FLOW BEHAVIOR AND FUNCTIONAL PROPERTIES OF MALT EXTRACT CONCENTRATES

Flow characteristics and functional properties of malt extract concentrates were investigated. Flow behavior was studied using a coaxial viscometer over shear rates of 0.6–145.8 s^-1. The shear rate-shear stress data followed the power law, Casson, Herschel-Bulkley and Bingham plastic models. Herschel-Bulkley values for flow behavior index which ranged from 0.73–0.94, and presence of yield stress indicated the Bingham plastic nature of malt extract concentrates. The activation energy of flow for various concentrates was in the range of 14.8–17.7 kcal/gmole. Magnitudes of Reynold numbers (0.0–49.9) for all concentrates were lower than 2100. Temperature, yield stress and plastic viscosity considerably influenced the flow of concentrates in straight pipes. The pressure drop and power requirements for flow of concentrates in pipes at 50°–60°C were lower than those at 30°C, but negligibly different from those at 80°C. Coefficients of correlation between the Bingham plastic values for pressure drop and yield stress (r = 0.86, P < 0.01), and plastic viscosity (r = 0.97, P < 0.01) were highly significant. Hulled barley and corn concentrates containing high amounts of reducing sugars, showed low viscosities and yield stresses, and required desirably low power for flow in pipes at 50°–60°C. The high protein concentrates of wheat and triticale malts showed high whip volume and good foam stability. Wheat concentrate was superior in fermentability. Hulless barley and finger millet malts produced concentrates with high viscosities which might facilitate their utilization in gums, candies and other such products.     

EFFECT OF ORANGE JUICE COMPOSITION ON FLOW BEHAVIOUR OF SIX-FOLD CONCENTRATE

Abstract. The effect of the pulp content and the relative viscosity of the serum on the flow behaviour of a six-fold orange juice concentrate, as represented by the generalized Casson equation and the power law, was studied on samples prepared with a single factor varied at a time. These general flow equations, optimal in terms of multiple correlation coefficients, were established and confirmed on commercial samples. Both equations were successfully applied in predicting the flow behaviour of orange juice concentrates. The generalized Casson equation was found to be somewhat more accurate than the power law.     

Flow Properties of Low-Pulp Concentrated Orange Juice: Effect of Temperature and Concentration

Three 65° Brix low-pulp concentrated orange juice (COJ) samples, between −19 and 30°C were shear-thinning (pseudoplastic) fluids with negligible magnitudes of yield stress. The simple power law model fit welt the shear rate-shear stress data. For one sample, the Powell-Eyring model also described the data well. The Arrhenius model described the effect of temperature on the apparent viscosity and the consistency index of the power law model. The activation energy of flow (E_a) was 10.7 ± 0.2 kcal/g mole. The models of Harper and El Sahrigi and Christiansen and Craig were suitable for describing the combined effect of temperature and shear rate. The magnitude of E_a decreased with decrease in concentration. Apparent viscosity and K increased exponeitially with concentration.     

Flow Characterization of Peach Products During Extrusion

Suitability of Bingham, Herschel-Bulkley, Casson, and Mizrahi-Berk models, to characterize the flow behavior of peach products during extrusion was investigated. The Casson equation sufficiently described the flow of peach extrudates within the 49 to 125 s^-1 shear rate range. As concentration increased, yield stress and consistency coefficients increased. A rheological model was proposed to describe the viscosity of peach extrudates. The model incorporates the effect of shear rate by the Casson equation and the effect of concentration by a linear expression. The model provided good fit to the experimental data for peach extrudates reconstituted from drum-dried peach purees.     

FLOW BEHAVIOR of COOKED MAIZE FLOUR SUSPENSIONS and APPLICABILITY of MATHEMATICAL MODELS

The shear-rate/shear-stress data of cooked maize flour suspensions were obtained using a concentric cylinder viscometer in the shear rate range of 3 and 1326 s⁻¹. the effects of concentration of maize flour (2–10%) in the cooked suspensions on yield stress, flow behavior index, consistency index and apparent viscosity, were investigated. Cooked maize flour suspensions were pseudoplastic in nature with yield stress. At flour concentrations above 6%, the experimentally determined yield stresses were lower than those calculated from different rheological models. the shear-rate/shear-stress data were examined using the rheological models: the power law, Bingham plastic, Casson, Costell-Duran, Herschel-Bulkley and Mizrahi-Berk models. the last two models were found to provide the best fit (r ≥ 0.991, p ≥ 0.01).     

