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。     

Formation of Elastic Whey Protein Gels at Low pH by Acid Equilibration

Abstract: Whey protein gels have a weak/brittle texture when formed at pH ≤ 4.5, yet this pH is required to produce a high-protein, shelf-stable product. We investigated if gels could be made under conditions that produced strong/elastic textural properties then adjusted to pH ≤ 4.5 and maintain textural properties. Gels were initially formed at 15% w/w protein (pH 7.5). Equilibration in acid solutions caused gel swelling and lowered pH because of the diffusion of water and H⁺ into the gels. The type and concentration of acid, and presence of other ions, in the equilibrating solutions influenced pH, swelling ratio, and fracture properties of the gels. Swelling of gels decreased fracture stress (because of decreased protein network density) but caused little change to fracture strain, thus maintaining a desirable strong/elastic fracture pattern. We have shown that whey protein isolate gels can be made at pH ≤ 4.5 with a strong/elastic fracture pattern and the magnitude of this pattern can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time. Practical Application: Low-pH shelf-stable whey protein gels having the strong/elastic texture can be made by forming gels at high pH and equilibrating in acid solutions. Acid equilibration causes the gel to swell and lower the gel pH. Moreover, gel properties can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time.     

Effect of Sucrose Addition and Heat Treatment on Egg Albumen Protein Gelation

ABSTRACT: Studies were conducted to evaluate the effect of sucrose (0% to 60% w/w) on the heat denaturation and gelation of egg albumen solutions (pH 7.0) by thermal analysis and rheological measurements. Temperature and frequency sweeps were carried out under small deformations to determine the temperature at which structure development began (T_s) and the storage modulus plateau (G₀), respectively. The latter was used to estimate the molecular weight of the internal chains between cross-links (M_c) using the rubber elasticity theory. Gels were prepared under several heat intensities (70, 80, and 90°C/30 min), and the mechanical properties were determined under small (stress relaxation) and large (stress and strain at fracture) deformations. It was observed that increments in sucrose concentration could act in the stabilization of the proteins, promoting a significant increase in the onset values and temperature of denaturation. The gelling process showed aT_s increase with higher sucrose concentration. Gelation and the gel mechanical properties and network density showed a strong dependence on sucrose concentration and heat treatment temperature. In a general way, the sucrose promoted an improvement in the gel network up to a determined value of sugar concentration. At higher sugar concentrations, the values for the rheological properties decreased, which could be related to an incomplete unfolding of the oval-bumin under these conditions.     

VISCOELASTIC PROPERTIES OF WHEY PROTEIN CONCENTRATE GELS WITH HONEY AND WHEAT FLOUR AT DIFFERENT pH

Viscoelasticity of heat-induced gels from whey protein concentrate, with different contents of honey and wheat flour, and prepared at pH 3.75, 4.2 and 7.0, was studied by using dynamic rheological assays. The elastic modulus of gels prepared at neutral pH was higher than the corresponding to acidic gels, probably due to the fact that sulphydryl-disulfide interchange reactions are favored at neutral pH. Honey decreased the elastic modulus and increased the viscous modulus and the complex viscosity in all conditions assayed. Wheat flour increased the elastic modulus, and all samples exhibited a gel-type behavior except at high honey content.

PRACTICAL APPLICATIONS

Honey and wheat flour modifies the properties of whey protein concentrate gels. Both components have opposite effects: honey increases the viscous-like behavior and wheat flour the solid-like behavior of gels in all conditions assayed. The different characteristics of gels prepared at different pHs and with different amounts of honey and wheat flour could be used in different formulated foods, as desserts.     

牛血浆蛋白凝胶特性研究

研究不同加工条件如蛋白浓度、加热温度、离子强度和pH对牛血浆蛋白凝胶特性的影响。结果表明:蛋白浓度的提高有利于凝胶的形成,且形成凝胶的最低血浆蛋白浓度是4.0%;4.8%的血浆蛋白,线性升温到85℃保温20 min,能够很好形成凝胶,呈果冻状,光滑有弹性;NaCl浓度在1.0 mol/L以下时,血浆蛋白凝胶强度随离子强度的变化是先增加后减小,0.3 mol/L时取得最佳效果;在pH6.0~9.0范围内,pH为9.0时牛血浆蛋白凝胶的凝胶强度较好,保水性高,蒸煮损失低。NaCl和pH对于牛血浆蛋白的凝胶特性有极显著的互作效应。     

