Study on the Functional Properties of Soybean Protein Isolate Cross-Linked with Gelatin by Microbial Transglutaminase

A microbial transglutaminase was used to cross-link soybean protein isolates in the presence of gelatin to prepare a cross-linked composite soybean protein-gelatin. Cross-linking conditions, such as total proteins, the ratio of soybean protein isolates to gelatin, and original pH, were fixed at 5% (w/v), 4:1 (w/w), and 7.5, respectively. The 4-hydroxyproline content in the modified product was measured and used as an index to select suitable transglutaminase addition, reaction temperature, and time by single factor experiments, which were found to be 20 U/g proteins, 40°C, and 2 h, respectively. Under the identified conditions, a modified product with 4-hydroxyproline content of about 36 mg/g proteins was prepared, and its functional properties were evaluated. SDS-PAGE analysis showed that several protein polymers existed in the modified product. Compared to the original soybean protein isolates or a cross-linked soybean protein isolates, the modified product had a better emulsifying stability and water holding capacity but a poor enzymatic digestibility in vitro, emulsifying activity and oil binding capacity; meanwhile, the dispersions formed by the modified product exhibited the highest apparent viscosity, storage modulus, and viscous modulus.     

微生物转谷氨酰胺酶催化酪蛋白酸钠聚合物的功能特性研究

研究了微生物转谷氨酰胺酶(TGase)催化酪蛋白酸钠聚合对其功能特性的影响。结果显示,随着催化时间的增加,其各组份含量不断减少,同时生成的聚合物含量不断增加,比较了TGase催化不同酪蛋白的聚合速率,结果显示转谷氨酰胺酶较易催化α-和β-酪蛋白,而不易催化κ-酪蛋白TGase催化聚合酪蛋白酸钠能明显改善其乳化性能,聚合时间越长,乳化指数越高,而乳化稳定性随聚合时间先升后降,4h时最高TGase催化酪蛋白酸钠还可提高其热稳定性,然而对其起泡性影响不大     

转谷氨酰胺酶对蛋白质凝胶性能的影响

本文研究了转谷氨酰胺酶浓度、反应温度、pH、时间对非肉蛋白质凝胶硬度的影响。结果表明转谷氨酰胺酶添加浓度在10-40U／g蛋白质，反应温度4-60℃，pH6-7，反应时间50-300min范围内，对于大豆分离蛋白、酪蛋白、乳清浓缩蛋白、卵清蛋白、明胶蛋白5种非肉蛋白质作用，均可以获得蛋白质凝胶能力以及凝胶性能的提高，表现在形成凝胶蛋白质极限浓度的降低以及凝胶硬度的提高。     

Study of Some Functional Properties of Casein: Effect of pH and Tryptic Hydrolysis

The trypsin was used to hydrolyze commercial casein at varied times and pH range. The functional properties studied were the emulsifying capacity (EC), the emulsifying activity index (EAI), and the emulsion stability (ES). The dispersed phase used was corn oil. The tryptic hydrolysis was beneficial to the solubility and EC of casein in practically all pH values and reaction times. In case of EAI, this same effect was less intense and was observed only in acid region (pH 3.0 to 5.0), while for ES the trypsin action was mainly deleterious in almost all pH range and reaction times.     

Casein gelation under simultaneous action of transglutaminase and glucono‐δ‐lactone

Casein solutions (5% w/v) were treated with microbial transglutaminase (MTG) and glucono‐δ‐lactone (GDL) under varying conditions in order to obtain gels. Storage modulus (G ′) and gelation time of the gels were measured by oscillation rheometry, while protein cross‐linking was determined by gel permeation chromatography. The addition of only GDL to milk resulted in very weak gels, while MTG on its own was not able to create gel networks. Simultaneous action of both ingredients led to gels, the firmness of which was linearly related to the added amount of MTG, but passed through a maximum with rising GDL concentrations. Using chromatographical analysis, increasing G ′ values were interrelated with the formation of MTG‐induced oligomers. The gelation time was directly proportional to the GDL concentration but not influenced by the addition of MTG within the studied range of concentration.     