Changes in the apparent viscosity profiles of casein suspensions as affected by plant enzymes

The aim of this work was to study the degree of hydrolysis and changes in the apparent viscosity of casein suspensions as a result of various enzymes addition. Suspensions with 3, 12 and 15 g/100 mL of casein, at pH 5.2, 6.0 and 6.5 were prepared in buffer solutions. Previous standardization; plant (papain and bromelain) and animal (chymosin) enzymes were added to hydrolize the casein suspensions. A control with no enzyme addition was used. The rheological behaviour was determined using a rotational rheometer (Haake RV20), with a cone and plate geometry. The Casson and the power law equations were applied to the data. The degree of hydrolysis was a function of the enzyme, pH and casein concentration, presenting chymosin the highest values. All enzymes showed the highest activity at acidic pH. Also, some substrate inhibition was observed. All samples behaved as non-Newtonian, shear-thinning systems with a yield stress value. In all cases, a significant increase in the viscosity was observed when shifting from 3 to 12 g/100 mL. Further increase in concentration caused an opposite effect. Changes in pH of the casein suspensions affected the viscosity, presenting maximum values at pH 6.0. The Casson equation fitted the results better than the power law model.     

Comparison of rheological models for determining dark chocolate viscosity

Parameters in chocolate rheology, namely shear viscosity and yield stress, are important in manufacture and directly influenced by product particle size distribution (PSD) and composition. The Casson model was the standard confectionery industry strategy to quantify rheological properties of molten chocolate until in 2000, the International Confectionery Association recommended the use of interpolation data to describe viscosity. The two strategies are compared and correlated in defining rheological properties of molten dark chocolates prepared using different PSD, fat and lecithin content. Rheological parameters were determined using a shear rate-controlled rheometer and data examined using correlation, regression and principal component analyses to establish their inter-relationships. Correlation and regression analyses showed high correlation ( r  = 0.89–1.00) and regression coefficients ( R ² = 0.84–1.00). The newer International Confectionery Association technique gave higher correlation and regression coefficients than the Casson model, but multivariate principal component analysis showed that the two models were highly related and either could effectively quantify dark chocolate viscosity parameters.     

RHEOLOGICAL AND TEXTURE STUDIES OF BUTTER3

Four commercial butters (conventional batch and Westfalia, Contimab and Cherry-Burrell continuous churned) were stored at two temperatures and evaluated periodically for rheological and textural properties. Evaluation methods included four mechanical tests (quasistatic shear, quasistatic uniaxial compression, Penetrometer, and extrusion) and sensory ratings of spreadability, firmness, and other texture parameters. The first three mechanical methods produced quasistatic shear yield stress values that had close agreement. For quality control the three tests can be considered equivalent. Shear stress-strain rate data from extrusion testing developed using the Rabinowitch-Mooney equation could be represented well by the Casson model. Casson yield stress values were an order of magnitude lower than the quasistatic values. The power law equation with a yield stress also represented the butter flow well, and all four butters had similar power law exponents (approx. 0.56). The Cherry-Burrell butter had much higher quasistatic and Casson model constants than the other butters. It was also the most temperature sensitive and most stable with storage time. Temperature-shear rate equivalent effects on shear stress were demonstrated by developing shift factors. The quasistatic yield values for the butters best predicted sensory spread-ability and hardness. The changes in flow properties (Casson yield stress and Casson slope) correlated with aging.     

EFFECT OF UNIMODAL PARTICLE SIZE AND PULP CONTENT ON RHEOLOGICAL PROPERTIES OF TOMATO PUREE

The vane method in controlled shear stress mode was used to determine the yield stress and the shear rate—shear stress data of tomato purees containing 10–35% pulp of two different average particle sizes: 0.34 and 0.71 mm. Consistency index and apparent viscosity increased significantly with pulp content and decreased with average particle size. The effect of pulp weight fraction (P) on relative viscosity (η_r) could be described by the single parameter equation: η_r= [1 – (P/A)]⁻², while the effect of particle diameter on η_r could be described using Peclet number. Magnitudes of yield stress determined directly by the vane method were higher than those obtained by using the Casson model, and were proportional to the square of pulp content. Reduced Casson yield stress—P data on purees of both particle sizes followd a single curve. Effects of pulp content and particle size on vane yield stress and apparent viscosity were evident from the correlation forms with high values of R².     

