Steady state flow behaviours of extruded blend of rice flour and soy protein concentrate

Rheological properties in terms of steady state flow behaviours of extruded dispersions (rice flour/soy protein concentrate blend), were investigated using dynamic rheometry. The effects of concentration (2%, 5%, 7%, 9% and 11%) and temperature (25–70 °C) on the rheological parameters (yield stress, flow behaviour index) of the non-expanded pellet blend (12.5% protein) were determined using common rheological models. Steady-shear viscosities in a range of shear rate from 0 to 500 s⁻¹ were observed as a function of concentration and temperature. From typical curves showing the dependence of shear stress on shear rate, it could be observed that all suspensions exhibited a non-Newtonian and pseudoplastic behaviour. The model that best fitted the experimental data at all temperatures and concentrations was the Herschel–Bulkley model.     

冷榨亚麻籽油的流变特性研究

通过低温压榨亚麻籽获得冷榨亚麻籽油（cold—pressed flaxseed oil,CFO）,并分析其主要理化指标,着重研究CFO的静态、动态流变特性,同时分别采用Casson、Herschel-Bulkley和Bingham模型对其流体行为进行拟合,并采用Arrhenius方程分析其粘度热动力学参数。研究结果表明：在剪切速率为0．1～200s“下,CFO由非牛顿流体逐渐转化为牛顿流体;当剪切速率大于10s^-1时,CFO呈牛顿流体;同时分析得出CFO的粘度活化能为3095．4cal／mol;CFO的粘度、剪切应力、损耗模量、塑性稠度系数、高剪切极限粘度和稠度系数随着温度升高而降低,但是温度变化对CFO的贮能模量影响不显著;另外通过比较3个流变模型得出Bingham模型适用于CFO。     

Comparative Study on Functional,Rheological, Thermal,and Morphological Properties of Native and Modified Cereal Flours

Effect of extrusion on the functional, rheological, thermal, and morphological properties of the modified cereal flours from different cereals was assessed. Rice flour, wheat flour, and flour, in combination (rice: wheat, 50:50) were passed through twin screw extruder to obtain modified cereal flours at variable conditions (barrel temperature: 175 and 190°C, feed moisture: 14 and 16% and screw speed: 500 rpm). Functional properties (water absorption index, water solubility index, swelling index, and viscosity) improved in modified cereal flours as compared to the unmodified flours. Modified flours showed lower paste viscosity as compared to unmodified flours, which was a desirable property for modified flours to be utilized as a functionality ingredient in food products. Processed flours recorded higher onset (T_o), peak (T_p), and endset (T_e) temperature and showed higher enthalpy change (?H) than the raw cereal flours. Degree of gelatinization was higher in flours processed at higher barrel temperature and feed moisture. The morphological pattern of modified flours was determined by scanning electron microscopy. The starch surface of cereal flours (modified and unmodified) differed from each other with respect to their morphological pattern.     

Rheological and functional properties of flours from banana pulp and peel

Unripe banana flour can be an alternative to minimize post‐harvest loss and to increase the aggregate value of banana fruit. Flour from unripe banana is rich in phytosterols and resistant starch, being proposed as health food. Flours from unripe banana peel and pulp were evaluated on their composition, phytosterols content, thermal and rheological properties, and pasting profiles. High amounts of β‐sitosterol, campesterol, and stigmasterol were found in flour from banana peel. These samples showed lower viscosity values of pasting profiles, lower energy enthalpy on gelatinization, and higher temperature of gelatinization than those ones from pulp. Anti‐oxidant treatment of fruits with citric acid does not change pasting profiles of flours from pulp, but resulted in slight increase in viscosity, suggesting that structure of starch could be modified by acidification.     

