乳清蛋白凝胶条件的研究

以乳清蛋白为研究对象，研究了乳清蛋白浓度、温度、加热时间、pH值、金属离子等因素对乳清蛋白凝胶形成的作用。结果显示，乳清蛋白形成凝胶的基本条件是乳清水溶液浓度大于0．133g／mL，温度高于85℃±2℃，当温度在85℃±2℃～90℃±2℃之间，凝胶形成时间随乳清蛋白浓度变大而减少，在沸水中乳清蛋白浓度对凝胶形成时间影响不大，在19min左右；酸性条件下乳清蛋白形成凝胶的最适pH为5．3，pH小于1．2在沸水中加热30min，乳清蛋白形成碎块状凝胶，碱性条件下形成凝胶的最适pH为8．3，pH大于12．8在沸水中加热30min，乳清蛋白变为红色；钙离子的添加可使乳清蛋白形成凝胶所需时间减少到6min。     

pH和金属离子对大豆分离蛋白凝胶形成的影响

在90℃，研究了大豆分离蛋白浓度、pH值、金属离子、加热时间等因素对大豆分离蛋白凝胶形成的作用。结果显示，酸性条件下大豆分离蛋白形成凝胶的最适pH为3．0，碱性条件下形成凝肢的最适pH为9．0,pH大于11在95℃的水浴锅中加热5min，大豆分离蛋白变为黄棕色粘稠状液体，且有异味；凝胶溶液中CaCl2浓度为0．4％时，形成凝胶的透明性最高，时间为22min。     

pH和金属离子对大豆分离蛋白凝胶形成影响

在90℃,研究大豆分离蛋白浓度、pH值、金属离子、加热时间等因素对大豆分离蛋白凝胶形成影响。结果显示,酸性条件下大豆分离蛋白形成凝胶最适pH为3．0,碱性条件下形成凝胶最适pH为9．0,pH大于11在95℃水浴锅中加热5 min,大豆分离蛋白变为黄棕色粘稠状液体,且有异味;凝胶溶液中CaCl2浓度为0．4％时,形成凝胶透明性最高,时间为22min。     

马铃薯分离蛋白凝胶的制备及其性质研究

以新鲜马铃薯为原料,采用等电点沉淀法制备马铃薯分离蛋白。确定了马铃薯分离蛋白最低凝胶点的蛋白质浓度为6%。考察蛋白质浓度、pH 值、加热温度和加热时间4 个因素对凝胶形成的影响,采用物性仪对不同条件下制备凝胶的质构特性进行研究,通过脆度、硬度、稠度、黏聚性和黏着性这5 个指标对马铃薯分离蛋白的质构特性进行说明。优化结果表明不同评价指标得出的结论不尽相同。对马铃薯分离蛋白凝胶特性进行综合评价,可选用蛋白质浓度12%、pH7.0、加热温度95℃、加热时间15min 制备凝胶。     

pH和金属离子对大豆分离蛋白凝胶形成的影响

在90℃,研究了大豆分离蛋白浓度、pH值、金属离子、加热时间等因素对大豆分离蛋白凝胶形成的作用。结果显示,酸性条件下大豆分离蛋白形成凝胶的最适pH为3.0,碱性条件下形成凝胶的最适pH为9.0,pH大于11在95℃的水浴锅中加热5min,大豆分离蛋白变为黄棕色粘稠状液体,且有异味;凝胶溶液中CaCl2浓度为0.4%的时,形成凝胶的透明性最高,时间为22min。     

蛋清蛋白质凝胶质构特性的研究

蛋清蛋白质因具有良好的凝胶性能在肉制品、方便面等食品中有很好的应用,研究其凝胶质构特性可以为蛋清粉在这些食品中的应用提供重要的理论参考。本研究以蛋清粉为原料,通过旋转正交实验设计,研究蛋白质浓度、蛋清溶液的pH、加热温度、加热时间对凝胶形成的影响,采用物性仪对凝胶的质构特性如凝胶硬度和弹性进行了测定。结果表明,形成凝胶硬度最大的制备条件为:蛋白质浓度19%、蛋清溶液的pH5.5、温度85℃、加热时间55min;形成凝胶弹性最大的制备条件为:蛋白质浓度19%、蛋清溶液的pH6.0、温度78℃、加热时间40min。     

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。     

大豆分离蛋白浓度和温度对凝胶形成的影响

以大豆分离蛋白为原料,研究了蛋白浓度、温度、加热时间等因素对大豆分离蛋白凝胶形成的影响.结果显示,大豆分离蛋白形成凝胶的最佳条件是大豆分离蛋白水溶液浓度为16%,温度90℃,凝胶形成时间为23min,当温度在85℃～95℃之间,凝胶形成时间随大豆分离蛋白浓度变大而减少.在沸水中,由于气泡产生而无法形成凝胶.温度高于85℃会使凝胶颜色加深.     

