转谷氨酰胺酶催化大豆蛋白和乳清蛋白合成耐热性聚合蛋白

用商品级转谷氨酰胺酶(TG-B)聚合大豆蛋白和乳清蛋白形成高耐热、耐酸的蛋白聚合物。蛋白聚合物的合成量由SDS-PAGE电泳结合凝胶成像分析测定;蛋白聚合物的耐热性用差示扫描量热法(DSC)测定;蛋白聚合物的酸溶解性用双缩脲法测定。结果表明TG-B聚合大豆蛋白和乳清蛋白形成的蛋白聚合物的最适条件为pH为6～7;反应温度30℃～45℃,反应时间4h,加酶量为6当量单位/g蛋白,在此条件下蛋白聚合物的转化量可达30%,所合成蛋白聚合物可耐130℃的热处理而不发生变性;并在pH3.2～4.3范围不发生沉淀。     

微生物转谷氨酰胺酶催化乳清蛋白聚合研究

采用SDS－PAGE分析，研究了不同条件下微生物转谷氨酰胺酶（MTGase）催化乳清蛋白（WPI）聚合。结果显示，MTGase可催化乳清蛋白的β－乳球蛋白（β-LG）和α－乳清蛋白（α－LA）聚合，形成低聚物或生物聚合物，其中β-LG更易受MTGase的催化，当TGase酶浓度一定时（0.5U/mL),TGase催化WPI聚合的最佳底物质量分数范围为2％－4％，对WPI进行加热预处理，同时添加还原剂，可明显提高MTGase对WPI的催化活性，MTGase催化WIP的最适PH值范围为6．5－7．5，当WPI经预热处理（85℃，15min），同时添加20mmol/L的DTT，TGase催化WPI聚合12h，可使质量分数为92％的β-LG和质量分数为75％的α－LA聚合。     

超滤浓缩乳清蛋白并分离乳糖的研究

采用管式超滤装置,选用切割分子量为20000的聚丙烯腈膜,对乳清进行了超滤浓缩试验。结果表明,降低乳清pH值可提高透液通量,把乳清调整至pH7．0,再离心除去不溶性钙盐,可获得最大透液透量。中性乳清经离心沉降后,在进口压力0.24MPa,温度45℃条件下浓缩180min,平均透液通量达到29．1kg／m2·h,蛋白质含量提高到2.85％,透过液中乳糖浓度变化不大。     

超滤分离大豆乳清蛋白的研究

就超滤分离大豆乳清蛋白的意义,分离工艺、膜与组件的评价、操作参数的影响与优选、膜清洗工艺及浓缩液的应用作了全面介绍和论述,为提高原料利用率,减轻乳清废液对城市环境的污染,提供了一条切实可行的新途径。     

转谷氨酰胺酶催化大豆蛋白和乳清蛋白合成耐热性聚合蛋白

用商品级转谷氨酰胺酶 (TG- B)聚合大豆蛋白和乳清蛋白形成高耐热、耐酸的蛋白聚合物。方法 :蛋白聚合物的合成量由 SDS- PAGE电泳结合凝胶成像分析测定 ;蛋白聚合物的耐热性用差示扫描量热法 (DSC)测定 ;蛋白聚合物的酸溶解性用双缩脲法测定。结果 :TG- B聚合大豆蛋白和乳清蛋白形成的蛋白聚合物的最适条件为 :p H为 6- 7;反应温度 30～ 45℃ ,反应时间 4h,加酶量为 6当量单位 / g蛋白 ,在此条件下蛋白聚合物的转化量可达 30 % ,所合成蛋白聚合物可耐 1 30℃的热处理而不发生变性 ;并在 p H3.2～ 4.3范围不发生沉淀。     

