Effects of different oils on the properties of soy protein isolate emulsions and gels

The emulsion properties, protein adsorption and visco-elastic properties of heat-treated soy protein isolate (SPI) emulsions containing sunflower oil, soy oil and palm stearin were studied at neutral pH. The rheological properties, textural profile and fat adsorption capacity of subsequently induced glucono-δ-lactone (GDL) gels were investigated. At neutral pH the palm stearin emulsions showed higher stability than the sunflower and soy oil emulsions. The former also showed higher protein adsorption, emulsifying activity index and visco-elastic properties than the latter, indicating a higher denaturation degree for SPI at the oil/water interface of palm stearin emulsions at neutral pH. Acidified SPI-palm stearin emulsion gels were significantly harder than the soy and sunflower oil versions as well as the control (SPI without oil), whereas gels containing the two liquid oils were softer than the control. SPI-palm stearin gels also had higher fat adsorption capacity than SPI-sunflower oil/soy oil emulsion gels.     

Formation and properties of glycinin-rich and β-conglycinin-rich soy protein isolate gels induced by microbial transglutaminase

The gelation and gel properties of glycinin-rich and β-conglycinin-rich soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. At the same enzyme and protein substrate concentrations, the on-set of gelation of native SPI and the viscoelasticity development of correspondingly formed gels depended upon the relative ratio of glycinin to β-conglycinin. The turbidity analysis showed that the glycinin components also contributed to the increase in the turbidity of SPI solutions incubated with MTGase (at 37 °C). Textural profile analysis indicated that the glycinin components of SPIs principally contributed to the hardness, fracturability, gumminess and chewiness values of corresponding gels, while the cohesiveness and springness were mainly associated with the β-conglycinin components. The strength of MTGase-induced gels of various kinds of SPIs could be significantly improved by the thermal treatment. The protein solubility analyses of MTGase-induced gels, indicated that besides the covalent cross-links, hydrophobic and H-bondings and disulfide bonds were involved in the formation and maintenance of the glycinin-rich SPI gels, while in β-conglycinin-rich SPI case, the hydrophobic and H-bondings were the principal forces responsible for the maintenance of the gel structure. The results suggested that various kinds of SPI gels with different properties could be induced by MTGase, through controlling the glycinin to β-conglycinin ratio.     

微生物转谷氨酰胺酶对大豆分离蛋白乳液凝胶性能的影响

研究了不同油相比例（φ=0.2~0.6）的微生物φ转谷氨酰胺酶（MTGase）诱导的大豆分离蛋白（SPI）乳液凝胶性能及微观结构,发现提高乳液中的油相比例,凝胶的弹性模量G’及凝胶持水性均有显著提高并存在一定相关性,乳液凝胶形成的凝胶网络机械强度更大,油滴在酶促乳液凝胶中充当了良好的＂活性填充剂＂。     

菜豆属豆类蛋白酶促凝胶性能比较研究

研究比较芸豆(KPI)、红豆(RPI)和绿豆(MPI)3 种菜豆属类分离蛋白和大豆分离蛋白(SPI)在微生物转谷氨酰胺酶(MTGase)作用下的凝胶性能,并对其凝胶形成机理加以分析。SDS-PAGE 电泳和哈克流变分析结果表明：菜豆类分离蛋白是MTGase 的良好作用底物,初始成胶所需时间：KPI ＜ MPI ＜ SPI ＜ RPI。而酶反应后的凝胶G′值：RPI ＞ MPI ＞ KPI ＞ SPI,即KPI 形成凝胶最快,而RPI 最终成胶的强度最大;通过对不同溶剂下胶体溶解性的比较发现,除了酶共价交联外,静电相互作用,疏水作用及氢键都是形成凝胶的主要作用力,由于菜豆属类蛋白主要富含7S 球蛋白(不含二硫键),二硫键对其凝胶的稳定性作用不如SPI 明显。     

Physical properties of emulsion gels formulated with sonicated soy protein isolate

