Rheological Properties of Cabbage Pulp

The rheological behavior of cabbage pulp was determined using a computer controlled rotational rheometer at a temperature range of 20, 30, 40, and 50°C. The flow behavior of pulp was pseudoplastic and fitted well to the Casson model. In all the cases, the effect of soluble solids on apparent viscosity was more pronounced than the effect of temperature. The combined effect of temperature and soluble solid content on viscosity was also given. The activation energy value of 3–6°Brix cabbage puree varied from 7 to 12.6 kJ/mol when shear rate increased from 1 to 10 s^?1. The exponential model developed had an excellent fit (r² > 0.87) and would be useful for the engineering applications.     

Rheological behavior of blueberry (Vaccinium ashei) purees containing xanthan gum and fructose as ingredients

In the present work the influence of temperature, xanthan gum and fructose addition on rheological behavior in steady state of blueberry puree was evaluated. The blueberry pulp was formulated with addition of xanthan gum (1.6, 2.0, 2.5, 3.0 and 3.3%) and fructose (6.6, 10.0, 15.0, 20.0 and 23.4%). Rheological data were obtained by shear rate scan tests in a rotational rheometer, with geometry of concentric cylinders in temperatures of 27, 40, 60, 80 and 93 °C. The thixotropy analysis was made through the calculation of the difference between the areas under up and down cycles’ flow curves. The analysis of the formulation influence on puree viscosity was carried out in two stages: i) selection of an appropriate rheological model for representation of data obtained in experiments and ii) statistical analysis of formulation and temperature influence on rheological parameters of selected model. Three 2-parameter models (Bingham, Ostwald–de Waele and Casson) and three 3-parameter models (Herschel–Bulkley, Mizrahi–Berk and Sisko) were tested. Based on the values of correlation coefficients and variance of the estimated parameters, Casson model was chosen for fitting of experimental data. The content of xanthan gum appears as a determinant variable of the rheological behavior of the puree, both at short and long times. The correlation among the variables studied was represented through statistical models which could be used for the development of formulations with specified viscosity in the range of additive concentrations studied.     

Time-independent and time-dependent rheological characterization of vegetable-based infant purees

Flow behavior of vegetable-based infant purees was analyzed at different temperatures (5–65 °C) giving particular attention to their time-dependent properties in a shear rate range (5–200 s⁻¹). Power law model parameters describing flow behavior of samples depended on kind of infant puree, its water content and measurement temperature. Arrhenius model was used to explain temperature effect on apparent viscosity at 50 s⁻¹. Infant purees exhibited thixotropic behavior for all temperatures tested. For the same temperature, differences in hysteresis loop magnitudes were observed among purees, being more noticeable at lower temperatures. Two models were used to describe the time-dependent behavior, namely Weltman model, and second-order structural kinetic model. For all infant purees, the initial shear stress and the extent of thixotropy increased and decreased significantly with increases in shear rate and temperature. The breakdown rate of puree associations also accelerated at higher shear rates, but no trend was observed with temperature.     

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%.     

EVALUATION OF SWEET POTATO CULTIVARS AND HEATING METHODS FOR CONTROL OF MALTOSE PRODUCTION, VISCOSITY AND SENSORY QUALITY

Two varieties of sweet potato were subjected to four cooking temperature‐time combinations. A fifth treatment involved adding maltose syrup. Raw comminuted sweet potato mash and cooked sweet potato puree were evaluated for total solids, alcohol insoluble solids, commonly occurring sugars, viscosity (puree only) and for starch gelatinization temperatures. The uncooked Owairaka Red variety was higher in total solids and in alcohol insoluble solids than the Toka Toka Gold. With the exception of the cooked puree with added maltose, baking at 200C resulted in puree with the highest maltose levels. A very fast cooking procedure tended to result in puree with lower levels of maltose and high viscosity. Sensory studies revealed that the Owairaka Red variety produced puree with more viscous and adhesive mouth feel. It was concluded that cooking alone could not be used to optimize both maltose production and viscosity.     

甘薯泥粘度数学模型预测

考察了不同干物浓度和不同温度下甘薯浆的流变学特性。结果表明,甘薯浆属于典型的假塑型流体,且干物浓度和温度对其黏稠系数影响显著,幂律模型可以较好地拟合甘薯浆流动行为。甘薯浆表观黏度随着温度和剪切速率的增加而逐渐下降,呈现剪切变稀的趋势。建立了影响因子为温度和干物浓度的数学模型来预测甘薯浆的表观黏度,采用平均百分误差、卡方检验、建模效率等统计学参数对该模型评估发现其拟合精度较高。     

Effect of blanching and thermal preservation on rheology of curry leaf puree

Curry leave (sweet neem) is a herb having a variety of medicinal and food uses. The leaves are perishable and have short shelf life, hence required the need of preservation. Thermal preservation (blanching), the most commonly used technique for preservation, could be effective preservation technique leading to the destruction of microorganisms responsible for spoilage but leads to a negative effect on color loss of leaves. There is a need to search for most effective blanching techniques that lead to less color loss. In the present paper, the effect of different blanching methods on the color of curry leave was presented. The importance of the effect of homogeneity and leave dimension is also presented. The color loss during blanching is monitored through the kinetics of degradation along with the final loss of color. steady state rheological properties of the puree were resolved at various temperature levels (278, 288, 303, 318 K). Curry leaves puree showed shear thinning behavior and Ostwald-de Waele demonstrate best-defined flow behavior of the sample (R²?≥?0.9880) at various temperature levels. A decrement of consistency index and apparent viscosity values (η₅₀) at a shear rate 50 s^?1 with increment in temperature level showed by the puree.     