转谷氨酰胺酶催化大豆蛋白和乳清蛋白合成耐热性聚合蛋白

用商品级转谷氨酰胺酶 （TG- B）聚合大豆蛋白和乳清蛋白形成高耐热、耐酸的蛋白聚合物。方法 :蛋白聚合物的合成量由 SDS- PAGE电泳结合凝胶成像分析测定 ;蛋白聚合物的耐热性用差示扫描量热法 （DSC）测定 ;蛋白聚合物的酸溶解性用双缩脲法测定。结果 :TG- B聚合大豆蛋白和乳清蛋白形成的蛋白聚合物的最适条件为 :p H为 6- 7;反应温度 30～ 45℃ ,反应时间 4h,加酶量为 6当量单位 / g蛋白 ,在此条件下蛋白聚合物的转化量可达 30 % ,所合成蛋白聚合物可耐 1 30℃的热处理而不发生变性 ;并在 p H3.2～ 4.3范围不发生沉淀。      

超滤浓缩大豆乳清蛋白

本文对超滤技术在浓缩大豆乳清蛋白中的应用进行初步的探索,探索压力、温度、运行时间和浓缩倍率对浓缩大豆乳清蛋白的影响,结果表明截留率在92%以上。     

转谷氨酰胺酶催催化大豆蛋白和乳清蛋白合成耐热性聚合蛋白注

用商品级转谷氨酰胺酶（TG－B）聚合物大豆蛋白和乳清蛋白形成高耐热,耐酸的蛋白聚合物,蛋白聚合物的合成量由SDS－PAGE电泳结合 胶成像分析测定,蛋白聚合物的耐热性用差示扫描量热法（DSC）测定,蛋白聚合物的酸溶解性用双缩脲法测定,结果表明TG－B聚合大豆蛋白和乳清蛋白形成的蛋白聚合物的最适条件为：pH为6－7,反应温度30℃－45℃,反应时间4h,加酶量为6当量单位／g蛋白,在此条件下蛋白聚合的转化量可达305,所合成蛋白聚合物可耐130℃的热处理而不发生变性,并在pH3.2-4.3范围不发生沉淀。     

转谷氨酰胺酶聚合改性大豆分离蛋白的功能特性研究

研究了转谷氨酰胺酶(MTGase)聚合改性大豆分离蛋白的持水性、吸油性、溶解性、乳化性、发泡性及凝胶强度等功能特性。结果显示,与大豆分离蛋白相比,MTGase改性的大豆分离蛋白(MSPI)具有更高的凝胶性和乳化稳定性,但其溶解性、持水性、吸油性、起泡性与泡沫稳定性和乳化性明显减弱。     

Transglutaminase cross-linking to enhance elastic properties of soy protein hydrogels with intercalated montmorillonite nanoclay

To strengthen the network of bio-nanocomposite hydrogels, layered montmorillonite (MMT) nanoclay was intercalated by surface-coating with soy protein (SP) before mixing with 6% w/v SP for cross-linking by microbial transglutaminase (mTGase). Dynamic rheology was performed to study variables of NaCl and mTGase concentrations, with and without 1% w/v MMT. Without mTGase, the highest storage modulus (G′) was observed at 100 mM for samples without MMT, which was twice of the highest G′ for samples with MMT, at 200 mM NaCl. With mTGase, a shorter gelation time and a stronger hydrogel were observed at a higher enzyme level. Overall, the non-gelling 6% w/v SP dispersion was transformed to a hydrogel with G′ of 1099 Pa after addition of 100 mM NaCl and 1% SP-coated MMT and treatments by 6.25 U/g-protein mTGase for 2 h and heating/cooling steps. The integration of surface-coating and mTGase cross-linking is promising to improve properties of the nanocomposite system.     

