GELLING AND COLOR PROPERTIES OF OSTRICH (STRUTHIO CAMELUS) EGG WHITE

The effect of temperature upon the denaturation process of ostrich egg‐white protein was studied, and it compared with that of commercial hen eggs. Turbidity and color properties evolution were used to determine this effect. In addition, egg‐white gels (from both ostrich and hen egg whites) were obtained by heat treatment at 80C, and these were characterized by means of color, textural properties and water‐holding capacity (WHC). Results showed that although 55C was the temperature for the start of coagulation in both types of egg white, only in hen egg white was the process completed at 65C. The gels obtained at 80C (both ostrich and hen egg‐white gels) presented a strong structure that would allow ostrich egg white to be used as a gelling agent in the food industry as it happens with hen egg white.     

L-组氨酸修饰乳清蛋白结构及其热诱导凝胶特性

采用L-组氨酸（L-His）作为蛋白凝胶功能性的增强剂,将其加入乳清分离蛋白溶液中制备热诱导凝胶,研究L-His对乳清蛋白结构及其凝胶特性的影响。结果表明：在乳清蛋白等电点（pI 5.2）时蛋白形成尺度约1 700 nm、具有极小比表面积且几乎不带电的蛋白聚集体,远离蛋白等电点时则所形成的聚集体大小约为400 nm;L-His抑制蛋白聚集体的形成而减小粒径、显著提高聚集体比表面积,促进蛋白分子结构展开并提高其带电量。在经历热诱导后,乳清蛋白在其等电点时形成持水性差的白色凝胶,而在其他pH值时则形成持水性高的黄色凝胶且越远离等电点,胶体黄度值越大;L-His的加入对凝胶颜色变化无显著影响,但能够显著提高凝胶的持水性（P＜0.05）;有效提高凝胶的质地特性,特别是在pH 7.59和pH 9.74时显著提高乳清蛋白凝胶的弹性及咀嚼性（P＜0.05）。这些质构变化可能主要归结于L-His改变了凝胶内的氢键、二硫键和疏水作用力的重排。总之,L-His修饰乳清蛋白结构而改变其凝胶性能且同时受到pH值的影响。     

提取条件对鲨鱼肉盐溶蛋白热诱导凝胶特性的影响

以鲨鱼肉为材料,研究NaCl 浓度、pH 值、静置提取时间及加热时间对鱼肉盐溶蛋白热诱导凝胶保水性和质构特性的影响。结果表明：鲨鱼肉盐溶蛋白凝胶的保水性、硬度、弹性和黏聚性与NaCl 溶液浓度呈正相关;在NaCl 溶液浓度0.8mol/L、pH6.5～7.0、静置提取时间24h、40℃加热40～60min 时形成的凝胶保水性及其质构指标较理想;40℃加热盐溶蛋白,有利于形成凝胶结构,但随着加热时间的延长,盐溶蛋白凝胶硬度增加,保水性降低。     

植物模拟蛋液体系构建及凝胶性质研究

本文以绿豆蛋白、甲基纤维素、κ-卡拉胶（κ-carrageenan,KC）和高酰基结冷胶（high acyl gellan gum,HA）等成分为原料,构建了以绿豆蛋白为基体的模拟蛋液体系。通过测定质构、动态流变、持水性和微观结构等指标,考察了主要凝胶剂KC和HA配比对模拟蛋液凝胶质构性质、流变性质、持水性和微观结构等的影响。质构分析和持水性测定结果表明,KC是模拟蛋液凝胶强度和硬度的决定性因素,而HA可提高凝胶的弹性、内聚性、咀嚼性和持水性。温度扫描结果显示模拟蛋液和天然蛋液在加热和冷却过程中储能模量（G′）始终大于损耗模量（G″）,说明两者体系均以弹性为主体。随着HA质量比的提高,复合溶胶的黏度、储能模量（G′）和损耗模量（G″）增加,表明HA可改善模拟蛋液溶胶的黏性性质。扫描电镜结果显示,KC和HA可形成独立的互穿聚合物网络,具有一定的相容性和交联性。感官评定结果可知,当KC/HA配比为1.2:0.4时植物模拟煎蛋综合感官评分最高,和天然煎蛋在口感、组织结构和风味等方面最相近。综上所述,通过研究模拟蛋液体系中不同比例KC/HA的力学性能及相互作用机理,为植物基蛋类模拟制品的开发利用提供理论依据。     

Comparative assessment of textural properties and microstructure of composite gels prepared from gelatine or gellan with maize starch and/or egg white

Single component gels (SCG) were formed from gelatine, gellan, maize starch or egg white, while binary composite gel (BCG) and ternary composite gel (TCG) were formed by mixing gelatine or gellan with maize starch and/or egg white. Each type of SCG exhibited distinct textural and microstructure characteristics. Gelatine‐SCG was the softest to hold but has the strongest and the most elastic network compared with other SCG. The effects of gelatine or gellan proportions on the textural properties of composite gels were investigated using mixture design experiments. Gelatine and gellan yielded composite gels that showed different textural behaviours and microstructure. All BCG and TCG blends showed antagonistic effects; the composite gels were softer and weaker as compared to the SCG. Gelatine‐BCG and TCG were comparatively stronger than those of gellan due to their different gelling mechanisms, in which the former had yielded a denser network structures as compared to the latter.     