Flow Behavior of Milk Chocolate Melt and the Application to Coating Flow

ABSTRACT: The rheological properties of chocolate, especially shear viscosity and yield stress, are important control parameters for enrobing processes in confectionery manufacture. The rheological parameters of molten milk chocolate were measured at 42°C during steady pipe flow using a magnetic resonance imaging (MRI) viscometric method. The experimental method combines shear rate values obtained from an MR velocity image and shear stress values obtained from an independent pressure drop measurement. The experimental factors were emulsifier type and emulsifier level. The rheogram data were fit by the Casson model to yield the Casson yield stress and plastic viscosity. The Casson yield stress ranged from 1.9 to 15.0 Pa; the Casson viscosity ranged from 6.0 to 14.6 Pa s as a function of emulsifier content. The rheological parameters were incorporated into a drainage theory model to predict coating thicknesses in the enrobing process. The model was solved numerically and yielded good approximations to the experimental values that were between 1.1 to 2.7 mm.     

糖对牛奶布丁流变性的影响

奉文采用哈克流变仪研究了不同质量分数下几种糖时鲜奶布丁体系的流变学性质,所用的糖质量分数依次为2%、4%、8%和16%,未著淀耢质量分数为6%. 结果表明:牛奶布丁是-种非宾汉塑性流体,测得的剪切速率和相应的剪切应力的关系符合Casson模型. 随着糖质量分数的提高,牛奶布丁的屈服应力、表观黏度和剪切应力均随糖质量分数的增大而增大.     

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.     

Chocolate yield stress as measured by oscillatory rheology

Liquid chocolate exhibits a non-Newtonian flow behavior that is conventionally characterized by a yield stress and plastic viscosity. In general, yield stress is determined by shear rheology experiments and the data are plotted as viscosity as a function of shear stress or shear stress as a function of shear rate. For the shear stress-shear rate plot, a frequently used approach to estimate the yield stress is to fit the data to one of several established models, with the Casson model being the most popular. Even though ICA (former IOCCC) recommendation is not to use the Casson model, it is still frequently applied. With the Casson model, a good fit to the experimental data for the shear rate ranging from 5 s^{− 1} to 60 s^{− 1} is realized. However, this model is unable to resolve real differences between chocolate samples that manifest at shear rate values below 5 s^{− 1}. In this study, oscillatory rheology was applied and the stress at the end of the linear viscoelastic region (LVR) was taken as an estimate for the yield stress. This method was shown to be sensitive to fat content, emulsifier concentration and type of emulsifier. Furthermore, oscillatory rheology was found to be capable to capture differences in yield stress of chocolates that were not differentiated using the Casson model fitting approach.     

MODELING THE TEMPERATURE EFFECT ON THE FLOW BEHAVIOR OF SWEET POTATO PUREE1

A study was conducted to investigate the effect of temperature on viscosity of sweet potato (SP) puree. Rheological data of the puree were measured using a Bohlin VOR Rheometer. Shear rates employed ranged from 0.01–921 s^?1. Thermal scans were run at 15, 25, 40, 60, 75, and 90C. The puree exhibited “shear thinning” behavior with a yield stress value of 10 Pa at each temperature tested. The characteristic of the flow behavior of the puree was determined by fitting the experimental data to Herschel-Bulkley, Casson and Modified Casson models. The model with the best fit was then used to represent the combined effect of shear rate and temperature on the apparent viscosity of SP puree in a model based upon the Modified Casson model. The model was validated using data for SP puree samples at 50C. Results showed that, within the experimental conditions used in this study, the model could adequately predict apparent viscosities of sweet potato puree processed at different temperatures.     

