Rheological Characterization of Grain Legume Pastes and Effect of Hydration Time and Water Level on Apparent Viscosity

An extrusion capillary viscometer was employed to obtain shear stress-shear rate data of two types of cowpea pastes, traditional and experimental. The power law model was found to describe adequately flow behavior of the pastes with consistency coefficients of 77.45 and 59.02, and flow behavior indices of 0.456 and 0.458 for experimental and traditional pastes, respectively. Effect of hydration time (0 - 180 min) and water level (54 - 62%) on the apparent viscosity of experimental paste was determined by extrusion capillary and Brookfield viscometers with correlation coefficient of 0.953. Water level had a significantly greater effect than hydration time on apparent viscosity of cowpea paste.     

Elucidating Factors Affecting Floatation of Fish Ball

ABSTRACT:  Factors affecting floatation of fish ball in water were investigated. The density of threadfin bream (TB) surimi paste significantly decreased ( P < 0.05) as moisture content, temperature, or salt concentration increased. The ability of surimi paste to float or sink in water was observed according to changes in density. In gel texture measurement, when surimi was thawed for 1 h before chopping at 5 °C with 2% salt, the highest breaking force and deformation values were obtained. Apparent viscosity of surimi paste decreased as moisture content increased or salt concentration increased, and chopping temperature decreased. Setting gels in salt solution (5 or 10%) significantly reduced ( P < 0.05) stickiness, which is the tendency to stick to one another.     

Rheological behaviour of wheat flour dough in twin-screw extrusion cooking

A capillary-type viscometer was designed to measure the apparent viscosity of the cooked wheat flour dough on -line in a twin-screw extruder. The effect of mean residence time and specific energy were studied in the ranges 20–45s and 300–800 kJ kkg⁻¹, respectively. A viscosity model was developed which accounts for effects of wall shear rate, moisture content and specific energy. It was shown that the extent of the cooking reaction is largely determined by the specific energy applied.     

Degradation Profiles of Potato Starch Melts Through a Capillary Tube Viscometer

The effects of time‐temperature and strain history on potato starch melts at 150 °C were investigated by use of a capillary tube viscometer. Reciprocating and single extrusions were performed in this study. Shear stress at single extrusion decreased gently as initial heating time increased, while shear stress at reciprocating extrusion decreased rapidly as the number of extrusion strokes increased. A high degree of cold water solubility was obtained by reciprocal extrusion at lower moisture content. From the results of gel filtration it could be concluded that starch molecules were depolymerized by high and reciprocal shear stress. According to these results time‐temperature history was more effective on the depolymerization of starch molecules and degradation of starch granules at higher moisture content, while strain history was more effective at lower moisture content.     

Electrical Properties of Fish Mince During Multi-frequency Ohmic Heating

A multi-frequency ohmic heating system with 30 Hz～1 MHz range which could deliver 250 watts was developed for measuring electrical conductivity and absolute dielectric loss of food samples. Pacific whiting surimi paste and stabilized mince in the 20～70°C range were tested at frequencies from 55 Hz to 200 kHz. Sample impedance decreased slightly with frequency. The DC electrical conductivity (σ_dc) and absolute dielectric loss (ε″) of Pacific whiting surimi paste increased with temperature and salt concentration; adc and ε″ of the stabilized mince increased with temperature. Empirical models of electrical properties for surimi paste (moisture content 79% and salt at 1, 2 or 3%) and stabilized mince (77% moisture and 0.74% salt) were derived. Electrolytic corrosion diminished with frequency.     

Application of an In‐line Viscometer to Determine the Shear Stress of Plasticised Wheat Starch

An in‐line viscometer was designed and constructed to enable determination of the shear stress of plasticised wheat starch during extrusion cooking. The viscometer was installed between the end of the barrel section and the extruder die plate so that the shear stress could be determined for the plasticised material, irrespective of the geometrical shape into which it was subsequently moulded by the extruder die. The extrusion conditions were described in terms of the process parameters, i. e. water content, barrel temperature, screw speed and screw configuration; and of the system parameters, which were the specific mechanical energy input (SME), product temperature (PT) and mean residence time (MRT). The parameters were measured and the results evaluated using statistical methods. Regression equations were used to describe functional relationships between the shear stress and the extrusion conditions on the one hand, and between the shear stress and the product characteristics of the extrudates on the other. The shear stress of plasticised wheat starch determined in‐line can be used to predict the morphological structure (volumetric expansion) and the functional properties (cold paste viscosity and cold water solubility) of extruded, directly expanded starch with a high degree of accuracy. The measurement technique used and the results of the extrusion tests undertaken for this project will therefore enable the shear stress of plasticised material in an extruder to be used as the principle parameter for controlling extruders on‐line.     