乳清蛋白酶改性综述

乳清蛋白的酶法改性主要包括水解和交联。其中，用转谷氨酰胺酶改性具有比较大的发展潜力。     

Nanostructure development during peroxidase catalysed cross-linking of α-lactalbumin

Whereas extensive work has been done on the food functional and chemical aspects of enzymatic protein cross-linking, relatively little is known about the nanostructure and physical-chemical properties of enzymatically cross-linked protein. We investigate how nanostructure develops during enzymatic cross-linking of the 4 tyrosine residues of the globular protein apo α-lactalbumin. Protein cross-linking is catalysed by Horseradish Peroxidase, under the periodic addition of peroxide. We use on-line static and dynamic light scattering, combined with on-line UV-spectroscopy to simultaneously probe the development of nanostructure, the extent of dityrosine formation, and the catalytic state of the enzyme, as a function of the number of peroxide additions. It is found that initially, the rate of dityrosine formation is high, whereas the increase in the solution size of the cross-linked protein is limited. At later stages, the increase in solution size is significant whereas dityrosine formation slows down. Finally, the reaction stops due to enzyme inactivation. Off-line size exclusion chromatography shows that the initial phase corresponds to a fast cross-linking of monomers into small oligomers, followed by a slower joining of oligomers into large protein polymers. Consistent with this, Atomic Force Microscopy shows very heterogeneous polymers, apparently consisting of subunits that we identify with the oligomers formed in the first phase of the reaction. The dependence of the solution size on the molar mass of the cross-linked protein is determined using static and dynamic light scattering on fractionated reaction products. For sizes ranging from 30 nm to 80 nm, the protein polymers consist of 100–1000 α-lactalbumin subunits, and have molar masses of 10⁶–10⁷ g/mol. Apparent internal protein densities of the protein polymers calculated from these numbers are only a few weight percent, indicating a very dilute, open architecture of the cross-linked protein.     

乳清蛋白酶改性综述

乳清蛋白通过改性 ,可以加强其功能性质 ,从而合理利用资源 ,开发新产品 ,扩大在食品中的应用。乳清蛋白的改性方法有化学改性、物理改性和酶改性。酶改性主要包括水解和交联。其中 ,用转谷氨酰胺酶改性具有比较大的发展潜力。     

Modifications of soy protein isolates using combined extrusion pre-treatment and controlled enzymatic hydrolysis for improved emulsifying properties

Effects of combined extrusion pre-treatment and controlled enzymatic hydrolysis on the physico-chemical properties and emulsifying properties of soy protein isolates (SPI) have been investigated. Results showed that extrusion pre-treatment caused a marked improvement in the accessibility of SPI to enzymatic hydrolysis, resulting in changes in degree of hydrolysis (DH), protein solubility (PS), surface hydrophobicity (H₀) and molecular weight distributions (MWD) for ESPIH (extrusion pre-treated SPI hydrolysates). It was observed that emulsion systems formed by control SPI or SPIH (SPI hydrolysates) (20% v/v oil, 1.6% w/v emulsifier, and pH 7.0) were unstable over a quiescent storage period of 21 days, due to bridging flocculation and creaming. However, ESPIH (9.1% DH) was capable of producing a very fine emulsion (d₃₂ = 0.42 μm, d₄₃ = 2.01 μm) which remained stable over a long term quiescent storage. Various surface properties of ESPIH products have also been studied in relation to DH and emulsifying functionalities. It was suggested that significantly increased protein solubility and decreased molecular weight could be the main reasons for the greatly improved emulsifying capability of ESPIH. This study demonstrated that modified soy protein could be an excellent emulsifying agent for food and other applications. It also demonstrated that combined extrusion pre-treatment and enzymatic hydrolysis could be a highly effective method for functionality modification of globular proteins.     