Effect of Dietary Fiber Constituents on the In Vitro Digestibility of Casein

The in vitro digestibility of casein was substantially decreased by food type gums in the following order: karaya > ghatti > tragacanth > guar > locust bean. Extent of reduction of protein digestibility appeared to be related to the structure of the gum (degree of branching and extent of ionization). The fiber constituents, holocellulose, lignin, apple pectin, and the residues from protease predigested wheat bran and great northern bean, when present, significantly (P < 0.05) reduced casein digestibility. Gel filtration of the soluble portion from the casein hydrolysates containing pectin and bran or bean residues showed the presence of peptide fractions of larger molecular weight than those in a hydrolysate from the casein control. Results supported the hypothesis that dietary fiber constituents may reduce protein digestibility and increase nitrogen excretion through ionic interaction, matrix restriction, and modification of filtration characteristics by the fiber components tested.     

Casein hydration and fat emulsification during manufacture of imitation cheese, and effects of emulsifying salts reduction

The manufacture of imitation cheese in a Farinograph was interrupted at various times, and the casein matrix formed and the free liquid were collected and analysed. During manufacture, a torque profile was generated, which showed three distinctive stages; an initial torque peak “peak-1”, followed by a trough and finally a second “peak-2”. Analyses provided quantitative and qualitative evidence that the initial manufacturing stage (peak-1) was concerned with water uptake and the formation of a hydrated casein matrix, as ∼75% of the added water was absorbed. This was followed by a fat emulsification phase (trough) and, once sufficiently emulsified, by the incorporation of the fat to form a homogeneous cheese mass, at peak-2. A similar approach showed that the effect of emulsifying salts reduction was to retard casein hydration, reflected in an increase in peak-1 torque, and led to a prolonged mixing time to sufficiently emulsify fat and allow its incorporation.     

Gelation and In Vitro Digestibility of Soybean Protein Isolate Treated by a Ternary System Containing Horseradish Peroxidase,Glucose Oxidase,and Glucose

The aim of the present study was to investigate the potential application of a ternary system containing horseradish peroxidase, glucose oxidase, and glucose for the oxidative cross-linking of soybean protein isolate. Protein content, reaction temperature, and original pH were fixed at 30 g/L, 37°C, and 7.0, while suitable glucose, glucose oxidase, horseradish peroxidase addition, and reaction time selected from single factor trials for the one-step treatment were 0.1 mmol, 4.0 U, 200 U/g protein, and 3 h, respectively. In the two-step treatment, glucose, glucose oxidase, and horseradish peroxidase addition were the same, but a reaction time of 1 or 2 h was used for the glucose oxidase or horseradish peroxidase treatment. Two modified soybean protein isolates obtained by the one- and two-step treatment contained some protein polymers, had relative dityrosine content of 414 and 381, respectively, and showed lower in vitro digestibility and less free sulfhydryl than the control soybean protein isolate. During acidification induced by glucono-δ-lactone, the modified soybean protein isolates showed shorter gelation time (57 and 61 versus 72 min), lower loss tangent and gelation point temperature (52.9 and 53.2 versus 62.7°C) but higher final storage modulus than the control soybean protein isolate. The acidified gels prepared from the modified soybean protein isolates also exhibited enhanced hardness, springiness, cohesiveness, and chewiness, and finer microstructural features. The ternary system was capable of treating protein ingredients to improve their gelation properties.     

谷氨酰胺转氨酶在CO2超临界流体介质与水相介质中对胶原交联作用对比

探讨了CO2超临界流体(SFC-CO2)介质中谷氨酰胺转氨酶(TGase)对胶原的交联作用,且采用差示扫描量热法(DSC)表征胶原交联效果,并与常规水相介质条件下的酶催化胶原交联反应作出对比分析。结果表明:在SCF-CO2介质中TGase催化胶原的交联反应是能发生的,酶处理后胶原的热稳定性得到了显著的提高,且与水相介质条件下酶处理的胶原相比,其热变性温度提高了10～20℃。本试验得出TGase在SCF-CO2介质中催化胶原交联反应较适宜的条件为:时间2 h、温度40℃、酶用量40～60 U/g、pH值6.0～7.0、压力8.0 MPa。     

Relationship between In Vitro Digestibility of Casein and its Content of Lysinoalanine and D-Amino Acids

Alkali and heat induce changes in proteins. These include racemization of L- to D-amino acids and crosslinking via lysinoalanine. Since high-quality proteins are presumably well-digested, possible effects of D-amino acid and lysinoalanine contents on food casein digestibility was examined. The following variables, which were expected to influence all three parameters, were evaluated: (a) pH (8-14); (b) temperature (25-75°C); and (c) time of treatment (10 min to 24 hr). An approximately inverse relationship was observed between D-ammo acid and lysinoalanine content and the extent of proteolysis. Such changes may lower the quality and safety of foods.     