This study aimed to determine the effect of high-intensity ultrasound (HIU) on physical properties of soy protein isolate dispersions (SPI) and their addition to emulsion gels (EG) containing soybean oil (SBO), inulin (IN) and carrageenan (CAR). Sonicated and non-sonicated SPI dispersions were mixed with CAR, IN and SBO and heated at 90 °C for 30 min to gel the emulsion. An increase in solubility and oil binding capacity was observed in sonicated SPI dispersions (S-SPI) compared to the non-sonicated ones. HIU changed the molecular weight of SPI and decreased apparent viscosity in the dispersions. The use of S-SPI in the EG reduced the droplet size and increased the hardness and G′ values. The use of S-SPI allowed a reduction of 75% of carrageenan in the EG without affecting the hardness of the gel. The results suggest that HIU can be used to improve rheological properties of functional EG.     

花生蛋白-果胶复合乳液凝胶的流变学特性和微观结构

研究不同油相及其添加量对转谷氨酰胺酶诱导制备的花生蛋白-果胶复合乳液凝胶质地特性的影响规律,同时通过流变学和微观结构特性研究探索乳液凝胶的形成机理。结果表明：花生蛋白-果胶复合乳液凝胶的凝胶强度显著高于水凝胶。凝胶外观和储能模量（G’）结果表明油滴与蛋白-果胶组成的凝胶基质相互作用,从而影响乳液凝胶的质地和凝胶强度。油相添加量的增加可以使乳液凝胶的力学性能增强,网络结构更稳定。花生蛋白-果胶复合乳液凝胶的G’值和硬度随油相添加量的增加而增大,说明分散的油滴作为活性填料与凝胶基质相互作用。花生蛋白-果胶复合乳液凝胶的微观结构结果表明,油相添加量60%（V/V）时24度棕榈油为油相的乳液凝胶网络结构更致密。研究结果为花生蛋白-果胶复合乳液凝胶在食品领域的开发利用提供思路。     

Rheology and microstructure of myofibrillar protein-plant lipid composite gels: Effect of emulsion droplet size and membrane type

Composite gels were prepared from 2% myofibrillar protein (MP) with 10% imbedded pre-emulsified plant oils (olive and peanut) of various particle sizes at 0.6 M NaCl, pH 6.2. Dynamic rheological testing upon temperature sweeping (20-70 °C at 2 °C/min) showed substantial increases in G′ (elastic modulus) of MP sols/gels with the addition of emulsions, and the G′ increases were inversely related to the emulsion droplet size. Furthermore, gels containing emulsified olive oil had a greater (P < 0.05) hardness than those containing emulsified peanut oil. Regardless of oil types, MP-coated oil droplets exhibited stronger reinforcement of MP gels than Tween 80-stablized oil droplets; the latter composite gels had considerable syneresis. Light microscopy with paraffin sectioning revealed a stable gel structure when filled with protein-coated oil droplets, compared to gels with Tween 80-treated emulsions that showed coalesced oil droplets. These results suggest that rheological characteristics, hardness, texture, and water-holding capacity of MP gels were influenced by type of oils, the nature of the interfacial membrane, and the size of emulsion droplets.     

COAGULATION AND GELATION OF SOY PROTEIN ISOLATES INDUCED BY MICROBIAL TRANSGLUTAMINASE

The reaction process and corresponding mechanism of coagulation and gelation of native soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. The protein constituents of SPIs, including a majority of subunits of β‐conglycinin and acidic subunits of glycinin, could be polymerized by MTGase to form high weight molecular (WM) biopolymers. Both the coagulation and gelation reactions of native SPI solutions induced by MTGase were dependent upon the initial protein substrate concentration ([C] ₀ ). In the coagulating reactions, the turbidity of SPI solutions continually increased with increasing [C] ₀ in the range from 0.25 to 3.0%. As for the gelation reactions, with the concentration increasing from 3 to 8% (w/v), the onset time of gelation of native SPIs induced by 0.8 units/mL of MTGase at 37C shortened by ∼5‐fold, and the storage modulus (G′) of finally formed gels (after 4 h) increased from ∼1 to 1300 Pa. Both the coagulation and gelation reactions of SPI solutions were promoted remarkably by increasing the enzyme concentration. Sodium Dodecyl Sulfate‐Polyacrylamide Gel Electrophoresis analysis showed that the protein constituents of MTGase‐induced aggregates of SPI (2% w/v) were mainly composed of basic subunits of glycinin and some of newly cross‐linked high MW biopolymers. The solubility analysis of protein constituents indicated that the covalent cross‐linkage, hydrophobic and H bindings and disulfide bonds were mainly involved in the coagulation of SPI induced by MTGase.     