Gelling properties of whey protein isolate: influence of calcium removal by dialysis or diafiltration at acid or neutral pH

Dialysis of whey protein isolates (WPI) removed much more calcium when carried out at an acid pH (close to 4.0) than at neutral pH. Diafiltration at acid pH was also effective. The characteristics of thermally-induced gels prepared from WPI dialysed at acid or neutral pH were studied at pH 3.75 or pH 7.0, respectively, and at calcium concentrations ranging from 0 to about 60mM (with addition of calcium chloride). The water-holding capacity (WHC) and elasticity of gels increased with decreasing calcium concentration, at both pHs. Gel firmness was maximum at 10–20 mM calcium. The solubility of the protein constituents of WPI gels in a pH 8.0 buffer was high in the case of acid gels (especially at calcium concentrations lower or equal to 20 mM) and low for neutral gels at all calcium concentrations. Protein solubility values in the presence or absence of denaturing and reducing agents reflect the existence of intermolecular disulphide bonds in neutral gels and their absence in acid gels.     

肌球蛋白与胶原蛋白和明胶混合凝胶质构特性的研究

研究了肌球蛋白与胶原蛋白、肌球蛋白和明胶混合凝胶的质构特性和保水性。结果表明:肌球蛋白与胶原蛋白、肌球蛋白与明胶混合凝胶的硬度、弹性和保水性均比纯肌球蛋白高。肌球蛋白与胶原蛋白混合凝胶在pH6.0时,硬度最低、保水性最低,但弹性最大。混合凝胶的硬度和保水性随着离子强度的升高而升高,但弹性则恰好相反。添加KCl能显著改善混合凝胶的弹性,添加SPP和TPP能明显提高保水性。肌球蛋白和明胶混合凝胶在pH6.5时硬度和弹性最大,但保水性在pH6.0时最大;其硬度和弹性随离子强度增加而降低,但其保水性刚好相反。     

Improvement of gelling properties of porcine blood plasma using microbial transglutaminase

The effect of microbial transglutaminase (MTGase) on the texture and water-holding capacity (WHC) of heat-induced gels prepared from porcine blood plasma at pH 5.5 was investigated. Different concentrations of commercial MTGase were added to plasma and incubated for several times under specific conditions of temperature and pH. From the results obtained, it can be postulated that enzymatic treatment enhances textural properties and WHC of plasma gels at pH 5.5, especially when incubated with 3% of the commercial product for 3 h at 30 °C and pH 7. This treatment increased by 0.4 N the hardness of gels and reduced by 3% the water released after gel centrifugation with respect to the control samples. SDS–PAGE confirmed that cross-linking took place when MTGase was added to plasma solutions. However, the results suggest that the sole addition of MTGase was not effective enough to improve the gelling properties of plasma proteins under acidic conditions.     

Factors Affecting the Water-Holding Capacity of Fibrinogen/Plasma Protein Gels Optimized by Response Surface Methodology

ABSTRACT: Response surface methodology (RSM) was applied to optimize the water-holding capacity (WHC) of fibrinogen/plasma protein gels heated at 75°C for 10 min to develop a new edible gel. The effects of varying the amount of fibrinogen, plasma protein, calcium, and pH were evaluated to optimize the WHC using RSM. Estimation of the overall effects of the 4 factors on the gels revealed that the pH and concentrations of fibrinogen and plasma protein significantly affected the WHC of the gels ( p < 0.05). The WHC increases with the concentrations of plasma protein only at concentrations lower than 8%. At lower plasma concentrations, fibrinogen addition had only minimal influence on the WHC. The optimum WHC values were predicted by the RSREG procedure of the SAS program. Model verification was performed by additional independent trials, and the resulting experimental values were very close to the predicted ones with no significant difference ( p > 0.05).     

Strength of Protein Gels Prepared with Microbial Transglutaminase as Related to Reaction Conditions

Influence of gelling reaction conditions on the strength of several protein gels prepared with microbial transglutaminase (TGase) was investigated. A method was developed to gel proteins and measure gel breaking strength in a micro well plate. Enzyme concentration range for maximum gel breaking strength varied from 10 to 40 units/g protein. Maxima gel breaking strengths were achieved at 50°C for SPI, caseinate and gelatin and 65°C for egg yolk and egg white proteins. Optimum pH resulting in strong gels was pH 9 for SPI, caseinate, and egg yolk, and pH 6 for gelatin and egg white. Adjusting pH was promoted in egg white the formation of ?-(γ-glutamyl)lysine crosslinks and increased its gel breaking strength.     

