Microwave Heating of Agar Gels Containing Sucrose

A mathematical model was developed for predicting the temperature profiles of cylindrical samples of sucrose containing agar gels heated by microwaves. Temperature was modeled in terms of dielectric properties of gels and the power absorbed by the sample. Experimental corroboration of the predicted temperatures was obtained by microwave heating cylindrical gels of 2% agar containing 0, 40, and 60% sucrose. The levels of sucrose in the gels notably affected the temperature profiles in the cylinders. Samples with no sucrose showed a pronounced central heating effect, 40% sucrose samples showed a early uniform heating profile and 60% sucrose samples showed surface heating.     

A Modified Maxwell and a Nonexponential Model for Characterization of the Stress Relaxation of Agar and Alginate Gels

Compressive stress relaxation curves of agar and alginate gels of different gum concentration (1–3% and 0.5–2%, respectively) were fitted by a two parameter nonexponential empirical model and a three term modified Maxwell model with two fixed relaxation times (10 and 100s). The asymptotic portion of the residual (unrelaxed) stress calculated by the two models for each gel had a similar magnitude, and therefore could serve as an objective measure of the gels degree of solidity. The coefficients of the modified Maxwell model provided a simple but meaningful means to compare, in quantitative terms, the differences in the relaxation time spectra that were associated with the gels' stiffness and strength.     

Component Flows and Interactions in Agar Gels Predicted by Linear Irreversible Thermodynamics

Equations derived from the linear irreversible thermodynamics showed direct relationships between flow, pressure and chemical potential gradients. To predict flows, three coefficients (hydraulic permeability, solute permeability, and reflection coefficient) were introduced into the equations and measured experimentally for counter-current transfer of water and salt in agar gels. The reflection coefficient was less than 0.0003 indicating that the gel behaved as a non-selective membrane. To analyse the interactions, three interaction coefficients, for solute and water, solute and polymer network and water and polymer network were used, and expressed as a function of the former coefficients. Results showed that only salt and water interactions controlled the rate of transfer.     

Proton NMR and Dielectric Measurements on Sucrose Filled Agar Gels and Starch Pastes

Low-field proton NMR and high-frequency dielectric measurements were performed on sucrose-filled agar gels of 0 to 1.2g sucrose/g water and starch pastes of concentrations between 0.2 and lg starch/ g water. The dielectric constant decreased linearly with increasing concentration for both. The dielectric loss of sucrose-filled agar gels showed two regions, first increasing and then decreasing with concentration. The dielectric loss data for starch pastes showed a constant value close to that of pure water throughout the concentration range. Dielectric data were related to hydration models derived from proton NMR measurements.     

Effects of Shape and Size of Agar Gels on Heating Uniformity During Pulsed Microwave Treatment

Model gel systems with different shape (sphere, cylinder, and slab) and size (180 and 290 g) were prepared with agar (5%) and sucrose (5%). Dielectric constant (ε′), loss factor (ε″), thermophysical properties, and temperature distribution of the model system were measured. Each agar model system was immersed and suspended in water, and then, heated in a microwave oven with intermittent heating until the core temperature reached 50 °C. The ε′ and ε″ of agar gels decreased when frequency increased. The density and thermal conductivity values of the agar gels were 1033 kg/m³ and 0.55 W/m °C, respectively. The temperature distribution of sphere, cylinder, and slab was different when similar power doses were applied. The slab reached 50 °C in less time (10 min) and showed a more uniform heating than spheres and cylinders in both sizes. Agar model systems of 180 g heated faster than those of 290 g. The coldest point was the center of the model systems in all studied cases. Shape and size are critical food factors that affect the heating uniformity during microwave heating processes.     

琼脂—聚内烯酰胺凝胶固定化干酪乳杆菌生产乳酸

将干酪乳杆菌(Lactobacillus Ceasei)细胞固定有琼脂——聚丙烯酰胺凝胶内,用于生产乳酸。研究了底物浓度,酵母膏浓度,培养温度等因素对固定化细胞生产乳酸的影响。对置换发酵过程中固定化细胞的活性及操作稳定性也进行了研究。     

Shear Stress Relaxation of Native and Modified Potato Starch Gels

Shear stress relaxation measurements were used to characterize native potato starch gels, and modified gels, such as starch acetate, distarch phosphate, dihydroxypropyl distarch phosphate and lipid coated starch. It was found that cross-linking and lipid coating greatly increased the stiffness of the gels, which was observed as increased relaxation modulus (G). These gels behaved like viscoelastic solids, which was observed as increased relaxation times (T½) and increased apparent residual moduls (G∞). During ageing, an increase in G and T½ as well as in G∞ was observed for the native starch, the starch acetate and the distarch phosphate. The hydroxypropoyl distarch phosphate and the lipid coated starch were very stable during ageing. To interpret the results in terms of the structure of the starch gel, the gel was described as a composite material, and the stress relaxation results were discussed according to a cooperative theory of flow.     