LOW-FAT, NO ADDED SALT IN RESTRUCTURED BEEF STEAKS WITH VARIOUS BINDERS

This research investigated technology for the development of a low-fat restructured beef steak devoid of added salt with texture similar to intact muscle. Low-fat (10%), low-sodium restructured beef steaks made from closely trimmed, flaked beef round muscles and tumbled with or without a binding agent were compared to boneless top loin steaks (5–6% fat). Boneless top loin steaks had greater (P < .05) shear resistance, cohesiveness, juiciness, overall desirability, percentage moisture (raw) and percentage protein (cooked) than restructured steaks. Steaks made with 3.0% modified potato starch had slightly more juiciness and moisture content (cooked) and lower expressible fluid content than all other restructured samples. Product made with 1.0% microcrystalline cellulose had lower (P < .05) juiciness scores than top loin steaks and restructured steaks made with no additives or modified potato starch. Use of 0.25% kappa-carrageenan or 1.5% surimi increased (P < .05) sensory scores for off-flavor. Steaks made with 1.5% surimi also had lower (P < .05) sensory scores for overall desirability.     

Electrical Conductivity of Pacific Whiting Surimi Paste during Ohmic Heating

Electrical conductivities of Pacific whiting surimi paste with various moisture contents (75, 78, 81, and 84%) and added salt (1, 2, 3, and 4%) were measured using ohmic heating at alternating current of 3.3, 6.7, and 13.3 V/cm. Electrical conductivity of surimi increased with temperature and salt content and slightly increased with moisture content. Electrical conductivity correlated linearly with temperature (r²= 0.99). Generally, voltage gradient did not affect conductivity. However, variations of conductivity with voltage gradient observed in surimi containing 3–4% salt, were probably caused by electrochemical reactions at electrode surfaces. The empirical model of electrical conductivity predicted values ± 16% of independent experimental results.     

Influence of time-temperature history and strain history on the melt rheology of soy protein isolate at an elevated temperature

Reciprocating extrusion and single extrusion experiments were performed using a completely air-tight capillary extrusion viscometer in order to elucidate the effects of time-temperature history and strain history on the melt rheology of soy protein isolate (SPI) at an elevated temperature (140°C). Both histories produced a decrease in the measured pressure drop during extrusion and these effects were strongly dependent on the sample moisture content. For moisture contents above 41% (dry basis), the time-temperature history effect was predominant more in decreasing the measured pressure drop, whereas the strain history effect was more influential at moisture contents below 30% (d.b.)     

戊二酸木薯淀粉酯的制备及理化性质研究

本文分别制备水相戊二酸木薯淀粉酯(AGAC)和醇相戊二酸木薯淀粉酯(EGAC),使用FT-IR、XRD和SEM进行微观表征,研究两种酯化淀粉的粘度、透明度、流变性、冻融稳定性和抗盐性等理化性质。微观表征的结果显示两种酯化淀粉分子中成功接入了戊二酸基团,两者的晶型均没有发生变化,其整体结构没有受到很大影响,布拉班德粘度仪分析结果表明AGAC的峰值粘度有所提高,同时糊化温度明显降低,EGAC的糊化温度降低,峰值粘度大幅度提高,但粘度稳定性没有提高。AGAC糊液和EGAC糊液的透明度、冻融稳定性和抗剪切力均强于原淀粉,而AGAC和EGAC抗盐性均低于原淀粉,即其热糊稳定性和抗盐性未得到改善。EGAC的透明度高于原淀粉,但低于AGAC;而冻融稳定性、抗剪切能力均略优于AGAC和原木薯淀粉,引入戊二酸基团后,木薯淀粉的透明度、冻融稳定性和抗剪切能力有一定程度的提高。     

RHEOLOGICAL CHARACTERIZATION OF A MODEL FOOD SUSPENSION CONTAINING DISCS USING THREE DIFFERENT GEOMETRIES

The objective of this study was to characterize the flow behavior of a solid-liquid food model which imitates Mexican sauces. The model food suspension consisted of seeds suspended in a shear-thinning fluid (Avicel and Xanthan gum). The effects of size and particle concentration were investigated using a traditional disc geometry in wide gap (spindle), and a ribbon adapted to a rotational viscometer. The effect of particle size was evaluated in a tube viscometer. Power-law parameters and apparent viscosity were estimated in the shear range of each viscometer. The experimental apparent viscosity showed good agreement with predictions obtained using a theoretical expression of relative viscosity for uniform spheres. In all the viscometers investigated, shear-thinning behavior of the suspension was observed, as the aqueous phase, due to low interactions among particles. The ribbon geometry appears to be the best option for flow characterization of food suspensions containing coarse disc shaped particles.     