Microstructure–function relationships of heat-induced gels of porcine haemoglobin

The purpose of this work was to use image analysis to study the microstructural properties of haemoglobin gels, with structural changes induced by pH conditions, and their correlations with physical properties such as texture and water holding capacity (WHC). Two types of networks showing great differences in the dimensions of the gel structure were obtained as influenced by pH. At pH < 5.5 there was a shift from an aggregated to a fine-stranded gel type. Fractal dimension values revealed that more complex structures corresponded to softest and non-exudative gels. Lacunarity and pore size, which were used to study the pore distribution within the network, confirmed that softest gels with high WHC showed large number of small cavities. Finally, correlations between textural attributes, i.e. springiness and adhesiveness, and spatial variability, referred quantitatively to the degree of compactness, were also established.     

Influence of pH and Salts on Egg White Gelation

ABSTRACT: Egg white is used in food products for various functional properties. These are strongly influenced by pH, ionic strength, type and concentration of salts. Through an experimental design strategy, the aim of this study was to quantify the influence of pH, cations, and anions naturally present in egg white, and of citrate on egg white gelation. Results showed that pH and Fe³⁺ modified the coagulation temperature of egg white and consequently, the gel characteristics. High concentrations of NaCl decreased the water-holding capacity and the microstructure of egg white gels. At pH 7, viscoelastic properties and microstructure of egg white gels were altered by Ca²⁺ and Mg²⁺ addition.     

Modified Soy Proteins with Improved Foaming and Water Hydration Properties

Soy proteins were modified by alkali treatment at pH 10.0, followed by papain hydrolysis. Solubility, water hydration capacity (WHC), surface hydrophobicity, foaming and emulsifying properties of unmodified, alkali-treated, and papain-modified soy protein (PMSP) were compared. PMSP exhibited higher solubility (100% at pH > 7.0), WHC (3.13) and hydrophobicity (40.8) than unmodified soy protein which had solubility 68.5%, WHC 0.21, and hydrophobicity 8.1. The PMSP had foaming capacity (22.0 mL) similar to egg white (21.2 mL) at pH 7.0; and enhanced foam stability (36.4) compared to the unmodified control (32.9). In general, alkali-treated soy had lower functional properties. Emulsifying properties of PMSP and alkali treated soy were unchanged by the modification. PMSP could be used as an egg white substitute in foaming applications at neutral pH.     

Isostrength Comparison of Large-Strain (Fracture) Rheological Properties of Egg White and Whey Protein Gels

The effects of protein concentration and heating conditions on the physical properties of whey protein isolate (WPI) (in 50 mM NaCl, pH 7) and egg white (pH 9) gels were examined. Egg white and WPI gels had similar values for shear stress at fracture (i.e., isostrength), while trends for shear strain at fracture were protein-type specific. The rigidity ratio (R_0.3), ratio of the rigidity at fracture (G_f) to the rigidity at 30% of fracture strain, measured departure from the stress-strain relationship of an ideal Hookean solid. All gels fit master curves of G_f vs R_0.3, which were described by a power law model of R_0.3=A(G_f)-°19, where "A" showed protein type-specific characteristics.     

非肉蛋白添加对猪肉糜品质及其肌原纤维蛋白结构的影响

将血球蛋白粉（spray-dried blood cells,SBC）、大豆分离蛋白（soybean protein isolate,SPI）、蛋清蛋白（egg white protein,EWP）和猪血浆蛋白（porcine plasma protein,PPP）分别以不同添加量添加至肉糜中,研究其对肉糜品质及其肌原纤维蛋白结构的影响,以未添加非肉蛋白的肉糜为空白对照,以蒸煮损失、色度、pH值、微观结构、质构等为考察指标。结果表明：与空白对照组相比,添加EWP使得猪肉糜呈现疏松多孔结构,导致其保水性降低;而添加PPP能够显著改善肉糜凝胶的保水性、质构特性和微观结构,提高肉糜pH值;质构分析结果表明,非肉蛋白的添加能够显著提高肉糜的咀嚼性;添加SBC使肉糜红度值提高;通过分析肌原纤维蛋白的二级结构发现,加入PPP和SBC组酰胺Ⅰ带最大吸收峰红移,表明α-螺旋含量提高,相应地,无规则卷曲含量下降,导致凝胶结构变致密,凝胶强度与凝胶保水性提高;经非肉蛋白处理的肌原纤维蛋白紫外吸收强度普遍有所降低,紫外吸收光谱图中的最大吸收峰略微红移,表明蛋白质发生聚集。综上所述,添加PPP可有效改善肉糜品质。     