Sensorial and biological evaluation of an extruded product made from corn supplemented with soybean and safflower pastes

A puffed product was made by extruding corn flour supplemented with soybean and safflower pastes. Mixes with the following proportions of corn flour, soybean and safflower pastes: (i) 89:8:3, (ii) 83:11:6 and (iii) 80:17:3 were extruded. The corn flour, soybean and safflower pastes used had 6.6%, 45.9% and 32.9% protein content respectively. In addition, the soybean paste contained 11.78 units of inhibited trypsin/mg of sample, which means it was appropriate for human consumption. Sensory evaluation of extruded products showed that there were no significant differences in flavour, crunchiness and acceptance in the case of products 1 and 3, when compared with samples made from corn flour alone. Product 2 had lower scores, as it had a bitter taste because of the greater amount of safflower paste used. Biological testing showed that all the products containing soybean and safflower pastes were superior to the 100% corn diet in terms of food conversion, growth rate and weight gain.     

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.     

Rheological properties of cereal starch gels and Mesona Blumes gum mixtures

The effect of Mesona Blumes gum (MBG) was examined on steady and dynamic shear of MBG/rice starch and MBG/wheat starch gels. In addition, stress relaxation and creep tests were performed for two types of cereal starch gels. The flow curves of both MBG/starch gels exhibited pseudoplastic behavior at shear rates between 0.01 and 10 s⁻¹, and the data were fitted into the power law model (R² = 0.91–0.98). Dynamic mechanical spectrum showed that all gels were strong gels in frequency between 0.1 and 10 Hz. Stress relaxation data at different strains indicated a strain‐softening phenomenon for both gels. Data were fitted into Maxwell model (R² = 0.91–0.98). Creep curves were conducted at the shear stress 6.4 Pa within linear viscoelastic region of both MBG/starch gels. Data were fitted into Burgers model (R² = 0.91–0.98). Apparent viscosity η, storage moduli G′, equilibrium stress relaxation modulus G_e and zero apparent viscosity η₀ of MBG/rice starch gels decreased in the following order: 6/0>6/0.5>6/0.35>6/0.1 (starch/gum w/w). Whereas η, G′, G_e, and η₀ of MBG/wheat starch gels increased gradually along side the increase of MBG contents. The stress relaxation time λ of MBG/rice starch gels increased in the following order: 6/0<6/0.5<6/0.35<6/0.1 (starch/gum w/w) while λ of MBG/wheat starch gels decreased gradually with the increase of MBG level. The influence of MBG on two examined cereal starch is totally opposite.     

System parameters and product properties response of soybean protein extruded at wide moisture range

In order to explore the effect of water during extrusion process, soybean protein isolate (SPI) was extruded using a pilot-scale twin-screw extruder at 28%, 36%, 44%, 52% and 60% moisture content and 140, 150 and 160 °C cooking temperature. The extrusion system parameters like in-line viscosity at die, mean residence time and specific mechanical energy (SME), product textural properties including tensile strength, hardness, chewiness and degree of texturization, and the molecular weight distribution characterized by SDS–PAGE were investigated. And the interrelationship between system parameters and product properties were analyzed. The results showed that moisture content was a more important factor on system parameters and product properties than cooking temperature. Higher moisture content resulted in lower viscosity of dough in the extruder, shorter residence time and lower conversion ratio of extruder mechanical energy into heat energy, finally reducing significantly the tensile strength, hardness, chewiness and the degree of aggregation. The data from extrusion system parameters and product properties correlate well and could be used to explain and control the characteristics of extrudate.     

Rheological properties of xanthan gum-gelatine spray-dried mixtures. Application in a custard-like formulation

 The effect of a spray-drying process on the rheological and textural properties of xanthan gum-gelatine dispersions was studied. Remarkable differences were found between co-dried samples and dispersion samples. Apparent viscosity and extrusion values were higher and shear-thinning behavior more pronounced than in non-dried samples. Also, stronger thickening and stabilizing properties were noticed. With regard to viscoelastic properties, an increase in the elastic component was observed. The new product was used in a standard confectioner's custard formulation and its properties were studied. When these samples were compared with a traditional custard made with starch, although enhanced rheological properties were recorded a similar visual appearance between samples was observed. Received: 27 March 2000     