大豆11S球蛋白凝胶形成的影响因素分析

以低温脱脂大豆粕为原料,采用等电点冷沉法浸提11S球蛋白。对11S球蛋白凝胶形成过程中影响凝胶质构的因素进行了分析,研究表明,11S球蛋白凝胶形成时蛋白浓度、加热温度、加热时间、蛋白溶液pH对凝胶质构均有一定的影响。采用正交实验设计,通过质构仪进行物性测定比较其凝胶性,大豆11S球蛋白浓度14%、加热温度90℃、溶液pH为7、加热时间60min条件下形成的凝胶强度最好,其凝胶面积410.30g·s,凝胶力117.9g。     

大豆蛋白凝胶制备及其性质研究

研究以NaCl作为凝固剂,将大豆分离蛋白(SPI)80℃预热处理10 h,在不同浓度、离子强度及pH值条件下,通过95℃加热蛋白液30min使蛋白变性来制备大豆蛋白凝胶,并对凝胶的质构及凝胶特性进行了分析。结果表明:pH值7.0、80℃预热处理10 h的大豆蛋白溶解性明显小于普通SPI,其他pH值条件下两者溶解性差异不大;pH值2.0、80℃预热处理10 h的蛋白凝胶情况明显优于普通SPI,在一定范围内,随着蛋白浓度及离子强度的增加,凝胶情况越来越好。     

Comparison of Transparent Gels with Turbid Gels Prepared from Egg White: Creep Analysis of Gels

Egg white from which the precipitate occurring during dialysis against water had been removed gave a transparent gel on heating at lower salt concentrations and pH 3.54. The addition of NaCl or a shift of pH from 3.54 to 4.50 brought about the turbid gels. Creep analyses of these transparent and turbid gels were done using a four-element mechanical model. The instantaneous elastic modulus, E₀, Newtonian modulus, ηn and retarded viscoelastic moduli, E₁ and η₁ increased with NaCl up to 125 mM and then decreased with increase in NaCl concentration at pH 3.54. At 125 mM NaCl and pH 3.54, a translucent gel was obtained. E₀ and η₁ decreased with the temperature of the gel, while E₁ and η₁did not change depending of temperature.     

Fracture Analysis of Alginate Gels

The fracture properties of alginate gels were investigated using torsion and compression. The gel fracture stress correlated with Ca²⁺ and alginate concentration, whereas the fracture strain was insensitive to composition. Considering the relationship of fracture stress with gel network crosslink density and the energy to break covalent and noncovalent bonds, the fracture of alginate gels is hypothesized to result from the disruption of junction zones. Consequently, the fracture stress was the stress required to overcome electrostatic forces that formed junction zones. The fracture stress‐strain relationship for alginate gels can be described by the Blatz, Sharda, adn Tschoegl (BST) equation, suggesting that for a given gel, the fracture strain can be predicted based on fracture stress, small‐strain shear modulus, and a fitted parameter describing nonlinearity of the gel. In addition, the fracture properties were affected by deformation rate. The influence of deformation rate on fracture was ascribed to structural changes among the alginate junction zones.     

莲子淀粉凝胶力学性能影响因素的研究

研究不同淀粉乳浓度、pH 值、NaCl 浓度、糖的种类以及吐温-80 浓度对莲子淀粉凝胶力学性能的影响。结果表明：随着淀粉乳浓度的增加,淀粉凝胶强度和弹性模量呈线性关系增加,而凝胶弹性增加不明显;随着NaCl 添加量的增加,淀粉凝胶强度和弹性模量呈先增大后减小的趋势,凝胶弹性则呈减小的趋势;在pH4.0～7.2范围内,淀粉3 种凝胶力学性能变化趋势与不同NaCl 浓度下的变化相反;3 种糖类物质均可提高莲子淀粉的凝胶强度,其大小顺序依次为果糖＞葡萄糖＞蔗糖,同时也可提高莲子淀粉的凝胶弹性和弹性模量,但影响程度不大;当吐温-80 加入量小于0.5% 时,淀粉凝胶强度和弹性模量迅速减小,凝胶弹性略有增加,当吐温-80 加入量大于0.5% 时,淀粉凝胶力学性能基本不变。     

Structural Characterization of Amaranth Protein Gels

ABSTRACT: Gelation capacity of a native amaranth protein isolate was studied. Structural properties of gels prepared at different protein concentration and heating conditions were analyzed. Proteins present in amaranth isolates obtained by water extraction at pH 9.0 and subsequent isoelectric precipitation are able to form gels of yellowish appearance. Gel color intensity increased while luminosity decreased with increasing protein concentrations. High protein concentration allowed the formation of matrices with high water-holding capacity. In addition, increasing the heating temperature resulted in gels of high luminosity and low water-holding capacity. The increase of protein concentration (10% to 20% w/v) as well as the increase of heating temperature (70°C to 95°C) and heating time (10 to 30 min) resulted in the formation of a more ordered matrix with smaller pores, mainly stabilized by disulfide bonds and, at a lower extent, by noncovalent interactions (specially hydrogen bonds and hydrophobic interactions). Both amaranth globulin (11S globulin and P globulin) participated in gel structure via high-molecular-weight aggregates (>100 kD). Gel structure was stabilized via noncovalent bonds by monomer species of 42 kD and those of molecular mass lower than 20 kD localized in the interstitial spaces of gel matrix.     