Rheology of Rice Starch‐Sucrose Composites

The effect of sucrose at different concentrations (0, 10, 20 and 30%) on rheological properties of rice starch pastes (5% w/w) was investigated in steady and dynamic shear. The steady shear properties of rice starch‐sucrose composites were determined from rheological parameters for power law and Casson flow models. At 25°C all the starch‐sucrose composites exhibited a shear‐thinning flow behavior (n=0.25–0.44). The presence of sucrose resulted in the decrease in consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc). Dynamic frequency sweeps at 25°C indicated that starch‐sucrose composites exhibited weak gel‐like behavior with storage moduli (G′) higher than loss moduli (G′′). G′ and G′′ values decreased with the increase in sucrose concentration. The dynamic (η*) and steady‐shear (η_a) viscosities at various sucrose concentrations did not follow the Cox‐Merz superposition rule. G′ values as a function of aging time (10 h) at 4°C showed a pseudoplateau region at long aging times. In general, the values of G′ and G′′ in rice starch‐sucrose composites were reduced in the presence of sucrose and depended on sucrose concentration.     

美藤果蛋白的功能性质研究

以美藤果饼为原料,采用碱提酸沉法制备美藤果蛋白,研究pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白功能性质的影响。结果表明:当pH为5时,美藤果蛋白的溶解度、乳化性能和起泡性均最小;随着温度的升高,美藤果蛋白的溶解度、持水性、持油性呈先增大后减小的趋势;加入适量NaCl可增大美藤果蛋白的溶解度、乳化性能和起泡性能;加入蔗糖使美藤果蛋白的起泡性降低,而加入适量的蔗糖可增大美藤果蛋白的乳化性能。pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白的功能性质有一定影响,可通过改变上述条件以获得良好加工性质的美藤果蛋白产品。     

Rheological properties of Salecan as a new source of thickening agent

Salecan is a novel soluble glucan produced by Agrobacterium sp. ZX09, displaying the ability to inhibit pancreatic amylase and reduce postprandial glucose. The research here provides an investigation of the rheological properties of Salecan solution over a wide range of shear rate (0.001–1000 s⁻¹), frequency (0.1–100 rad/s), concentrations (0.3%, 0.5%, 1.0% and 1.5%), temperature (5–95 °C) and pH (1.0–13.0). The power law model well described the rheological behavior of the solutions, in the shear-thinning region, with high determination coefficients, R². Salecan solutions showed a non-Newtonian viscosity behavior at all concentrations and temperatures. The solutions exhibited excellent stability below 55 °C. Viscosities were not affected after being frozen (−20 °C). Over a wide pH range from 6.0 to 12.0, the viscosity almost kept invariant. With increasing frequency, the storage and loss moduli G′ and G″ of Salecan solution increased and complex viscosities decreased continuously, which showed an elastic behaviour. All data indicated that Salecan has excellent rheological properties and could be utilized in food industry as a new source of thickening agent.     

Copper Activity in Sucrose Solutions

Copper activity was measured by a cupric electrode in 0.1 M sodium acetate-acetic acid buffered (pH 3.2, 4.5, 6.0) and unbuffered sucrose solutions (10% w/v) using the standard addition technique (l–10 ppm of Cu⁺⁺). In water, the measured copper concentration (activity) was linearly related to the added copper concentration with a slope of unity. The slope decreased in acetate buffer solutions as pH increased indicating that Cu⁺⁺ was complexed with acetate and to a greater extent at higher pH. In the presence of sucrose, copper activity increased approximately 16% in all solutions. Results suggest that the bulking effect of sucrose and the decreased water activity in solutions produced increased copper activity in sucrose solutions.     

Flow Properties of Solutions of Oat β-Glucans

The flow properties of aqueous solutions of oat β-glucans were studied using a Bohlin rheometer (concentric cylinder geometry) over the shear rate range 0.734–1500 1/sec at temperatures between 15 and 75 °C. The β-glucan powder concentrations employed were 0.20–1.56% (w/w). The power law model was satisfactory for describing the flow behavior of β-glucans over the shear rate range 18.6–232 1/sec. The magnitudes of activation energy were in the range 2.41–4.61 (kcal/ mol). Sucrose decreased the flow behavior index and increased the consistency index of β-glucans and decreased the activation energy at lower β-glucan concentrations, these effects being most pronounced at a sucrose concentration of 25%. The D-value for solutions of β-glucans (0.65%) at 100 °C was 145 hr.     

