Relation Between Particle Properties and Rheological Characteristics of Carrot-derived Suspensions

The effect of particle properties on the rheological behaviour of carrot-derived suspensions was investigated systematically. Hereto, a range of relatively monodisperse suspensions, with varying average particle sizes (～73, 176, 262 and 369 μm) and pulp contents (from 30 to 65 wt.%), was prepared by the reconstitution of carrot tissue particles in water. Suspensions with average particle size of ～73 μm consisted of cell fragments, whereas suspensions with larger particle sizes contained mainly cell clusters of which the cell number increased with increasing particle size. The rheological characteristics showed that the carrot-derived suspensions have a non-Newtonian behaviour with a yield stress, depending on particle concentration, size and type. The network structure of all suspensions could be described as a weak gel. Increase in yield stress and storage modulus with particle concentration could be fitted to a power law model. A unique linear relation was found between the yield stress and the plateau modulus, independent of the particle size and type. Particle concentration, size and type appeared to be key structural parameters controlling the rheology of these carrot-derived suspensions. When comparing the rheological behaviour of the reconstituted suspensions with the original carrot purée of similar average diameter and pulp content, the network structure (measured as yield stress or storage modulus) in carrot purée was weaker, which may be attributed to the broader particle size distribution.     

Velocity Distributions of Food Particle Suspensions In Holding Tube Flow: Distribution Characteristics and Fastest-Particle Velocities

Velocity distributions of model food particles were investigated by videotaping particles suspended in sodium carboxymethylcellulose (CMC) solutions during passage through a transparent holding tube similar in dimension to that of commercial aseptic processing systems. The distributions could be well described by log-normal models. Fastest particle velocities were below theoretical centerline velocities for Newtonian fluids but were above theoretical values for the fluids used. Results indicated that for particle concentration levels used in these studies, channeling and particle-fluid interaction effects may be significant.     

Velocity Distributions of Food Particle Suspensions in Holding Tube Flow: Experimental and Modeling Studies on Average Particle Velocities

Average particle velocities of model food particles were investigated by videotaping particles suspended in sodium carboxymethylcellulose solutions during passage through a transparent holding tube similar in dimension to that of commercial aseptic processing systems. Results indicated the mean normalized velocity of particles was significantly affected by particle Froude number and a dimensionless viscosity. Within the range of this study, particle concentration effects were significant only with respect to standard deviations of distributions. Generalized Reynolds number poorly correlated with mean normalized particle velocity. A mathematical model for particle action was in qualitative agreement with experimental results.     

Dietary Fiber and Fecal Characteristics in Rats: Effects of Level and Particle Size of Bran

Particle size and levels of dietary wheat brans were compared in regard to their effects on various fecal characteristics in rats. Particle size appeared to have no effect on fecal moisture. When compared with a 15% medium bran diet, a 15% fine bran diet decreased wet weight (−9%, P < 0.01) and volume (−18%, P < 0.01), and increased density (+14%, P < 0.01) of feces. A 15% coarse bran diet induced a low fecal density (0.839), which is a desirable effect. Density decreased when the level of bran of the same particle size was increased. However, a 25% fine bran diet still induced higher (P < 0.05) density than a 15% coarse bran diet, stressing the importance of bran coarseness on fecal density.     

Corn Grits Particle Size and Distribution Effects on the Characteristics of Expanded Extrudates

The effects of corn particle size and distribution on the ex trusion-cooking process was studied. Extrusion cooking was carried out in a twin-screw corotating extruder. The effects of particle characteristics were studied by analyzing process responses on-line, by expansion indices, mechanical (puncture test) and structural (computerized image analysis) prop erties of the extrudate. An increase in particle size for a given biochemical composition gave extrudates that were harder, with a modified expansion and lower cell density. The par ticle size distribution in the range studied was not significant. Correlations were found between expansion indices and process responses.     

纸张涂料流变性的检测及影响因素

介绍了影响涂料流变性的各种主要因素,重点论述了几种主要颜料的流变性能以及颜料、胶粘剂和辅助胶粘剂对涂料流变性的影响。最后介绍了涂料流变学未来的研究方向,为涂料流变性的研究提供参考。     

Mangosteen Oil-In-Water Emulsions: Rheology, Creaming, and Microstructural Characteristics during Storage

The rheological properties and physical stability of mangosteen (Garcinia mangostana L.) extract in oil-in-water (MIO/W) emulsions were investigated. Rheological study on the emulsions exhibited Newtonian flow behavior. The 20?wt.% emulsion showed higher apparent viscosity than 10?wt.% MIO/W sample. The effects of salt (NaCl) concentration (0, 50, 100, and 200?mM) and heat treatment (70?°C) on the stability of the emulsions were also examined. Heat (70?°C)- and NaCl (100 and 200?mM)-treated emulsions showed creaming and droplet aggregation on storage for a period of 60?days. The 10?wt.% MIO/W emulsions stored at 4?°C showed a homogeneous distribution of oil droplets with good stability to creaming and viscosity independent of shear stress (i.e., a Newtonian liquid).     