FLOW BEHAVIOR OF GUAVA PUREE AS A FUNCTION OF TEMPERATURE AND CONCENTRATION

Flow behavior of guava puree was determined with a tube viscometer. The puree samples (9.8-16.0° Brix) exhibited shear-thinning behavior. The flow behavior index of the power law model was nearly constant for all the samples over a temperature range of 25-60°C; its mean value was 0.43 with a standard deviation of 0.031. The apparent viscosity decreased with increase in temperature and the activation energy offlow was found to be 3.7 kcallg mole. The apparent viscosity increased as the concentration of the purees was increased; the increase was proportional to concentration raised to a power of 2.7. The Mizrahi-Berk model described well the flow data of the purees. The magnitude of the shear rate exponent was about 0.48, indicating that the purees were suspensions in shearthinning media.     

果胶酶对甘薯浆流变学行为的影响

采用中心组合设计和响应面分析法研究不同处理时间(16～134min)、处理温度(20～70℃)和加酶量(0.005%～0.105%,m/m)下果胶酶对甘薯浆流变学行为(屈服应力、流动性特征指数、黏稠系数)和表观黏度的影响。结果表明：未经果胶酶处理和经过果胶酶处理的甘薯浆均为非牛顿性流体、呈现假塑性同时具有屈服应力。Herschel-Bulkley 模型可以较好的拟合剪切应力和剪切速率的相关性;研究发现,果胶酶处理使甘薯浆的非牛顿性流体流变行为减弱,同时其表观黏度随着果胶酶浓度的增加而逐渐降低。经过果胶酶处理后的甘薯浆的表观黏度最小值为71.56mPa·s,对应的酶浓度为0.1%,酶处理时间为70.56min,酶处理温度42.34℃。     

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.     

Improved Aseptically Filled Sweet Potato Purees

A high quality sweet potato puree with better color stability than frozen purees was produced by flash sterilization followed by aseptic packaging. Starch conversion time was shortened by slicing the sweet potatoes and accurately controlling the temperature during conversion. Processing of inoculated purees for 13 sec at 138°C followed by aseptic filling was adequate for commercial stability. The effect of several processing variables on puree and sweet potato souffle quality was examined. Improved quality and storage stability of sweet potato purees were accomplished by flash sterilization at very high temperatures followed by aseptic packaging.     

Flow behaviour of carrot puree: modelling the influence of time,temperature and potato flakes addition

Rheological properties of carrot puree were investigated in the 1–1000 s^?1 shear rate range with the objective of modelling the influence of time, temperature and addition of potato flakes on the flow behaviour. Carrot puree exhibited a shear‐thinning behaviour that was well described by the Ostwald‐de Waele (Power Law) model with a flow behaviour index of 0.34 (±0.02) at 20 °C. The time‐dependent behaviour was characterised by a second‐order Structural Kinetic Model. The decay of the structural parameter with time was found to be independent of shear rate. The Arrhenius model was used to explain the effect of temperature in the range from 4 to 60 °C. The dry matter was increased by adding potato flakes (0–5%). A power law model (for the concentration) and the Arrhenius relationship (for the temperature) were combined to simultaneously describe the effects of temperature and concentration. This study provides essential data for equipment and process design.     

Effect of blanching on thermal color degradation kinetics and rheological behavior of rocket (Eruca sativa) puree

Rheological behavior and green color retention are important parameters during thermal processing of pureed leafy vegetables. In this study, an attempt was made to investigate thermal effect on the color and rheological characteristics of rocket (Eruca sativa L.) purees made from leaves with and without stems. The color degradation kinetics of rocket puree was studied at temperatures between 60 and 110 °C using fractional conversion technique. The degradation kinetics of puree followed a 1st order reaction kinetics and the activation energy values for puree with and without stems were ranged between 38.90 and 51.21 kJ/mol. Effects of blanching on oscillatory and steady flow rheology of puree made from leaves with and without stems were studied in the temperature range of 25 to 70 °C. All puree samples exhibited an elastic modulus that is larger than the loss modulus in the tested frequency range. Blanched leaf puree exhibited the highest mechanical strength at 70 °C. The steady flow data fitted the Herschel–Bulkley model well. The complex viscosity and the apparent viscosity at similar frequency and shear rate range failed to follow the Cox–Merz rule. Scanning electron microscopy and sieve-analysis revealed that the leaf puree had smaller particle sizes than puree with stems.     