大豆分离蛋白对微生物转谷氨胺酶诱导鲢鱼糜凝胶形成的影响

本实验通过对鲢鱼糜凝胶特性和溶解率的测定及SDS-PAGE、扫描电镜观察,研究大豆分离蛋白(SPI)对微生物转谷氨酰胺酶(MTGase)诱导鱼糜凝胶形成的影响及作用机理。结果表明：SPI 和MTGase 均能显著提高鱼糜凝胶特性,但SPI 的添加会阻碍MTGase 对肌球蛋白重链(MHC)的交联,降低鱼糜凝胶特性,增加溶解率。SPI改善鲢鱼糜凝胶特性的机理是自身的凝胶作用和抑制蛋白酶活性。     

猪血浆蛋白乳化棕榈油对猪肉糜凝胶特性的影响

以质量分数25%和50%猪血浆蛋白乳化棕榈油替代猪背膘,研究其对猪肉糜凝胶特性、流变性、水分分布 状态和水分迁移特性的影响。结果表明：添加乳化棕榈油可显著提高猪肉糜凝胶的L*值、b*值、蒸煮得率、硬度 和弹性（P＜0.05）,在替代量为50%时猪肉糜凝胶有最高的L*值、b*值、蒸煮得率、硬度和弹性。在80 ℃,猪背 膘替代量为50%时猪肉糜的G’最高。低场核磁共振结果表明：添加乳化棕榈油猪肉糜凝胶的T22起始弛豫时间较短, T21的峰面积比例增加,而T22的峰面积比例降低,说明水分可移动性降低,不易流动的水分含量增加,猪肉糜凝胶 的保水性增强。     

Comparison of gelling properties and flow behaviors of microbial transglutaminase (MTGase) and pectin modified fish gelatin

The gelling and structural properties of microbial transglutaminase (MTGase) and pectin modified fish gelatin were compared to investigate their performances on altering fish gelatin properties. Our results showed that within a certain concentration, both MTGase and pectin had positive effects on the gelation point, melting point, gel strength, textural, and swelling properties of fish gelatin. Particularly, low pectin content (0.5%, w/v) could give fish gelatin gels the highest values of gel strength, melting temperature, and hardness. Meantime, flow behavior results showed that both MTGase and pectin could increase fish gelatin viscosity without changing its fluid characteristic, but the latter gave fish gelatin higher viscosity. Both MTGase and pectin could increase the lightness of fish gelatin gels but decreases its transparency. More importantly, fluorescence and UV absorbance spectra, particle size distribution, and confocal microscopy results indicated that MTGase and pectin could change the structure of fish gelatin with the formation of large aggregates. Compared with MTGae modified fish gelatin, pectin could endow fish gelatin had similar gel strength, thermal and textural properties to pig skin gelatin.     

Extra-Virgin Olive Oil and Cheap Vegetable Oils: Distinction and Detection of Adulteration as Determined by GC and Chemometrics

Refined oils including corn, sunflower, soybean, and palm oils as well as low-quality olive oil such as refined lampante and pomace olive oils are commonly used for extra-virgin olive oil (EVOO) adulteration. Indeed, K ₂₇₀ could be used as a parameter for the detection of EVOO fraud for each type of the studied refined oils, 10 % olive, 4 % pomace olive, 10 % palm, 5 % corn, and 2 % soybean oils. Moreover, the adulteration could also be detected by the increase of the trans fatty acid contents with 10 % pomace olive, 3 % soybean, 3 % sunflower, 2 % corn, and 10 % palm oils. Actually, stigmasta-3,5-diene content is one of the most effective means of detecting refined oils in EVOO at low levels: 2 % olive, 0.4 % pomace olive, 1 % palm, 0.2 % soybean, 0.5 % sunflower, and 0.1 % corn oils. Finally, the application of linear discriminant analysis could represent an alternative and innovative tool for faster and cheaper evaluation of EVOO adulteration.     