二氧化钛对涂料流变性的影响

颜料是涂料的重要组成部分,影响到涂料的流变特性和产品质量。金红石型二氧化钛折射系数高、白度高和化学稳定性好,能提高纸张不透明度和涂层遮盖性。本文以金红石型二氧化钛部分取代瓷土,研究了其对涂料流变性和涂布纸光学性能的影响。研究发现：随着涂料配方中二氧化钛用量的增加,涂料的低剪切黏度和高剪切黏度增加,导致涂料高剪切力条件下的流变性变差。二氧化钛对涂料保水性影响不大。二氧化钛会吸收紫外光,降低了荧光增白剂的应用效果;但能增加成纸的不透明度。     

Emulsified Milkfat Effects on Rheology of Acid-Induced Milk Gels

Reconstituted skim milk formed by a gel by acidification to < pH 5.2 and heating to 60°C. The gel compressive stress (σ_c) was influenced by the heating process, increased with milk-nonfat-solids (MNFS) and reached a maximum at pH 4.0. The addition of emulsified fat facilitated gelation, increase gel σ_c and shear modulus, and decreased gel deformability. At an equal fat concentration, emulsions containing small-sized fat globules (i.e., more globules) reinforced the gels more markedly than emulsions comprised of large globules reflecting the importance of number of globules in the gels. Electron micrographs revealed crosslinkages between fat globules and casein particles in the gel network, which may have caused reinforcement of milk gels by milkfat.     

Quality Indicators of Rice-Based Gluten-Free Bread-Like Products: Relationships Between Dough Rheology and Quality Characteristics

The design of gluten-free bread-like products involves the study of gluten-free dough rheology and the resulting baked product characteristics, but little information has been obtained connecting dough and baked product properties. The aim of this study was to determine quality predictors of gluten-free bread-like products at dough level by defining possible correlations between dough rheological properties and both instrumental parameters and sensory characteristics of those products. Diverse rice-based gluten-free doughs were defined and rheologically characterised at dough level, and the technological and sensorial quality of the resulting baked products was investigated. Dough Mixolab® parameters, bread-like quality parameters (moisture content, specific volume, water activity, colour and crumb texture) and chemical composition significantly (P?<?0.05) discriminated between the samples tested. In general, the highest correlation coefficients (r?>?0.70) were found when quality instrumental parameters of the baked products were correlated with the dough Mixolab® parameters, and lower correlation coefficients (r?<?0.70) were found when sensory characteristics were correlated with dough rheology or instrumental parameters. Dough consistency during mixing (C1), amplitude and dough consistency after cooling (C5) would be useful predictors of crumb hardness; and C5 would be also a predictor of perceived hardness of gluten-free bread-like products.     

Relation Between Oxygen-17 NMR and Rheological Characteristics of Wheat Flour Suspensions

Water binding has a significant influence on the rheological properties of wheat flour suspensions. Wheat flour-water suspensions at concentrations from 60 - 95% wet basis were subjected to rheological and NMR analyses in order to ascertain the relation between the two methods. The rheological data obtained by the Haake RV-3 Rotoviscometer followed the Power Law, thus comparisons were based on consistency coefficient (a) and flow behavior (b) values. The NMR spectrometer measured oxygen-17 relaxation rates (34 MHz in water and in deuterium oxide) as an indication of water mobility. The data showed a general inverse relationship between consistency coefficient and water mobility. However, the data indicated three distinct regions, each showing a linear relation with water mobility decreasing as apparent viscosity increased.     

水溶性米糠多糖的溶液流变学性能研究

以脱脂米糠为原料,提取、分离水溶性米糠多糖,以动态流变仪为主要实验仪器,研究了水溶性米糠多糖的流体力学性能和相关影响因素.研究结果表明,水溶性米糠多糖溶液是典型的非牛顿流体,表现为剪切稀化的流体性能,多糖浓度越高,溶液剪切稀化现象越严重.同时其多糖溶液的流体性能还受体系温度、剪切速率和pH值等因素的影响.     

Hydrocolloids and Rheology: Regulation of Visco-elastic Characteristics of Waxy Rice Starch in Mixtures with Galactomannans

Texture and sensory properties of starch solutions or gels, resp., can be influenced by regulating the visco-elastic properties that cannot be adjusted by simply varying the waxy rice starch concentration. Therefore, the hydrocolloid galactomannans guar gum and locust bean gum were used for addition. A total polymer concentration of c = 5% was maintained through all tests, the hydrocolloid fractions varied (c_HK = 0.5%, 1%, 2%). The mixtures were entirely decomposed in an autoclave at 130°C resulting in an almost complete destruction of the granular starch structure. With rheomechanical oscillation measurements in the linear-visco-elastic range the influence of the galactomannans onto viscosity yield and visco-elasticity was determined quantitatively. It was found that the influence on the viscosity is depending on the deformation rate. At low frequencies and with increasing galactomannan fraction the viscosity decreases, while above a critical frequency ω_kr an increase in viscosity could be detected compared to pure starch. The mixtures also displayed an increase in viscous fractions versus elastic fractions compared to pure starch. With increasing galactomannan fraction, the ratio storage modulus/loss modulus is reduced continuously from G′:G″ > 10 (definitely mainly elastic) to G′:G″ = 1 with simultaneously decreasing influence of the frequency. Based on the presented data and knowledge on solution structure of the individual components, a model for describing network structures in mixtures was developed. Changes in viscous-elastic properties are based on a thermodynamic incompatibility between starch and galactomannan fractions. The mixtures contain mixed network structures, with waxy rice starch (permanent network points) and galactomannans (temporary network points) contributing individually and characteristically to the resulting flow behaviour.     