Flow Properties of Low-Pulp Concentrated Orange Juice: Serum Viscosity and Effect of Pulp Content

65° Brix serum samples from four concentrated orange juice (COJ) samples, between -19 and 30°C, were mildy shear-thinning fluids with negligible yield stress. The power law model described well the flow data. For one sample, the Powell-Eyring model also described the data. The activation energy of flow (E_a) for the samples was between 11.2–13.6 kcal/gmole. The power law parameters were determined for a 65°Brix sample as a function of pulp content (0–11%) between −19 and 30°C. At a fixed temperature, the apparent viscosity and the consistency index increased exponentially with pulp content. E_a decreased with increase in pulp content and reached a constant value of about 10.2 kcal/gmole. Data on a high-pulp (21.2%), 65° Brix, sample indicated the presence of yield stress, particularly at low temperatures. The Mizrahi-Berk model predicted reliable values of the yield stress.     

FLOW PROPERTIES OF BABACO (CARICA PENTAGONA) PUREES AND CONCENTRATES

A power law model describes adequately the rheological behaviour of Babaco purees and concentrates while a Herschel-Bulkley model describes concentrates only. A single equation η_a=α x cβ x exp (E_a/RT), combining the effects of temperature and concentration on apparent viscosity (η_a100), was used to describe rheological behaviour.     

EFFECT OF PROCESSING, PRESERVATION AND STORAGE ON RHEOLOGY OF GUAVA PULP

Rheological behavior of white and pink guava pulps was investigated using Rheotest 2 coaxial cylinder viscometer over shear rates of 0.6 to 145.8 s⁻¹. The shear rate-shear stress data followed the power law, Casson, Herschel-Bulkley, Michaels and Bolger models. The power law flow behavior index values were in the range of 0.14 to 0.19. Presence of measurable yield stress indicated Bingham model of the pulps. Storage of pulps for 30 weeks had negligible influence on flow behavior index values. The consistency index and yield stress values decreased with extending storage from 0 to 30 weeks. The Michaels and Bolger model distinctly described the non-Newtonian nature of cold- and hot-break pulps as well as different behavior of the pink guava pulps. The structure shear resistance values for hot-break pulps at zero shear rate were considerably higher than those of the cold-break, indicating their high pseudoplasticity.     

FLOW BEHAVIOR AND RHEOLOGICAL MODELS OF RICE FLOUR PASTES

Rheological properties of a popular Chinese rice flour pastes were determined with a rotational viscometer at different levels of concentration and temperature. The rice flour had intermediate amylose content, medium gel consistency and high birefringence-endpoint temperature (BEPT). Cooked pastes exhibited shear-thinning behavior without yield stress at the concentration levels of 2～6% and temperatures of 25～80C and their flow properties were represented by a power law model. The effects of concentration and temperature on consistency index, flow behavior index and apparent viscosity were investigated.     

RELATIONSHIP BETWEEN THE BOSTWICK MEASUREMENT AND FLUID PROPERTIES

Consistency of tomato concentrates was evaluated in a Bostwick consistometer. The concentrates were produced in a semibatch evaporator at soluble solids content from 5.3 to 24.0°Brix. The apparent viscosity, yield stress and density were measured at 20C. With respect to the gravity current analysis, the Bostwick measurement correlated well with the theoretical ratio of the apparent viscosity to density (R² = 0.96). For the concentrates with yield stress values in the range of 60–200 Pa, the predicted extent of flow based on the slump analysis was within 2% of the measured extent of flow in the Bostwick consistometer.     

Steady and dynamic shear rheological properties of sweet potato flour dispersions

Korean sweet potato flour dispersions at different concentrations (6, 7, 8, 9, and 10%) were evaluated for their steady and dynamic shear rheological properties. The steady shear rheological properties showed that sweet potato flour dispersions at 25 °C showed a shear-thinning fluid (n=0.31–0.41) exhibiting a yield stress. The magnitudes of Casson yield stress (σ_oc), consistency index (K) and apparent viscosity (η_a,100) increased with an increase in concentration. Within the temperature range of 25–70 °C, the apparent viscosity obeyed the Arrhenius temperature relationship with high determination coefficient (R ²=0.97–0.99) with activation energies (Ea) ranging 0.015–0.024 KJ/mol. Both power law and exponential type models were used to establish the relationship between concentration and apparent viscosity (η_a). Magnitudes of G′ and G″ increased with an increase in concentration. G′ values were higher than G″ over the most of the frequency range (0.63–63 rad/s), being frequency dependent. The sweet potato flour dispersions did not closely follow the Cox–Merz rule at concentrations lower than 10%.