转谷氨酰胺酶对鲤鱼肌原纤维蛋白乳化活性和凝胶特性的影响

目的:研究添加转谷氨酰胺酶(Transglutaminase,TG)对鲤鱼肌原纤维蛋白乳化活性和凝胶特性的影响,为改善鱼糜制品的品质特性提供理论依据。方法:肌原纤维蛋白溶液浓度为40 mg/mL,TG添加量为蛋白溶液的0%、0.1%、0.2%、0.3%、0.4%(W/V),测定蛋白溶液的乳化活性及凝胶特性指标。结果:随着TG添加量的增加肌原纤维蛋白溶液乳化活性降低(p<0.05);TG添加增大了蛋白浊度(p<0.05);蛋白流变结果表明,随着TG添加量的增加显著增大储能模量(G')(p<0.05),降低起始凝胶温度,并提高蛋白变性温度;与对照相比,添加0.1%的TG会降低凝胶持水性,但是进一步增加TG对凝胶持水性影响不显著(p>0.05);添加TG显著降低了凝胶白度(p<0.05);凝胶质构测定结果显示,随着TG添加量的增加,会改进蛋白质的凝胶特性,显著增加凝胶弹性和硬度(p<0.05)。结论:肌原纤维蛋白中添加TG到能够降低蛋白的乳化特性,但会改进肌原纤维蛋白的凝胶特性。     

培养基组成对轮枝链霉菌合成谷氨酰胺转胺酶的影响

对产谷氨酰胺转胺酶菌种轮枝链霉菌（Streptoverticillium）SK-1的摇瓶条件进行了研究,结果表明当起始pH值为6.5～8.0,氮源、碳源为蛋白胨与甘油,培养时间为110h时,酶活最高可达1.8μmol/(min     

Determination of D-Amino Acids in Some Processed Foods and Effect of Racemization on In Vitro Digestibility of Casein

Several processed foods and controls were analyzed by gas chromatography for the presence of D-amino acids. The concentration of each of the D-amino acids detected in the processed foods was approximately the same as that in the controls except that D-aspartic acid was significantly higher in dark toast surface and extruded soy flour. In vitro digestibility of casein which was alkali-treated to cause racemization, but without lysinoalanine (LAL) formation, was essentially the same as that of racemized casein containing LAL, but was lower than that of nonracemized control casein.     

赖氨酸与谷氨酰胺在谷氨酰胺转胺酶作用下的交联反应

本文研究了赖氨酸与谷氨酰胺在谷氨酰胺转胺酶催化下的交联反应。探讨了底物比、加酶量、pH值、反应温度和反应时间对聚合度的影响。利用Design-Expert6.0.3软件优化得出交联反应的最佳工艺条件为底物比2.15、加酶量14.39U/g、pH值8.0、温度42℃和反应时间94min。同时,分析了各因素之间的交互效应。     

In Vitro Angiotensin I-Converting Enzyme Inhibition of Casein Hydrolysate Responsible for Plastein Reaction in Ethanol-Water Medium,Solvent Fractionation,and Protease Digestion

A casein hydrolysate generated by Alcalase had in vitro ACE-inhibitory activity of 44.4%, and was treated by Alcalase-catalyzed plastein reaction in ethanol-water medium. Alcalase addition, ethanol, substrate concentration, and reaction temperature optimized from experimental design were 8.36 kU/g peptides, 56.8 (v/v), 56.8% (w/v), and 37.5°C, respectively, when reaction time was fixed at 6 h. Two treated casein hydrolysates, namely TCH4 and TCH8, were obtained with reaction time of 4 and 8 h, and exhibited the highest ACE-inhibitory activity of 62.5% or the greatest reaction extent but an activity of 35.6%, respectively. Fractionation of TCH4 and TCH8 by applying ethanol-water of 7:3 (v/v) conferred the obtained supernatant (precipitate) fractionates higher (lower) activity than the parent substrate, while applying ethanol-water of 3:7 (v/v) or water led to an opposite result in activity for the fractionates. In vitro digestion of TCH4, TCH8, and their fractionates revealed that they had resistance in activity towards the investigated four proteases, as the resulted 47 out of 48 digests had higher activities than casein hydrolysate. TCH8 exhibited better protease resistance than TCH4. It is concluded that the applied plastein reaction can enhance ACE inhibition and protease resistance of casein hydrolysate.     

