whey protein/saccharide products by enhanced pancreatic in vitro digestibility.The study characterizes Maillard reaction products of milk proteins and makes it possible to specifically select modified proteins for industrial applications according to the requirements towards food proteins, weighing changes in techno- and tropho-functional protein properties.     

葡聚糖修饰米根霉脂肪酶条件优化及其稳定性研究

采用经高碘酸钠活化的葡聚糖修饰米根霉脂肪酶,以获得具有较高酸解催化活性的脂肪酶。研究反应时间、反应pH值、还原剂浓度及葡聚糖质量分数对化学修饰效果的影响,并利用Box-Behnken设计法及响应面优化法对米根霉脂肪酶的化学修饰条件进行优化,当反应pH值为7.63、反应时间为15.53 h、还原剂浓度为0.20 mol/L、葡聚糖质量分数为0.3%时,脂肪酶酸解率可达到最高值37.28%。在40 ℃最适温度条件下,修饰酶的活性是原酶的2.2 倍,且经化学修饰后脂肪酶的稳定性有显著提高。