Viscoelastic Characterization of Sage Seed Gum

Wild sage seed is a small, rounded, and mucilaginous seed, which comes from Salvia macrosiphon. The viscoelastic behavior of sage seed gum, at different concentrations (0.5–2%, w/w), was examined by measuring the transient (in-shear structural recovery and creep/recovery tests) and dynamic (stress and frequency sweeps) rheological properties. The mechanical spectra showed typical weak gel behavior at all concentrations, with storage modulus higher than loss modulus, and little variation with frequency. Both moduli greatly increased with increasing the concentration, and the concentration dependency was well described by the power-law model. The loss tangent was increased slightly with increasing the frequency in the range of 0.25–0.67, although it was not affected by an increase in gum concentration. Moreover, the complex viscosity was found to increase with the increase of sage seed gum concentration and to decrease linearly with the increase of frequency. All samples showed typical viscoelastic response to stress in creep/recovery tests, with recoverable strain increasing in direct proportion to sage seed gum concentration. Creep curves were adequately fitted with a Burger model of four parameters. The elastic and viscous contributions to the general viscoelastic behavior were analyzed through the obtained parameters. The concentration had no specific effect on the in-shear recovery properties of sage seed gum gels, and the gel structure was highly recovered after applying shear. The results of this article indicated that sage seed gum may offer an excellent alternative for commercial gums as a thickening/gelling agent.     

Influence of sucrose on NaCl-induced gelation of heat denatured whey protein solutions

A solution of heat-denatured whey proteins was prepared by heating 10 wt.% whey protein isolate at pH 7.0 to 80°C for 10 min in the absence of salt. This treatment caused the globular protein molecules to partially unfold and aggregate. When the heat-denatured whey protein solution was cooled to room temperature and mixed with 200 mM NaCl it formed a gel. The influence of sucrose (0 to 10 wt.%) in the protein solutions prior to NaCl addition on the gelation rate was investigated. At relatively low concentrations (0–8 wt.%) sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (> 8 wt.%) sucrose increased the gelation rate, probably because it decreased the thermodynamic affinity of the globular proteins for the aqueous solution, which increased the attraction between proteins. This data has important implications for the application of cold-setting whey protein ingredients in sweetened food products such as deserts and beverages.     

Highly acetylated pectin from cacao pod husks (Theobroma cacao L.) forms gel

A pectin (OP) obtained from cacao pod husk with a high acetyl content, which is a structural feature that could disturb the pectins' gel formation, was able to form gels at low pH and a high sucrose content. Pectin gels (1.32% GalA equivalent, w/w) were prepared at pH 2.5–3.3 in the presence of 60% sucrose (w/w). Rheological analyses were performed to determine the optimal pH for further studies. Next, the OP samples were prepared at pH 2.7 in concentrations ranging from 0.33 to 1.98% GalA (w/w) with 60% sucrose (w/w) and subjected to rheological analysis. Dynamic oscillatory experiments at 25 °C indicated the presence of gels for all of the analysed concentrations. Measurements of the elastic (G′) and viscous (G″) moduli at 25 °C also indicated that increasing the pectin concentration resulted in stronger gels. Rotational experiments revealed a shear-thinning behaviour in which the apparent viscosities of the samples increased as the concentration increased. Although the OP had a high degree of acetylation, this pectin was able to form gels, which suggests its potential for use as a gelling and thickening additive.     

阿拉伯胶对马铃薯淀粉糊化及流变性质的影响

研究了阿拉伯胶对马铃薯淀粉糊化及流变性质的影响,考察了马铃薯淀粉/阿拉伯胶混合体系在盐、柠檬酸、糖等不同介质下的糊化性质.RVA结果表明在水溶液中随着阿拉伯胶含量的增加,混合体系的峰值黏度显著降低,具有更好的热稳定性,但在冷却过程中,淀粉黏度明显上升,回值略有增加.添加胶体后,马铃薯淀粉在盐溶液及柠檬酸溶液中的峰值黏度稍有降低,在糖溶液中则表现出更高的黏度.静态流变实验显示不同混合体系均表现出剪切变稀性,添加胶体后,体系假塑性增强,滞后环面积明显减小.     

Effect of CMC Molecular Weight on Acid‐Induced Gelation of Heated WPI‐CMC Soluble Complex

Acid‐induced gelation properties of heated whey protein isolate (WPI) and carboxymethylcellulose (CMC) soluble complex were investigated as a function of CMC molecular weight (270, 680, and 750 kDa) and concentrations (0% to 0.125%). Heated WPI‐CMC soluble complex with 6% protein was made by heating biopolymers together at pH 7.0 and 85 °C for 30 min and diluted to 5% protein before acid‐induced gelation. Acid‐induced gel formed from heated WPI‐CMC complexes exhibited increased hardness and decreased water holding capacity with increasing CMC concentrations but gel strength decreased at higher CMC content. The highest gel strength was observed with CMC 750 k at 0.05%. Gels with low CMC concentration showed homogenous microstructure which was independent of CMC molecular weight, while increasing CMC concentration led to microphase separation with higher CMC molecular weight showing more extensive phase separation. When heated WPI‐CMC complexes were prepared at 9% protein the acid gels showed improved gel hardness and water holding capacity, which was supported by the more interconnected protein network with less porosity when compared to complexes heated at 6% protein. It is concluded that protein concentration and biopolymer ratio during complex formation are the major factors affecting gel properties while the effect of CMC molecular weight was less significant.     