琼脂甜米酒的试制

琼脂甜米酒是以甜酒酿均质后酒基,加入１．２‰的琼脂,经灭菌处理而成,该产品介科于酒与饮料是,酷似浓牛奶,既保留了甜酒酿的风味特色和营养成分,又保留了琼脂的保健功效。     

GDL诱导改性大豆分离蛋白凝胶溶胀性的研究

讨论了乙二胺四乙酸二酐(EDTAD)改性大豆分离蛋白的制备条件,研究了葡萄糖酸内酯(GDL)诱导该改性大豆分离蛋白凝胶的溶胀性。得出2%SPI适宜的改性条件是:pH 12,温度65℃,改性大豆蛋白时EDTAD为0.6%条件下,所制备的凝胶在GDL为1.2%,所得到的凝胶溶胀率最好,并且该凝胶具有一定的pH响应性。     

Quality of Reduced-Fat Frankfurter Modified by Konjac–Starch Mixed Gels

ABSTRACT:  Konjac–potato starch mixed gels were incorporated into reduced-fat (18%) frankfurters and compared with reduced-fat (18% fat, C18) and high-fat (28% fat, C28) controls for textural, sensory properties, and storage stability. At the same konjac concentration, increasing starch level resulted in lower G' (storage modulus) and G" (loss modulus) of the konjac–potato starch mixtures leading to more elastic-mixed gels. No differences in textural hardness among gel-added treatments were noticed. C28 had the lowest sensory firmness and highest juiciness scores. C18 and gel-added treatments had similar juiciness and firmness scores, and all treatments did not differ in overall acceptability.     

转谷氨酰胺酶催化对不同大豆蛋白凝胶性的影响

研究转谷氨酰胺酶对大豆分离蛋白和7S、11S球蛋白凝胶特性的影响,采用TA-XT plus物性测定仪、荧光分光光度计对各参数进行测定。结果表明：转谷氨酰胺酶能够显著提高大豆蛋白凝胶的凝胶强度,最佳工艺条件为酶添加量40U/g、温度40℃、pH7.5、作用时间2.5h,但此时凝胶表面疏水性和保水性有所下降。经转谷氨酰胺酶催化后,不同蛋白形成热处理凝胶的凝胶特性均发生显著变化,凝胶强度均显著增加,转谷氨酰胺酶催化后大豆蛋白凝胶强度的顺序为11S＞7S＞SPI。     

超声改性蛋白对玉米淀粉凝胶结构及消化特性的影响

为探究超声改性蛋白对玉米淀粉凝胶结构及消化特性的影响规律,将不同超声时间处理的大豆分离蛋白分别添加至玉米淀粉中,利用傅里叶红外光谱仪、差示扫描量热仪、X-射线衍射仪及流变仪等表征超声改性蛋白与玉米淀粉复配凝胶体系结构,并对其体外消化特性进行分析。结果表明：与原玉米淀粉相比,当淀粉中添加不同超声时间处理的大豆分离蛋白后,玉米淀粉的短程有序性、分子内和分子间氢键强度、糊化焓值(ΔH)均降低,且随着超声时间的延长,呈逐渐降低趋势,当超声时间达到30 min时,复配体系的ΔH降低了27.27%;超声改性蛋白与玉米淀粉间相互作用主要通过疏水作用力;复合凝胶体系的X-射线衍射图显示出典型Ⅴ型结构特征,说明改性蛋白的加入改善了淀粉消化特性,与原淀粉相比,慢消化淀粉和抗性淀粉含量均随着超声时间的延长逐渐升高,慢消化淀粉和抗性淀粉质量分数分别提升了7.01%和3.41%。研究结果旨在为改性蛋白在淀粉基食品中的应用提供理论依据。     

Rheological Characteristics of Fibrinogen-Thrombin Solution and Its Effects on Surimi Gels

Gel enhancing effects of fibrinogen-thrombin on surimi were investigated using failure stress and analyzed by mixture design. Gelation time of fibrinogen-thrombin mixture (20:1) gradually decreased as temperature increased from 5 to 40°C, whereas the G′ and G″ values continued to decrease up to 30°C and then increased at >30°C. Low quality surimi produced higher textural values (stress and strain) when fibrinogen and thrombin mixture (3–5%) had been added. Nonlinear stepwise regression model showed no significant interaction effects between surimi and fibrinogen-thrombin mixture. However, the response trace plot showed that failure stress value of surimi gel was increased by the concentration of fibrinogen-thrombin, but decreased by water content.     

