人造板在压缩载荷下的粘弹性研究及其意义

粘弹性是人造板的重要特性,直接影响饰面人造板的物理力学性能。在总结近几年的有关研究基础上,讨论了人造板粘弹性与饰面板性能的关系。     

鸡蛋贮藏期蛋白粘弹性变化

用双毛细管法测量了鸡蛋蛋白沿蛋形截面短轴各点粘弹性参数的分布及其分布随贮藏时间的变化情况。结果表明,在贮藏期内各部稠蛋白稀化过程不同,内侧稠蛋白稀化较快,外侧稠蛋白稀化较慢,随贮藏期延长,两者趋于一致。     

Molecular aspects of cereal β-glucan functionality: Physical properties,technological applications and physiological effects

Cereals β-glucans are linear homopolysaccharides of consecutively linked (1→4)-β-d-glucosyl residues (i.e. oligomeric cellulose segments) that are separated by single (1→3)-linkages. β-Glucans display all the functional properties of viscous and gel forming food hydrocolloids combined with all the physiological properties of dietary fibres. This review focuses on the relationships between the molecular–structural characteristics of β-glucans and their physicochemical properties in aqueous dispersions and in food systems as well as their physiological functions in the gastro-intestinal tract. The physical properties of β-glucans, such as solubility and rheological behaviour in the solution and gel states, are controlled by their molecular features, such as their distribution of cellulosic oligomers, their linkage pattern and their molecular weight as well as by temperature and concentration. The technological and nutritional functionality of β-glucans is often related to their rheological behaviour. Incorporation of β-glucans into various products (bread, muffins, pasta, noodles, salad dressings, beverages, soups, reduced-fat dairy and meat products) showed that attributes, such as breadmaking performance, water binding and emulsion stabilising capacity, thickening ability, texture, and appearance appear to be related to the concentration, molecular weight and structure of the polysaccharide. The health benefits of β-glucans, such as reducing blood serum cholesterol and regulating blood glucose levels, are also correlated with the amount and molecular weight of the solubilised β-glucans in the gastro-intestinal tract.     

薇菜压缩应力松弛与蠕变力学特性研究

通过研究野生富硒植物薇菜茎的压缩应力松弛、蠕变粘弹性力学行为,可为绿色食品的物性学研究提供粘弹性力学性质数据。以吉林省汪清县野生薇菜茎为研究对象,进行压缩应力松弛、蠕变试验,得到薇菜茎应力松弛、蠕变数据和曲线,以及归一化应力松弛函数、蠕变函数曲线和应力、应变随时间变化的规律,表明薇菜具有良好的压缩粘弹性力学性质,属粘弹性材料。     

加工番茄粘稠度与其他农艺性状的相关与通径分析

通过对加工番茄28个品种或杂交组合的主要农艺性状相关及通径分析,估测了番茄10个主要性状对粘稠度形成影响的相对重要性。结果表明:番茄果胶含量和干物质含量与粘稠度呈极显著正相关,对粘稠度的直接效应最大,是影响粘稠度的主要因素,在加工番茄高效育种中果胶含量和干物质含量可作为主要选择性状。     

A simple approach to predicting dough sheeting thickness

The prediction of final sheet thickness after rolling of wheat flour dough is studied using an approximate method that concentrates on the initial, intermediate and final material configurations. A newly proposed viscoelastic constitutive model containing a damage function is used. Compressibility and sideways spreading are ignored. Predictions of final sheet thickness given roll speed and diameter, gap and initial thickness data, show excellent agreement with available experiments on unyeasted dough, in contrast to many previous attempts.     

Three dimensional simulation of viscoelastic polymer melts flow in a cast film process

Three-dimensional simulation of the cast film process for viscoelastic polymer materials was carried out using the finite element method. The flow between the extrusion die and chill roll was assumed to be steady-state and isothermal and the rheological property of material was characterized by a single-mode PTT model. Gravity and inertial flow were considered in the simulation work, but neglecting die swell at the die exit, surface tension, crystallization, transient disturbance and film sag. Simulation results of the cast film production line were compared with the experimental data on the velocity profiles and neck-in values. Neck-in and edge bead was well predicted and the influence of strain-hardening nature, elasticity of materials and operation conditions on the final film shape was also investigated. It was found that the effect of strain-hardening nature was masked for the material with a very low relaxation time when the single-mode PTT model was adopted. Greater elasticity helped to produce a film with smaller neck-in and less waste edge. When the air gap length was increased, it was predicted that neck-in phenomenon would be promoted as well. Moreover, it was found that ratio of neck-in values under different air gap lengths was approximately equal to that of air gap lengths, which was consistent with experimental evidence.     

Impact of different isolation procedures on the functionality of zein and kafirin

Commercial corn prolamin (zein) aggregates in water at elevated temperatures into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production of gluten-free bread from true dough systems and not from batters. The present study examined laboratory-scale isolation of such functional zein from dry milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure α-zeins, with a maximum ratio of (β + γ)/α-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (β + γ)/α-zeins. Isolation of the analogous prolamin (kafirin) from dry milled sorghum required a more hydrophobic extractant such as 83% isopropanol to achieve partial functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added; however, it quickly became firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide bonds are the key to gluten-like functionality of zein and kafirin.     

高压处理蛋黄酱动态粘弹特性的研究

使用AR－500流变仪测定了不同压力处理后的蛋黄酱动态粘弹特性，得到复模量、复柔度、复粘度和贮能模量的变化曲线。结果表明，高压处理后的蛋黄酱是剪切稀化流体。应用动态粘弹特性理论对试验结果进行了分析，初步证实高压对蛋黄酱中的蛋白质分子存在一定的解聚和伸展作用。     

Viscoelastic properties of tablets from Osborne solubility fraction,pentosans, flour and bread using relaxation tests

There is no previously published data covering the viscoelasticity of Osborne protein solubility fractions. Therefore, the objective of this study was to compare the viscoelastic properties of Osborne fractions, water soluble pentosans, flour and bread using relaxation tests. Sintered tablets from glutenins presented similar elasticity as gliadins but almost twice the viscosity. However, most of the wheat viscoelasticity performance in tablets was given by the sum of the non-gluten components (albumins, globulins, residue and especially water soluble pentosans). The residue was 86.1% w/w in flour and contained 4% protein while its estimated viscoelastic effect was higher compared to all the other flour components. Regarding the estimated viscosity in flour due to protein from specific fractions, it was higher in gliadins compared to glutenins. The residue although has low protein in flour (4.0%), the large amount of residue in flour had significant viscoelastic effect. The viscoelasticity of water soluble pentosans corrected by weight was similar to the Osborne protein fractions. The results indicate that the starch, pentosans, and non-gluten components may not be considered merely as inert filler and play a major role in determining the viscoelastic nature of flour and bread.