Rheological properties of pectin-enriched products isolated from butternut (Cucurbita moschata Duch ex Poiret)

Rheological behavior of five different pectin-enriched products obtained from a cell wall enriched powder of butternut (Cucurbita moschata Duch ex Poiret) was evaluated through flow and oscillatory assays. The product SE was obtained through treatment with citrate buffer; C1 and C2 were obtained using cellulase and different enzyme-substrate ratios while H1 and H2 resulted from hemicellulase treatment at different levels. SE- and H1-pectin-enriched fractions showed the best performance as thickeners as indicated by their highest Newtonian viscosities and time constants on shear-thinning along the flow. These fractions showed a structure with the highest density of interactions between the hydrated macromolecules when solutions were evaluated at rest. Fractions obtained with a higher activity of hemicellulase (H2) or with the lowest activity of cellulase assayed (C1) showed the same degree of structure when evaluated at rest, while C2-fraction presented the lowest density of macromolecular interactions in water, behaving as a diluted hydrocolloid solution as confirmed by its fitting to the Cox-Merz rule. Molecular weight distribution of polysaccharide fractions along with chemical composition helped to explain the rheological behavior of these isolated fractions which contained between 39 and 78 g of galacturonic acid per 100 g of product. With the exception of C2 fraction, pectin-enriched products isolated from butternut showed an interesting range of thickening properties and can be used as thickeners in the food industry.     

鸡骨明胶的流变性研究

研究从鸡骨中提取的明胶的流变性质。结果表明：质量分数为0．5％的鸡骨明胶溶液为塑性流体，其流动需要克服一定的屈服应力，屈服应力的大小受温度影响，温度越高，屈服应力越小；当剪切应力大于屈服应力时，粘度基本不随剪切速率变化，表现出牛顿流体的流动特征；温度越高，鸡骨明胶溶液粘度越小，温度对其的影响符合Arrhenius模型，流动活化能为19．58kJ／mol；鸡骨明胶的粘度随质量分数的增加呈指数递增；鸡骨明胶的粘度受pH值影响，在等电点9附近，鸡骨明胶溶液的粘度最小，偏离pI则粘度增大；鸡骨明胶的粘弹性强烈受温度的影响，质量分数为3％的鸡骨明胶从粘性为主的溶胶体系变成以弹性为主的凝胶体系的转变温度(胶凝点)为23．6℃，而凝胶转变成溶液的转变温度(溶点)为33．6℃。适当质量分数及在室温条件下，鸡骨明胶主要表现为弹性体。     

大豆膳食纤维对面团流变性质的影响

将豆腐生产的下脚料豆渣在挤压前后添加到面粉中，对面粉粉质和面团拉伸性质所受影响进行了研究。     

番茄浆料的流变特性研究

对不同浓度(15、18、20和24°Brix)的番茄浆料分别在30、40、50和60℃时的流变学性质进行了研究。结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40-140pa)。通过回归分析,发现数学模型,K=koexp(Ea/RT)和K=Aexp(BC),可以分别用来描述温度和浓度对番茄浆料稠度系数的影响。在实验条件下,实验值能够很好地拟合模型。并且推导出温度和浓度同时对番茄浆粘度影响的方程。利用这些方程,可以预测实际加工中不同温度和不同浓度下番茄浆料的粘度。     

梨果实蠕变基本流变特性研究

应用TA-XT2i质地分析仪对梨果实进行蠕变测试,结果表明,蠕变试验条件对蠕变变形量的影响是载荷大于蠕变时间,载荷越大,蠕变时间越长,蠕变变形量越大,越容易发生损伤.     