Characteristics of edible films made from dairy proteins and zein hydrolysate cross-linked with transglutaminase

The main objectives of this research were to develop whey protein or casein films incorporating zein hydrolysate and also cross‐linked by transglutaminase as to well as characterize the physical and mechanical properties of the film. Zein hydrolysate decreased the solubility of the whey protein film (P < 0.05), while treatment with transglutaminase did not change the solubility of the film significantly. Electrophoresis patterns demonstrated that casein molecules were cross‐linked by transglutaminase and the extent of this cross‐linkage was further increased when zein hydrolysate was added. In addition, the use of zein hydrolysate decreased the tensile strength of the whey protein film by 35–45%. The elongation of the casein film was increased by 41% because of the action of transglutaminase and zein hydrolysate (P < 0.05). The water vapour permeability of the films was not significantly different. As the addition of zein hydrolysate and treatment with transglutaminase improved the flexibility of the films, the level of plasticizer required to maintain film flexibility could be reduced without sacrificing their water vapour permeability.     

The impact of transglutaminase on soy proteins and tofu texture

The enzyme transglutaminase was investigated for its cross-linking effect on the soy proteins of tofu. In vitro incubations confirmed that soy proteins are excellent substrates for transglutaminase, especially when denatured. The macroscopic effects resulting from the addition of transglutaminase were compared to changes at the microstructural and molecular level. Treatment produced a firmer tofu, with a significantly increased fracture force. Examination by SEM showed a change in the matrix structure, with transglutaminase resulting in a finer-stranded, uniform network that accounted for the increase in fracture force. At the molecular level, little, if any, cross-linking occurred within the tofu matrix in situ. This suggests that the change in functional properties afforded by addition of transglutaminase to tofu is due to a side reaction of the enzyme, for example hydrolysis of glutamine residues, rather than its cross-linking activity. These ideas are further explored in the accompanying paper.     

Enhancing the adsorption of the proteins in the soy whey wastewater using foam separation column fitted with internal baffles

In order to promote industrialization of protein recovery from soy whey wastewater using foam separation, a novel foam separation column fitted with baffles consisting of circular disk segments placed at regular intervals in the liquid layer of the column (known as CIB in this paper) was developed to intensify the interfacial adsorption of the proteins. The column was evaluated by studying the effects of: 1. volumetric air flow rate, 2. the initial concentration of the proteins in the soy whey water, 3. the size and spacing of the disk segments on protein adsorption characteristics. The results showed that such a column could significantly intensify the adsorption of proteins. The maximum surface excess was obtained at a volumetric air flow rate of 250 mL/min, a baffle spacing of 10 mm and a disk segment chord length of 29.8 mm. At an initial concentration of the proteins of 1.8 g/L, the surface excess given by the baffled foam column was 193% higher than that given by an unbaffled column.     

Production of soy protein isolates with low phytic acid content by membrane technologies: Impact of the extraction and ultrafiltration/diafiltration conditions

The content of the antinutrient, phytic acid, of soy protein was analyzed during their extraction and purification by a series of ultrafiltration and diafiltration steps. The phosphorus content of the extracts was used as an indication of their phytic acid content and their ash content as an indication of their mineral content. The extraction of soy proteins was conducted by using a 2³ factorial experimental design, pH (7.5 or 9), solvent (0.06 M KCl or water), and temperature (25 °C or 50 °C). The most promising extraction conditions were 0.06 M KCl/pH 9.0/25 °C for the lowest phosphorus to protein ratio (12.2 ± 0.1 mg P/g protein) and H₂O/pH 9.0/50 °C for the combination of low phosphorus to protein ratio and the lowest ash content (13.9 ± 1.2 mg P/g protein, 9.6 ± 0.8% w/w ash content). After extraction, soy proteins were purified by sequential ultrafiltration (UF) with a volume concentration ratio (VCR) of 5 and diafiltration (DF) with volume diafiltration ratio (VD) of 4. Extracts were purified with no pH adjustment or with pH adjustment to 6.5 between the UF and the DF steps. The extraction conditions 0.06 M KCl/pH 9.0/25 °C and the purification conditions UF pH 9.0/DF pH 6.5 showed the lowest phosphorus to protein ratio (4.4 ± 0.3 mg P/g protein) and reduced membrane fouling when compared to extraction conditions with water.