Particle Size Characteristics of Ground Soy and Red Gram

Grinding characteristics of soy and red gram were compared employing single- and two-stage grinding in a mixer grinder. The initial size as well as hardness of soy (?216 N) and red gram (?220 N) were nearly equal. However, final particle size of red gram (61 μm) was much lower than soy (255 μm), indicating that red gram was relatively easier to grind. Analysis of microstructure indicated that typical internal structure and intercellular forces could play a significant role in determining the grinding characteristics of individual grains. With the same amount of energy input (200 kJ/kg), size reduction ratio in soy increased from 12 to 16 during two-stage grinding. Energy and particle analyses revealed that a two-stage segregated grinding is suitable for soy while a single-stage grinding is adequate for red gram. Classical dry grinding laws were applicable after initial break up suggesting their suitability for secondary grinding of soy and red gram.     

Coating Behavior of Suspensions

The ability of a solid suspension in liquid medium to coat a vertical surface was analyzed. Results with model suspensions, consisting of polystyrene particles (37–147 μm) in volume concentration from 15–40%, show that coating thickness increases linearly with particle concentration in suspension, and then increases sharply at a critical concentration. The coating thickness of sucrose in corn oil shows behavior similar to that of the model system.     

Pectin and Raspberry Concentrate Effects on the Rheology of Stirred Commercial Yogurt

The influence of pectin (0.0–0.5%) and raspberry concentrate (64°B; 0–10%) on the rheological characteristics of commercial stirred yogurt was evaluated using a computer-controlled rotational viscometer. All upward flow curves (shear rate vs shear stress) followed the Herschel-Bulkley model while downward curves showed a linear relationship. The consistency coefficient (upward flow) and apparent viscosity (downward flow) showed a continuously increasing trend with increasing pectin and raspberry concentrate. The rheology of flavored yogurt could be fabricated by post-incubation mixing of stirred yogurt with pectin and raspberry concentrate.     

Rheology of mozzarella cheese: Extrusion and rolling

A capillary rheometer was used to determine the processability and rheology of mozzarella cheese over the temperature range of 25–60 °C. End pressure corrections, which are corrections associated with the entry and exit of the mozzarella cheese in and out of the capillary die, were found to be significant. Surprisingly, wall slip was found to be insignificant up to shear stress values of 30 kPa. Capillary extrusion at low temperatures (<50 °C) resulted in extrudates that were distorted, while at higher temperatures (>50 °C), the extrudates were fairly smooth. Rolling experiments at 25 °C indicated that rolling can be used to shape mozzarella cheese (at a reduction ratio <2.1) without fracturing. Based on the extrusion and rolling experiments, mozzarella cheese can be described as a power law fluid with an index of about 0.24, while at higher temperatures (30 °C<T<60 °C), the power law index is about 0.4, indicating its increased flowability.     

浓缩葡萄汁在红花籽油贮藏中的抗氧化效果

通过测定木纳格、无核白、美国红提、玫瑰香四种浓缩葡萄汁的清除DPPH·能力,评价了四种葡萄汁的抗氧化能力。同时研究了四种浓缩葡萄汁在红花籽油贮藏中的抗氧化效果。结果表明:四种浓缩葡萄汁的抗氧化能力强弱顺序为:美国红提>玫瑰香>无核白>木纳格。四种浓缩葡萄汁对红花籽油在贮藏中具有明显的抗氧化作用,当其添加量分别为0.05%,0.10%,0.05%,0.10%时达到最强的抗氧化效果。     

Pekmez: A Traditional Concentrated Fruit Product

Pekmez is a traditional Turkish food made by using different fruits such as grape, mulberry, fig, apple, and sugar beet. There are two different kinds of pekmez, either liquid pekmez or solid pekmez, produced in Turkey. The stages for processing liquid pekmez for all fruits, except mulberry, include washing, sorting, crushing, pressing, and boiling. By using liquid pekmez, and solidifying and bleaching its agents solid pekmez is produced. Pekmez is a healthful food due to its nutritional content and is used as a main source of energy based on its chemical composition. The carbohydrates in pekmez are generally in the form of natural sugars like glucose and fructose, which is nutritionally important for babies, children, sportsmen, and active workers. Pekmez production and its chemical composition should be adapted to the modern food technology and food safety requirements; at the same time, this adaptation should conserve the authentic properties of the product.