影响猪血浆蛋白热诱导凝胶质构特性及持水性因素的研究

本实验研究在一定的加热条件下猪血浆蛋白质量浓度、加热温度、加热时间、离子种类、离子强度和pH 值对猪血浆蛋白热诱导凝胶的质构、持水性等性质的影响。利用质构仪测定猪血浆蛋白热诱导凝胶的硬度和黏附性,利用离心的方法测定凝胶的持水性。结果表明,在80℃下加热45min,猪血浆蛋白质量浓度超过6g/100mL可以形成凝胶,并且随蛋白质量浓度的增大,凝胶强度和持水性也增大;凝胶强度随pH 值(3～9)增加而增大,pH5 时凝胶的持水性最小,pH3 时最大;NaCl 浓度0.2mol/L,CaCl2 浓度0.6mol/L 时,凝胶硬度最大。实验得出,猪血浆蛋白热诱导凝胶的质构特性及持水性受许多因素影响,在实际生产中应该控制加热条件,以获得高质量的凝胶。     

牛肉排酸成熟过程中的品质变化

为探究排酸成熟过程中肉类品质的变化,以牛肉为研究对象,测定排酸1～7 d肉样的硬度、保水性、pH值、肌原纤维小片化指数（myofibril fragmentation index,MFI）、菌落总数、大肠菌群数以及排酸1、3、5d时肌原纤维的超微结构。结果表明：牛肉排酸3 d时出现最大僵直期,硬度达到最高,保水性达到最低,pH值降到最低值5.56;随着解僵及成熟的进行,牛肉嫩度、保水性回升,排酸7 d时pH值回升到5.84,达到排酸成熟肉标准（5.8～6.2）;排酸1 d时,肌原纤维的Z线、粗细丝清晰可见,随着肌原纤维小片化程度的不断加深,排酸5d时,Z线变得模糊,几乎消失,成为晕染状,几何构型发生明显变化。上述结果表明,牛肉在0～4 ℃条件下排酸成熟需要7d,前3 d是排酸的关键时期。     

Linear Programming and Response Surface Methodology to Optimize Surimi Gel Texture

A formulation optimization study was conducted on surimi gels prepared with starch, and/or raw egg white employing the stepwise method (SM), linear programming (LP), and response surface methodology (RSM). At 78% moisture, the greatest gel strengthening and reduction of expressible moisture occurred at 8% starch, 6% egg white, or a combination of 5% starch and 5% egg white for SM, 5.33% starch and 4.33% egg white for LP, and 3.5% starch and 5% egg white for RSM. RSM resulted in gels with the greatest strength (compressive and penetration forces), followed by LP and SM. The RSM enabled more accurate prediction of textural behavior of final product at various ingredient combinations than the SM or LP.     

Functional Properties of Heat Induced Gels from Liquid and Spray-Dried Porcine Blood Plasma as Influenced by pH

The properties of gels obtained from porcine blood plasma were studied under different pH conditions. Gels from liquid and spray-dried plasma were prepared and analyzed for water holding capacity (WHC), texture, and microstructure at pH 7.4, 6, 5.5 and 4.5. The denaturation extent of proteins was also determined by differential scanning calorimetry (DSC). All properties studied were dependent on pH. The WHC and consistency of gels decreased when pH decreased. These results correlated with microstructural changes observed by SEM. Spray drying affected the consistency of gels. The penetration force of the gel from dehydrated plasma was always lower than that prepared from liquid plasma where the pH was the same, but neither the WHC nor the micro-structure of gels were affected.     

Effect of dietary fibre and MTGase on the quality of mackerel surimi gels

BACKGROUND: The effects of microbial transglutaminase (MTGase; 5 g kg^?1) and dietary fibre (inner pea fibre and chicory root inulin, 20 and 40 g kg^?1) on gels from surimi made with Atlantic (Scomber scombrus) and chub mackerel (Scomber japonicus) were studied with the purpose of achieving a better understanding of the underlying phenomena and improving gels. RESULTS: MTGase addition improved textural properties (namely, cohesiveness increased from 0.19–0.41 to 0.59–0.72) and increased pH and water‐holding capacity (WHC). Moreover, MTGase reduced the elastic and viscous modules and darkened gels; protein solubility declined, meaning greater protein aggregation, according to electropherograms. MTGase had no unequivocal effect upon the gels' microstructure. Pea fibre increased hardness (an increase of almost 60% with 40 g kg^?1) and related parameters, the elastic and viscous modules and WHC. Pea fibre reduced extractable protein in sodium dodecyl sulfate and urea (in the absence of MTGase) as well. Scanning electron microscopy revealed different structures for gels containing pea fibre. Regarding inulin, it worsened textural quality and WHC. CONCLUSION: A combination of MTGase and pea fibre can improve a poor quality surimi. Copyright © 2009 Society of Chemical Industry