Effect of wheat bran on the mechanical properties of extruded starchy foams

Incorporation of wheat bran has a significant effect on the texture of extruded starchy products. This can be explained by changes in the mechanical parameters of the products. The stress at rupture and elastic modulus of wheat flour-based solid foams, obtained at different extrusion conditions and bran concentration, were measured using a three-point bending test. Both parameters were positively correlated with the foam relative density according to the Gibson–Ashby model. At same relative densities and bran concentration, finer structures with higher density of small cells led to a higher mechanical strength of the foams. The stress at rupture of the unexpanded material was decreased when increasing the bran concentration. Nevertheless, expanded foams with added bran at an intermediate level showed increased mechanical strength. This was attributed to the finer cellular structures obtained. The effect of increasing the bran to a higher concentration on the mechanical properties was depending on the cell wall thickness and bran particle dimensions. At high relative density, the strength of the foams was further increased due to the even finer structures obtained. At low relative density, even though finer structures were also obtained, the stress at rupture of the foams was decreased. This may be explained by the lower cell wall thicknesses and low adhesion properties between bran and starch favoring rupture of the cell walls.     

梨膏的流变学特性及其影响因素

目的 考察人为加糖、加胶后梨膏触变性及黏度的变化。方法 以鸭梨为实验材料,通过真空浓缩方式制备鸭梨膏,采用HR-10型流变仪对其流体类型、黏度、触变性进行测定。结果 鸭梨膏属于非牛顿流体,具体细分为无限接近牛顿流体的假塑性流体,具有剪切稀化特性和正触变特性;损耗模量G″总是大于储能模量G’,表现出液体黏性性质;剪切速率与剪切力变化关系符合PowerLaw方程,拟合效果良好(r2>0.99);温度显著影响梨膏黏度,黏度随温度升高而降低,二者关系符合Arrhenius方程,拟合效果良好(r2>0.99);可溶性固形物含量(solublesolidscontent,SSC)对黏度的影响符合指数函数关系,模型拟合效果良好(r2>0.99);SSC以及人为加糖、加胶处理对梨膏触变性、黏度影响显著(P<0.05),黏度随SSC的升高而增强,人为加胶、加糖加胶会导致梨膏黏度显著升高(P<0.05);触变性随SSC的升高而增强,同时人为加糖、加胶、加糖加胶处理会导致梨膏触变性显著减弱(P<0.05)。结论 人为添加糖、胶会导致梨膏的流变学特性发生改变。本研究可为工业...     

Rheological equation of state for shear-thickening food systems

A modified equation of state was developed for shear-thickening systems. The model was applied for describing the rheological properties of various starch pastes for describing the rheological properties of various starch pastes and pastes with hydrocolloids addition. The parameters of the model were estimated using the Tikhonov regularisation method. In order to compare the results, some other models were also fitted to the experimental data.     

Rheological properties of reduced lactose whey dispersions

The rheological behaviour of reduced lactose whey (RLW) dispersions of several different types of whey products was investigated with dynamic small amplitude oscillatory (SAOS) rheometry and rotational rheometry. The different aggregation states of the proteins were measured by using size-exclusion chromatography (SEC) with multiangle laser light scattering (MALLS). Differences in the mineral content (especially calcium and phosphate) of the RLW samples contributed to their different rheological properties. Calcium phosphate/whey protein aggregates were probably formed when the mineral content increased, resulting in an increase in the size of the aggregates and higher viscosity. These complexes were also more sensitive to heating.     

Effect of homogenization conditions on physicochemical properties of chitosan-based film-forming dispersions and films

Film-forming dispersions (FFD) based on high molecular weight chitosan (CH) alone or in combination with oleic acid (OA) were prepared under different homogenization conditions (rotor-stator or rotor stator together with microfluidization at different pressures). Film-forming dispersions (FFD) were characterized in terms of particle size distribution, rheological properties, distribution and ζ-potential. In order to study the impact of the properties of the FFD on the casted films, the water vapour permeability, mechanical properties and microstructure of the dry films were evaluated. Results showed that microfluidization promoted significant changes in the size and surface charge of the FFD particles, which in turn had an impact on the rheological properties of the FFD. The changes were more marked with the increase in microfluidization pressure. As regards film properties, the higher the microfluidization pressure in the FFD, the lower the water vapour permeability values and the stiffer the CH-OA composite films. These results were explained by film microstructure, which was observed by SEM.