较低固含量番茄酱的流变性能

用RV—Ⅱ型共轴圆筒旋转粘度仪，研究了一种较低固含量(23％)的番茄酱的流变性能，得出了粘度对切变速率和温度的依赖性。实验表明，番茄酱表观粘度的切变速率依赖性可用幂律模型描述。采用Spencer-Dillon疗程求得体系的零切粘度。用Andrade公式计算的粘流活化能可以表征温度对体系粘度的影响。     

白鲢鱼糜流变特性的研究

本实验利用ARES-RDA流变仪,通过动态振荡测量,研究了不同温度和浓度下的白鲢鱼糜的流变特性、凝胶过程及动态粘弹性的变化规律。结果表明白鲢鱼糜的粘度随剪切速率增大而减小,存在剪切变稀行为;鱼糜的动态剪切模量(包括弹性模量和损耗模量)在5℃和10℃时几乎与动态频率(f)(2～16Hz)无关,其中G’远高于G’’,20℃时,当动态频率(f)>8Hz,糊状鱼糜的动态剪切模量与动态频率有关,随着频率的增加而增加;温度扫描(温度范围:5～70℃)结果表明鱼糜凝胶过程经历了三个阶段:第一段在30℃之前,第二段出现在38～43℃,第三段出现在46℃之后,蛋白开始形成了最终的凝胶。该结果为进一步扩宽白鲢鱼糜的应用范围有一定的借鉴意义。     

COMPARISON OF IN-LINE CONSISTENCY MEASUREMENT OF TOMATO CONCENTRATES USING ULTRASONICS AND CAPILLARY METHODS

This study focuses on the development of a noninvasive, in‐line rheometer using ultrasonics and its comparison with data from a traditional capillary viscometer. The ultrasonic based pointwise viscosity measurement technique combines a measurement of the velocity profile and the pressure drop to determine the shear rate and the shear stress distributions, respectively in a pipe. The experiments were carried out using tomato concentrates at 8.75%, 12.75%, and 17.10% total solids content. The flow system consisted of a 53.2 mm diameter acrylic tube, a positive displacement pump and two pressure transducers. Multiple shear viscosity‐shear rate data were recorded under actual pipeline conditions from a single combined measurement of the velocity profiles using ultrasonics and the pressure gradient, using the pressure transducers. The samples showed shear thinning behavior and a yield stress. Power law and Casson models were used to fit the data and both obtained R² values higher than 0.99. The yield stress was also directly determined from the velocity profiles. Shear viscosity versus shear rate data of the 12.75% total solids sample were obtained by capillary rheometry at four different flow rates. These showed very‐good agreement with those obtained using the velocity profile technique.     

水热参数组合对大豆蛋白-鱼糜共混高水分挤压过程及产品品质的影响

高水分挤压技术是制备具有类似动物肉纤维结构和质地的新型植物基肉制品的前沿热点技术。本实验以大豆分离蛋白（soy protein isolate,SPI）和金线鱼鱼糜为原料（80∶20,m/m）,探究水热参数组合（物料水分质量分数65%、70%、75%,挤压温度125、135、145 ℃）对高水分挤压过程中单位机械能耗（specific mechanical energy,SME）和模口压力的影响,以及对挤出物品质的调控作用。结果表明：在实验所用水热参数组合条件下,高水分挤压过程中,鱼糜凝胶以颗粒形式填充在混合凝胶中,并会影响带有取向性的凝胶结构形成。物料水分质量分数增加的同时提高挤压温度会导致高水分挤压过程中的SME从783.40 kJ/kg显著降低到410.96 kJ/kg（P＜0.05）,模口压力从7.79 MPa显著降低到1.60 MPa（P＜0.05）。水热参数组合作用显著影响SPI-鱼糜混合挤出物的品质,与挤压温度相比,物料水分质量分数影响效果更为显著,当物料水分质量分数为70%、挤压温度为145 ℃时,挤出物组织化程度达到最大（2.36）。多项式拟合结果表明,水热参数组合条件下,高水分挤压过程中的SME和模口压力与SPI-鱼糜混合挤出物硬度、咀嚼度、凝胶强度、持水性和剪切力具有非线性相关关系。本研究可为实现植物蛋白和动物蛋白优势互补、开发动植物蛋白结合的替代蛋白类新产品提供参考和借鉴。     

USING BROOKFIELD DATA AND THE MITSCHKA METHOD TO EVALUATE POWER LAW FOODS

Mitschka proposed a simple technique to calculate average shear stress and average shear rate from data obtained with Brookfield viscometers. It allows for estimation of the apparent viscosity, the flow behavior index, and the consistency coefficient of power law fluids. This method was evaluated for typical shearthinning foods (banana puree, salad dressing, enchilada sauce, and pancake syrup) and found to have excellent potential for quality control testing in the food industry. Results compared favorably with those obtained with a standard cone and plate viscometer.     