Ace Inhibition and Enzymatic Resistance In Vitro of a Casein Hydrolysate Subjected to Plastein Reaction in the Presence of Extrinsic Proline and Ethanol- or Methanol-Water Fractionation

Casein was hydrolyzed by alcalase to a degree of hydrolysis of 10.9% to obtain a hydrolysate having ACE-inhibition in vitro with an IC₅₀ value of 52.6 μg/mL. The prepared hydrolysate was modified by alcalase-catalyzed plastein reaction with extrinsic proline added at 0.4 mol/mol free amino groups (on the basis of the hydrolysate), and fractionated by ethanol- or methanol-water solvents in proportions of 3:7, 5:5, or 7:3 (v/v), respectively. With the decrease of free amino groups of the modified hydrolysate as the response, the optimized plastein reaction conditions were alcalase addition of 3.1 kU/g peptides, substrate concentration of 50% (w/v), and reaction temperature of 25°C. Four modified hydrolysates prepared with different reaction times exhibited higher ACE-inhibitory activities than the original hydrolysate. The evaluation results showed that solvent fractionation of the modified hydrolysate with the maximum activity (IC₅₀ = 13.0 μg/mL) yielded the separated soluble fraction's higher activity but the precipitate fraction's lower one. Further enzymatic digestion of the modified hydrolysate with the maximum activity and its two fractionated products by four proteases in vitro caused damage to the activities, but the residual activities of the final digests were higher than that of the original hydrolysate, indicating that the plastein reaction could confer casein hydrolysate protease resistance.     

磷脂酶修饰提高蛋黄磷脂乳化性及稳定性的研究

鸡蛋蛋黄在食品加工中经高温处理乳化性会显著下降,用磷脂酶修饰蛋黄磷脂,将其转变为溶血磷脂,使改性后的蛋黄在高温、低pH、高离子浓度环境下仍具有良好的乳化性及稳定性.本试验研究了磷脂酶修饰后蛋黄粉的乳化性和热稳定性.结果表明:改性蛋黄粉的乳化性、热稳定性都有显著提高.与普通蛋黄粉相比,改性蛋黄粉具有较强的抗酸、抗碱能力,乳化性提高了30%,且乳化稳定性是普通蛋黄粉的4倍.通过差示扫描量热仪(DSC)分析可知,改性蛋黄的变性温度高达95℃,显示出很强的耐热性.     

蛋白乳化活性与分子结构的关系

本文从蛋白分子二硫键以及非共价作用两方面综述了蛋白分子的柔韧性与蛋白乳化活性的关系。讨论了设计新的蛋白乳化剂的研究方向     

水热磷酸化改性大豆浓缩蛋白乳化性质的研究

采用水热磷酸化处理修饰大豆浓缩蛋白(Soybean Protein Concentrate,SPC),主要研究在SPC中添加不同浓度的三聚磷酸钠(SodiumTripolyphosphate,STTP)经水热处理改性后,SPC的磷酸化程度、乳化性质的变化。通过水热处理过程中向SPC添加0.1%~3%的STTP制备出不同磷酸化程度的磷酸化改性大豆浓缩蛋白(简称0.1%~3%P-HSPC);同时研究了改性前后SPC乳液乳析率、粒度分布的变化。结果表明:其中添加0.3%、0.5%、0.7%的STTP所得改性蛋白的磷酸化程度分别为0.226%、0.253%、0.28%,其磷酸化程度高于其他STTP浓度制得的改性磷酸化蛋白;并且改性后的SPC乳化性质有明显改善。     

喷射蒸煮处理对米糠蛋白功能特性及体外消化性的影响

研究了喷射蒸煮(HTC)处理对天然米糠蛋白(RBP)与热稳定米糠蛋白(HRBP)提取的影响,并对蛋白的粒度、亚基组成、接枝度、功能性及体外消化性能进行表征。研究表明:HTC处理能显著提高RBP与HRBP的得率(分别从44.9%与14.8%增加到52.2%与44.5%),但对蛋白的纯度没有显著影响。HTC处理后RBP与HRBP的粒度分别从73.6 nm与149.1 nm降低到46.8 nm与96.6 nm,同时生成接枝度28.0%与9.4%的糖基化产物。SDS-PAGE电泳图谱表明,处理后的米糠蛋白生成高分子质量的蛋白聚集体与糖基化产物。HTC处理更有利于HRBP功能性与消化性的提高,且HRBP具有RBP类似的溶解度曲线、起泡能力、泡沫稳定性与良好的乳化能力与消化能力,尽管该处理降低了天然米糠蛋白的消化性。