Effect of Surfactant Gels on Dough Rheological Characteristics and Quality of Bread

Sodium stearoyl-2-lactylate (SSL), diacetyl tartaric acid esters of monoglyceride (DATEM), glycerol monostearate (GMS), and distilled glycerol monostearate (DGMS) surfactant gels were made with water and varying shortening contents. The effect of these gels on dough rheological characteristics and quality of bread was investigated. Overall, the surfactant gels improved the farinograph and extensograph characteristics of wheat flour, but the improvement reduced to some extent with the presence of shortening in the gels. Alveograph data indicated that dough properties improved with the addition of surfactant gels. Shortening in gels showed varying influence on the dough alveograph properties of wheat flour. The results indicated that the surfactant gels changed the rapid visco analyzer characteristics of wheat flour, and the presence of shortening in gels further altered the characteristics. All surfactant gels improved the volume, specific volume, texture, and overall quality scores of bread, but the improvement varied for different surfactants. By increasing the addition of shortening in gels, though the quality characteristics further improved, the response to surfactants reduced by increasing shortening content.     

状如琼，凝为脂

在我们喝的饮料粒粒橙中，为什么那些细小的橙子颗粒是悬浮在橙汁中的呢？果冻和布丁为什么是透明，且柔软有弹性的呢？去看看成分表，我们不难发现共同之处，看似不同的食品都添加了一种共同的成分——琼脂。[编者按]     

κ-卡拉胶对大豆分离蛋白乳浊凝胶特性的影响

研究了κ 卡拉胶在不同pH的条件下对大豆分离蛋白乳浊凝胶质构特性和流变特性的影响。研究结果表明 ,pH 7 3条件下的乳浊体系比 pH 6 8的体系更易形成凝胶。卡拉胶质量分数为 0 0 5 %时 ,因与大豆分离蛋白发生静电吸引相互作用形成连接型凝胶而显著提高了凝胶的质构特性和流变特性。 0 2 %时则形成相分离型凝胶 ,降低了凝胶的弹性和内聚性。     

Structural Characteristics of Protein Gels as Determined by an Ultrasound Imaging Technique

Structural density features of gels formed with gelatin, egg albumen, and poultry thigh natural actomyosin were determined with an ultrasound system equipped with a real time monitor, imager and photographic unit. Echo recordings of the acoustic impedance showed that all protein gels were similar in respect to structural density differential patterns. Increases in protein concentration increased the net area occupied by protein junctions and interlinks. The ultrasound imaging technique confirmed the aggregated junction, interlink and interstitial regions that are common features of protein gels.     

Thermoirreversible Characteristics of Curdlan Gels in a Model Reduced Fat Pork Sausage

Dynamic viscoelasticity and thermal characteristics of a model reduced fat pork sausage containing curdlan were investigated. Curdlan formed thermoirreversible gels during preparation of sausage at end point temperatures that were within the range in which such gels usually transform from thermoreversible to thermoirreversible. Dynamic viscoelasticity of curdlan gels and thermal characteristics of curdlan aqueous suspensions were analyzed to help explain the physicochemical behavior of curdlan gels in sausage. Once formed curdlan gels exhibited stronger thermoirreversibility with increasing concentrations. The thermoirreversibility could be attributed to the curdlan concentration being higher than the maximum theoretical curdlan to water ratio.     

大豆分离蛋白凝胶制备和凝胶质构特性研究

本研究以大豆分离蛋白为原料，考察蛋白质浓度、pH值、加热温度、加热时间对凝胶形成的影响，采用物性仪对不同务件下制备的凝胶的质构特性进行研究，不同评价指标得出的结论不尽相同。通过正交实验得出形成凝胶硬度最大的制备条件为：蛋白浓度12％，pH值6．5，加热温度95℃，加热时间35min；形成凝胶脆性最大的制备凝胶争件为：蛋白浓度12％，pH值7．0，加热温度95℃，加热时间25min；形成凝胶弹性最好的制备凝胶务件为：蛋白浓度12％，pH值7．0，加热温度85℃，加热时间35min；形成凝胶粘附性最大的制备凝胶条件为：蛋白浓度12％，pH值7．0，加热温度95℃，加热时间35min。