乳清蛋白质浓缩物的流变学性质

本研究以3种工业化生产的乳清蛋白浓缩物(WPC)的再制溶液为对象,测定其不同条件下的流动特性,即在剪切速率3～1321/sec、温度5～65℃、总固形物浓度5～40％,pH3～10等条件下,溶液的剪切应力与剪切速率和剪切应力与剪切时间的关系。WPC溶液的流变学行为与溶液的浓度、温度、pH有关。在多数实验条件下,WPC溶液具有假塑性液体性质,可以用幂律模式(power law module)来表示,在极端条件下,溶液的流动特性则接近牛顿液体或塑性液体。     

A COMPARISON OF THE VISCOELASTIC PROPERTIES OF CONVENTIONAL AND MAILLARD PROTEIN GELS

The properties of gels prepared by heating solutions of bovine serum albumin (BSA) for 30 min at 121C in the presence and absence of glucono-delta-lactone (GDL gels) and xylose (Maillard gels) were compared. During formation the pH of the Maillard and GDL gels decreased to 4.9 whereas the pH of the gels formed in the absence of GDL or xylose remained near neutral. Maillard gels show much less syneresis compared with the GDL gels and contained nondisulphide covalent crosslinks as evidenced by very low protein solubilities in mixtures of sodium dodecyl sulphate and β-mercaptoethanol. Both the GDL and Maillard gels could be formed at much lower protein concentrations than the neutral conventional gels. The stress relaxation of the gels in compression was measured and the response analyzed using Peleg's equation. The parameters in this equation were not strongly dependent on protein concentration or degree of deformation. The neutral pH gels were far more elastic than the low pH gels, but despite the difference in crosslinking mechanisms the viscoelastic behaviour of the Maillard and GDL gels was similar. However, the break strength and asymptotic residual modulus of the Maillard gels were higher. It is suggested that the stress relaxation occurs in weaker, noncovalently linked regions of the gel, whereas the nondisulphide covalent crosslinks in the Maillard gels reinforce strong regions already containing disulphide linkages.     

Effect of Soluble Solids Concentration and Temperature on Thermo-Physical and Rheological Properties of Mango Puree

Thermo-physical and rheological properties of mango pulp were evaluated at different temperatures (20, 40, 60, and 80°C) and total soluble solids concentrations (15, 20, 32, and 40°Brix). Thermal properties were primarily dependent on the moisture content of the sample, and increased with temperature and decreased with soluble solids concentrations. Density showed a reverse trend. Glass transition temperatures increased with an increase in soluble solids concentrations indicating better stability. Empirical models developed for each thermal property as a function of temperature and soluble solids concentrations (R² > 0.90) generally showed better predictions than published models. Mango puree exhibited pseudo-plastic behavior during steady shear measurements, and the power law model well described their flow behavior. Consistency coefficient increased with soluble solids concentrations and decreased with temperature. The flow behavior index ranged between 0.27 and 0.38 but did not show a clear trend either with soluble solids concentrations or temperature. Small amplitude oscillatory shear measurements revealed that mango puree behaved like a weak gel and demonstrated visco-elastic properties.     

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。     

Gel Characteristics—Structure as Related to Texture and Waterbinding of Blood Plasma Gels

Heat induced denaturation and aggregation of plasma protein solutions were studied by low shear viscometry and turbidity measurements. The microstructure of blood plasma gels was evaluated by scanning electron microscopy (SEM). Relationships between gel structure, texture, and waterbinding properties of blood plasma gels prepared under various conditions such as different heating temperatures, pH and protein and salt concentrations were investigated. Generally, it was found that the degree of elasticity and waterbinding properties decreased with an increasing degree of random aggregation of the protein gel network. The degree of aggregation increased with increasing protein and salt concentration and decreasing pH from 9 to 6. With increasing heating temperature from 77° C to 92° C, a partial disruption of the gel structure due to local aggregation phenomena was demonstrated by SEM micrographs.