RHEOLOGICAL CHARACTERIZATION OF SALAD DRESSINGS. 1. STEADY SHEAR, THIXOTROPY AND EFFECT OF TEMPERATURE

Shear stress-shear rate data of five commercial salad dressings at 2.0, 10.0, 18.3, 26.7, 32.2 and 43.3°C were obtained using a concentric cylinder viscometer. The power law and Casson equations were applicable for all products (r ≫ 0.98). The Arrhenius equation was applicable for the effect of temperature on the apparent viscosity at 100 s^−l (r ≫ 0.97). Rheological data were obtained at a constant shear rate of 275s^−l at 2.0 and 10.0° C. The results show that the Weltman equation was better than the Hahn equation in describing the thixotropic behavior of the five salad dressings.     

HIGH TEMPERATURE RHEOLOGY OF TOMATO PUREE AND STARCH DISPERSION WITH A DIRECT-DRIVE VISCOMETER

A direct-drive concentric cylinder viscometer in a pressure chamber was used to study the flow behavior of a 11 Brix tomato puree at several temperatures in the range: 76 to 120C. The activation energy of flow of the tomato puree, based on apparent viscosity at 50 s^?1, was: 9.4 kJ mol^?1. The apparent viscosity (η) versus temperature profiles of a 4.0% waxy rice (WR) starch dispersion were determined during continuous heating from 30 to 110C at six shear rates in the shear range: 114 to 644 s^?1; beginning at about 95C, significant increase in η_a was observed at 114 and 160 s^?1. The said profiles collapsed to a single curve when η_a values were converted to reduced viscosity, values of η of the starch dispersion were lower than those of η* at about the same shear rates, γ=5.7 s^?1 and ω=6.3 rad s^?1.     

Rheological and Textural Characteristics of Date Paste

The rheological properties of two commercial date pastes were investigated in the temperature range of 20–70°C. From typical flow behavior curves, it was observed that date pastes exhibited pseudoplastic behavior. The shear stress-shear rate data were fitted using six common rheological models. The Casson model best described the experimental data at all temperatures. The Arrhenius model described successfully the temperature dependence of apparent viscosity of date pastes (R² > 0.99) with an E_a value in the range of 25,392.6–25,485.7 kJ/kmol. The textural attributes measured were: hardness, springiness, gumminess, cohesiveness, chewiness, and adhesiveness for the texture profile analysis test, and firmness, adhesive force, mean load, and total positive area for the Ottawa test. There was a significant difference in textural attributes between two varieties of date paste studied. Texture profile analysis results showed that all parameters obtained for black date pastes were higher than golden date pastes except for springiness and cohesiveness. However, the Ottawa results showed that golden date pastes were firmer and less adhesive than black date pastes.     

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.     

Microbial growth and the effects of mild acidification and preservatives in refrigerated sweet potato puree

Refrigerated sweet potato puree is a convenient form of sweet potato that can be used as an ingredient in formulated foods. The microbiology of refrigerated sweet potato puree during storage for up to 5 weeks was evaluated. Because the puree was made by comminuting steam-cooked sweet potatoes before refrigeration, no naturally occurring vegetative bacterial cells were detected during a 4-week period of refrigerated storage at 4 degrees C. However, if postprocessing microbial contamination of the puree were to occur, contaminating microorganisms such as Listeria monocytogenes could grow during refrigerated storage. The effects of acidification or the addition of potassium sorbate and sodium benzoate on a population of L. monocytogenes inoculated into refrigerated (4 degrees C) sweet potato puree were determined. Inoculation of the refrigerated puree with L. monocytogenes at 10(6) CFU/ml resulted in a 3-log increase after 3 weeks storage of nonsupplemented puree. Supplementation of the sweet potato puree with 0.06% (wt/vol) sorbic acid or benzoic acid plus mild acidification of the sweet potato puree with citric acid to pH 4.2 prevented growth of L. monocytogenes during storage at 4 degrees C.     

EFFECTS OF PUREE PROCESSING METHODS ON THE TEXTURAL CHARACTERISTICS OF AN ALGINATE- TEXTURIZED SWEET POTATO PRODUCT1

The objective was to determine the effect of sweet potato (SP) puree preparation methods on the properties of texturized SP products. The treatments were separated into two main types in which sliced SPs were cooked prior to puree preparation, or purees were prepared by grinding raw roots, followed by heat processing using steam injection. Purees from each treatment were texturized into cylinders 12.7 cm long and 5.5 cm in diameter, using an alginate-calcium system, and frozen. We found that cooked purees prepared by steam injection of raw purees had higher viscosities than did purees made from cooked SP. Texture Profile Analysis (TPA) revealed that texturized product made from SP cooked before puree preparation was the most fracturable and least springy of the texturized products. Sensory panelists did not express apreference for texturized product from any of the treatments, but 23% of the panelists noted a grainy texture and/or raw root aroma in products prepared by steam injection of raw purees. In view of these observations and the fact that puree preparation from cooked SP is the simplest process, this process appears to be the best for this type of texturized SP product.     

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.