A Physicochemical Model for Extrusion of Corn Starch

Corn starch extruded at 32.9, 29.2, 24.5, 22.5, 15.9 and 14.2% moisture was analyzed for expansion ratio, enzyme susceptibility, water solubility index, water absorption index, degree of gelatinization, paste viscosity and heat of gelatinization. A model system based on the combination of raw, gelatinized and dextrinized starch was used to represent the physicochemical properties of the extrudates. Reducing extrusion moisture content resulted in a progressive change from gelatinized-like to dextrinized-like properties. Maximum gelatinization was observed at about 28-29% moisture. Below 20% moisture, dextrinization becomes predominant during high- shear cooking-extrusion. Scanning electron micrographs also validate the assumptions of the model.     

Rheological and Textural Properties of Pacific Whiting Surimi Gels As Influenced by Chicken Plasma

Rheological properties of Pacific whiting surimi, in the absence and presence of chicken plasma (CP) at different levels (0.3–3.0%, w/w), were studied by dynamic rheological (small strain) and torsion fracture measurements, respectively. The surimi paste exhibited two major distinctive rheological transitions during heating (1°C/min) from 20 to 90°C with peaks observed at 33 and 56°C. The abrupt loss of G′ upon heating from 47 to 57°C, and the occurrence of small peak of phase angle at the same temperature range were prevented by the addition of CP. Nevertheless, the final G′ of the surimi paste added with CP was lower than that of the control. But shear fracture stress of both kamaboko and modori gels increased as the CP levels increased and shear strain increased with the addition of CP up to 2% (P < 0.05). CP inhibited the degradation of myosin heavy chains (MHC) caused by endogenous proteinases as indicated by more retained MHC and lowered TCA-soluble peptide content. Whiteness of gels decreased somewhat with increasing CP levels. CP, thus, could be a helpful additive for improving gelling properties of Pacific whiting surimi     

挤压预糊化淀粉的性能及其添加对糙米发糕品质的影响

通过挤压不同水分含量（45%、25%和18%）的大米淀粉制备预糊化大米淀粉,测定其分子量、结晶度、糊化度、水吸收指数、水溶解指数、冷糊黏度等指标,并考察了预糊化淀粉添加对糙米粉糊化特性及糙米发糕品质的影响。结果表明,与原大米淀粉相比,45%、25%和18%水分含量挤压制备的预糊化大米淀粉结晶度分别降低了51.93%、58.93%和59.04%;水吸收指数分别提高了1.56、4.69和6.11倍;水溶解指数分别提高了7.04、16.30和27.64倍;冷糊黏度分别提高了2.00、21.44和14.67倍。挤压还使大米淀粉分子发生降解,产生了更多的小链分子。预糊化大米淀粉性能变化与挤压过程中淀粉的水分含量有关。添加预糊化大米淀粉显著提高了糙米发糕的品质（P<0.05）,高的冷糊黏度和低的分子量（18%水分挤压）更有利于制备比容大（1.64 cm3/g）、孔洞细腻均匀、硬度低（338.59 g）和有弹性的糙米发糕。     

TRIAL METHOD FOR MEASURING THE EFFECT OF LIPIDS ON THE RHEOLOGICAL PROPERTIES OF STARCH PASTE DURING THE GELATION PROCESS

An attempt was made to measure the effect of lipid components on the viscosity and thixotropy of wheat starch paste in a short aging time after gelatinization. Viscometry was used to follow periodically the changes in apparent viscosity (at 76.8 s⁻¹) of the mixed paste of wheat starch and one of a series of lipids in a cone-plate viscometer for 210 min after gelatinization, i.e. a procedure of eight cycles of measurement with a sample. Each cycle of the measurement consisted of viscometry for 3 min and a rest period for 27 min at 30°C. The apparent viscosity of all the samples decreased greatly during the 3 min measurement due to thixotropic breakdown of the macroscopic structure in the samples. The results suggest that the presence of a small amount of free fatty acid and monoglyceride may play a role in reducing starch paste gelation.