Stress Relaxation of Acid-induced Milk Gels

The effects of the addition of sugar (sucrose) or salt (KCl/NaCl mixture) on the rheological properties of acid milk gels formed under different process and composition conditions were studied using an experimental design and surface response analysis. The variables evaluated were: sodium caseinate, whey protein concentrate, carrageenan, sucrose or KCl/NaCl concentration, and the mixing temperature of the components. The stress relaxation measurements were made within the linear viscoelasticity domain, and the data obtained were fitted to the generalized Maxwell model. Five parameters were obtained from the fitting: three elastic elements and two viscous elements. In addition, the denaturation process of whey protein with different solute concentrations was evaluated using differential scanning calorimetry. Denaturation temperature increased with increases in the solute concentrations, but enthalpy values did not change independent of solute type and concentration. The results showed that the elastic and viscous moduli increased with sucrose concentration, i.e., the gel network was reinforced, while the opposite occurred with the addition of the saline mixture. Increasing ionic strength of saline mixture and the process temperature were the more important effects with respect to the rheological properties of gels with added saline mixture. On the other hand, the biopolymer concentrations showed the most significant effects on the properties of gels with added sugar.     

Diffusion of Glucose in Carrageenan Gels

From an experimental set-up with boundary conditions of an extended initial distribution the diffusion coefficient for glucose in a high K-content carrageenan gel was evaluated as a function of the carrageenan concentration (1, 2 and 4%) and temperature (0.0, 5.0, 10.0, 15.0, 25.0, and 36.0°C). According to an Arrhenius-type equation, the activation energies at 1, 2 and 4% of carrageenan were calculated as 18.1, 17.4, and 19.1 kJ/mol. From these data it was concluded that carrageenan affects diffusion mainly by an obstruction effect.     

Heats of Dehydration of Starch Gels

Integral heats of dehydration have been measured by simultaneous differential thermal analysis (D.T.A.) and thermogravimetric analysis (T.G.A.) for gels of wheat starch. The results are interpreted on the basis that removal of water involves three structural changes: (a) Breakdown of starch-water interaction (endothermic); (b) Breakdown of water-water interaction (endothermic); (c) Increase in starch-starch interaction (exothermic). On balance, the overall process is endothermic. It has also been shown qualitatively that the formation of gels from starch and water is an endothermic process. It is suggested that the energy required to disrupt the structure of the starch granules during gelation is greater than the energy released by increased starch hydration.     

Flow Behavior of Mixed-Protein Incipient Gels

Strong protein gel networks may result from synergistic interactions with other proteins or food materials above that are not achievable with a single protein alone. The varying flow and viscoelastic behavior of calcium caseinate or whey protein isolate mixed with egg albumin, fish protein isolate, soy protein isolate, or wheat gluten in a model system with wheat flour and glycerol as starch and oil surrogates was determined. Temperature sweeps revealed peak tan δ values as the proteins aggregated. Single protein gels of calcium caseinate, soy protein isolate, and wheat gluten were predominantly elastic, while egg albumin and whey protein isolate gels were mostly viscous. For example, egg albumin steady shear viscosities were: 0.0145 Pa s (0.5 min) and 0.1331 Pa s (45 min), and whey protein isolate 0.0003 Pa s (0.5 min) and 0.0024 Pa s (45 min); but combined with whey protein isolate (whey protein isolate/egg albumin: 10/5 wt%), the apparent viscosity values dropped to 0.0053 Pa.s (0.5 min) and 0.0221 Pa s (45 min), respectively.     

Penetration Studies of Blood Globin Gels

Studies were made on the effect of temperature, pH and protein and salt concentration on the penetration force withstood by globin gels. The registered force increased with heating temperature (60 - 95°C) and protein concentration (1.4 - 5.0%). The gelation pH was dependent on both protein and salt concentration; the higher the protein or salt concentration the lower the gelation pH. At 3% protein concentration globin formed a gel around pH 5 - 6. At 0.7% concentration and higher, the presence of salt weakened the gel strength, while the addition of plasma increased the gelation pH of salt-containing globin gels. A substantially higher penetration force was measured for bovine globin gels than porcine globin gels. Further concentration and spray-drying decreased the gel strength of globin gels.     

Elastic Attributes of Heated Egg Protein Gels

The equilibrium stress of egg white (EW) and ovalbumin (OV) gels using the statistical theory of rubber elasticity suggested that 3.9 covalent disulfide cross-links per OV molecule were formed on gelling. DTNB and PCMB reacted with approximately 4 sulfhydryls of OV in 2% SDS and/or at 82°C. Moreover, the equivalent of 3 secondary bonds, calculated from the initial stress and presumably a composite of numerous weak secondary bonds, contributed significantly to the protein gel stress.