Evaluation of some physico-chemical properties of restructured trout and hake mince during cold gelation and chilled storage

Cold gelation was carried out on trout (Oncorhynchus mykiss) or on hake (Merluccius merluccius) mince with or without addition of fish oil and using microbial transglutaminase (MTGase). Products were stored at 4 °C for 6 days and lipid oxidation, protein oxidation, texture, water binding capacity, and colour were followed. Results indicated that MTGase was able to generate gels with good properties for both trout and hake. Gels prepared with trout were oxidised whilst gels prepared with hake were stable toward oxidation even in the presence of 5% fish oil. However, in the presence of oil, as an alternative for generating omega-3 enriched products, the activity of MTGase was impaired, as the gels took longer to reach maximum hardness. Furthermore, in all samples containing MTGase, protein oxidation was high.     

茶叶籽粕蛋白功能特性研究

以大豆分离蛋白为对照,研究碱法和酶法提取茶叶籽粕蛋白的功能特性。结果表明：酶法提取茶叶籽粕蛋白的溶解性、吸油性、乳化能力和乳化稳定性、起泡性、凝胶脆度优于碱法提取茶叶籽粕蛋白,而后者的吸水性、泡沫稳定性则优于前者,两者所形成蛋白凝胶的黏性和硬度相当。碱法和酶法提取的茶叶籽粕蛋白的乳化能力和乳化稳定性稍优于大豆分离蛋白,但起泡性和泡沫稳定性则不及大豆分离蛋白,溶解性与大豆分离蛋白相当,它们形成凝胶的最低质量分数分别为13%和15%,凝胶的黏性和硬度低于大豆分离蛋白。pH值、蛋白质量分数、NaCl浓度等因素对茶叶籽粕蛋白功能特性均有不同程度的影响。     

Improvement of microbial transglutaminase‐induced gelation of β‐conglycinin by conjugation with dextran

This work focused on the effect of glycosylation on the gelation ability of β‐conglycinin induced by microbial transglutaminase (MTGase). Rheological results indicated that the gels of β‐conglycinin‐dextran conjugate products exhibited higher G′ value (172.2 ± 8.6 Pa) compared with those of dry‐heated β‐conglycinin (75.2 ± 5.1 Pa), β‐conglycinin (53.3 ± 4.0 Pa) and β‐conglycinin‐dextran mixture (38.6 ± 2.6 Pa) after 4 h incubation with MTGase. The gels prepared from β‐conglycinin‐dextran conjugate products had higher hardness, fracturability, springiness and cohesiveness values determined by textural profile analysis. The turbidity of β‐conglycinin‐dextran conjugate products solution incubated with MTGase increased faster than those of the other three protein samples. The conjugated dextran in β‐conglycinin‐dextran conjugate products could inhibit extensive protein–protein interactions which might result in the formation of more ordered and stronger gel network structures during MTGase cross‐linking process. A compact and homogeneous gel networks in β‐conglycinin‐dextran conjugate products gels were also observed by scanning electron microscopy.     

Computed microtomography and mechanical property analysis of soy protein porous hydrogel prepared by homogenizing and microbial transglutaminase cross-linking

A novel, safe and rapid method for preparing soy protein-based porous hydrogel was described in this work. The porous hydrogel was synthesized by high speed homogenizing in the presence of microbial transglutaminase (MTGase) that catalyzed the cross-linking of the proteins. Computed microtomography (μCT) was used to characterize the porous structure of the formed gels. The extent of cross-linking and mechanical properties of the hydrogel were also evaluated. The influence of MTGase addition, homogenizing speed and soy protein isolates (SPI) dispersion pre-heating temperature on the porosity and mechanical properties of the hydrogel was investigated. The amount of MTGase, which determined the degree of cross-linking, gelation time and gel strength, played a critical role in preparation. With this method, soy protein porous hydrogel with controllable porous architecture was able to be prepared in a fast and simple way. This porous structure provided a special texture and some potential applications such as nutrients and flavors carrier for the hydrogel.     

甘草酸纤维茶树精油乳液凝胶的制备及其结构表征

选取茶树精油为风味油相,利用甘草酸自组装纳米纤维作为结构单元构建风味精油乳液凝胶体系,研究甘草酸纤维质量分数、茶树精油质量分数、油相组成对精油乳液凝胶外观、微观结构、流变学特性的影响。结果表明：利用甘草酸的两亲性和纤维化自组装,能成功制备出乳滴粒度小（2.5 μm）且具有蜂窝状网络微结构的茶树精油乳液凝胶;流变学测试显示该乳液凝胶具有高凝胶强度,较高质量分数的甘草酸纤维（4%）及油含量（40%）构建的乳液凝胶体系流变黏弹性更强、更稳定;在混合油相中,油相组成（添加葵花籽油或中链脂肪酸甘油三酯）的改变可以显著影响乳液凝胶粒度,最终改善风味乳液凝胶外观及结构特征。     

Evaluation of mungbean protein isolates at various levels as a substrate for microbial transglutaminase and water binding agent in pork myofibrillar protein gels

The objective of this study was to investigate the effect of mungbean protein isolate (MPI) on the potential possibility of water binding agent and as a substrate for the microbial transglutaminase (MTGase) in myofibrillar protein. Cooking loss (CL,%), gel strength (GS, gf), sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were measured. The addition of MPI reduced CL, indicating that it has a water binding capacity during cooking. The major protein band (53 kDa) of MPI appeared when MPI was mixed with MP, but it disappeared when MTGase was incorporated. MPI treatment changed the endothermic peaks as compared with those of CTL. MTGase (1%) mediated pork MP increased CL and GS (P < 0.05), and reduced peak temperatures with vanishing of endothermic intensity at 1st and 3rd peaks, suggesting the structural changes of protein gelation. In microstructures, MTGase treatment showed a finely stranded structure in MP gels, while MPI showed a conglomerated surface in MTGase‐mediated MP gels. These results indicated that MPI appears to be a water binding agent during cooking and function as a substrate for MTGase in MP gelation.     

谷氨酰胺转氨酶预交联改善CaSO4诱导大豆分离蛋白凝胶性的研究

酶法改性能够有效提升大豆蛋白的凝胶性。为了探讨谷氨酰胺转氨酶(transglutaminase, TGase)预交联对盐诱导大豆分离蛋白凝胶性的影响,通过控制酶浓度、预交联时间制备不同预交联程度的大豆分离蛋白(soy protein isolate,SPI)溶液,并研究其在CaSO₄作用下的成胶性能。结果显示,与未经TGase处理的SPI相比,TGase适度预交联能够显著提升SPI的凝胶品质。经3～5 U/g TGase预交联20 min或3 U/g TGase预交联20～30 min后,SPI凝胶性得到了不同程度的提升,其中弹性模量、屈服应力、屈服应变、持水率最大分别提高了124.5%、269.0%、135.0%及53.0%。然而,过度预交联产生过大的蛋白聚集体,导致最终形成的凝胶结构粗糙、多孔,凝胶强度、持水力等均显著下降(P<0.05)。由此可见,合理利用TGase对蛋白进行预交联处理能够改善SPI凝胶制品品质,对于TGase在食品工业中的应用及传统豆制品质构改良具有重要的指导意义。     

大豆分离蛋白对肌原纤维蛋白加热过程中结构及流变特性的影响

大豆分离蛋白（soybean protein isolate,SPI）作为优质的植物蛋白常被用于肉制品加工中,以提高产品产量和质地。研究添加SPI对肌原纤维蛋白（myofibrillar protein,MP）凝胶特性及MP加热过程中结构和流变特性的影响。结果表明：添加10%、20% SPI能提升混合凝胶的凝胶强度及保水性（P＜0.05）;加热过程中混合蛋白凝胶二级结构发生改变,但其变化规律尚不明确;添加SPI使混合凝胶储能模量及损耗模量下降;混合凝胶上清液十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱显示,肌球蛋白重链、肌动蛋白、SPI部分亚基均是参与凝胶形成的蛋白质。