Effect of temperature and concentration on Rheological properties of “Kesar” mango juice

Flow characteristics of juice of “Kesar” mango have been investigated and rheological parameters were evaluated using rotational viscometer at temperature 20, 30, 40, 50, 60 and 70°C at concentration of 7.6%, 11.69%, 16.37% and 26% total solid. The experimental results followed the power law model for the best fit and the values of flow behaviour index (n) was less than unity (0.20–0.33) at all temperature and concentration revealing the shear-thinning (pseudoplasticity) nature of juice. An obvious correlation between consistency coefficient, in the range of 0.32–80.09 Pa sⁿ and inverse absolute temperature has been exhibited by Arrhenius model. Power equation indicated that consistency coefficient increased non-linearly with increase in concentration. The magnitude of activation energy were found in the range of 3.8–13.7 kJ/mol K.     

Rheological properties of African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) calcium proteinate and isoelectric protein isolates

The rheological characterizations of African yam bean (Sphenostylis stenocarpa) protein dispersions were investigated. Isoelectrically precipitated protein-IP_alk and IP_salt isolates obtained from alkaline and salt extractions respectively were more soluble than calcium precipitated proteins (CaP_alk and CaP_salt) at pH 3, 7 and 8. Regression analysis showed that Power law, Casson and Bingham rheological models adequately described rheological behaviors of S. stenocarpa protein dispersion. However, Power law gave the best fit. The flow behavior indices (n), at different ionic strength, pH, and temperature media were less than unity, indicating that S. stenocarpa protein dispersion exhibited pseudoplastic behaviors under the conditions tested. Salt extracted proteins were more pseudoplastic than alkali extracted counterpart with n for salt extracted proteins (IP_salt & CaP_salt) lower than that of alkali extracted protein (CaP_alk & CaP_salt). This is a numerical indication that salt extracted S. stenocarpa proteins were of larger shear-thinning tendency than the alkali extracted proteins. The consistency coefficients, k of isoelectrically precipitated protein (0.305-0.327 Pasⁿ) were significantly (P < 0.05) higher than that of calcium proteinates in the range ranged 0.167-0.180 Pasⁿ. Both isoelectrically precipitated proteins and calcium proteinates exhibited yield stress, however, isoelectrically precipitated S. stenocarpa protein exhibited significantly (P < 0.05) higher yield stress (0.275-0.308 Pa) than the calcium proteinates (0.148-0.165 Pa). The effect of temperature on apparent viscosity of the proteins was evaluated using an Arrhenius-type equation. The activation energies (E_a) obtained were in the range 33-51.2 and 42.6-55.5 Jmol⁻¹ for calcium proteinate and isoelectrically precipitated protein respectively.     

Characterization of rheological properties of systems containing sugar substitutes and carrageenan

The effects of addition of κ-carrageenan to solutions containing 40% (w/w) sugar substitute on the rheological properties of these systems were investigated at 25 °C using a rotational viscometer at rotational speeds of 6, 12, 30, and 60 rev min⁻¹. The flow behaviour of the solutions was adequately described by the power law model with or without yield stress. The consistency index ( K ) and the flow behaviour index ( n ) were determined from shear stress vs. shear rate data. The flow parameters of the solutions depended on the carrageenan concentration. The apparent viscosities of the systems decreased with increasing shear rate, indicating pseudoplastic behaviour. The final carrageenan concentration was found to be an effective factor controlling the degree of sliminess of the model food systems studied.     

Rheological Properties of Liquid Egg Products (LEPS)

Rheological properties were determined at 4°C (refrigerated temperature), 25°C (room temperature), 60°C (pasteurization temperature) for liquid whole egg (LWE) and liquid egg yolk (LEY) and 4, 25, 55.6°C for liquid egg white (LEW) by using concentric cylinder viscometer. The shear rate range was 8 to 53.7 s^?1 for LEW and LWE, and 1 to 34 s^?1 for LEY. Selected physical properties (e.g., density) of LEPs were studied at broad range of temperatures from 4°C to 60°C. All liquid egg products (LEPs) exhibited mildly shear thinning (pseudoplastic) behavior. Experimental data of LWE and LEW successfully fitted Herschel-Bulkley model, LEY data were well described by power law model. LEW and LWE showed thixotropy and time-dependency at their pasteurization temperatures (55.6°C for LEW, 60°C for LWE) and considered being time-independent below these temperatures. LEY exhibited time-dependent behavior at 4°C and 60°C. But its rheological behavior showed no thixotropy and time-dependency at room temperature. The density of all three products decreased with increasing temperature. Density data were correlated by polynomial models (r² > 0.99).     

Rheological behaviour of emulsions of avocado and watermelon oils during storage

Rheological properties of emulsions made out of avocado pulp and watermelon seed oils with whey protein concentrate were determined during different storage periods. The oils, as well as the emulsions behaved like non-Newtonian liquids, having shear-thinning characteristics. Both oils showed moderate shear-thinning characteristics as the flow behaviour indices were between 0.86 and 0.88. The shear-rate/shear-stress data could be adequately fitted (r = 0.997–0.999) to a common rheological equation, e.g. the power-law model. Avocado pulp oil was markedly more viscous than was watermelon seed oil which was also evident from the higher apparent viscosity and consistency index values.     

纤维素氨基甲酸酯溶液的流变性能

 探讨纤维素氨基甲酸酯（CC）溶液的流变性能及其影响因素.结果表明：含氮量小于3.57%的CC氢氧化钠溶液,在所研究的CC浓度范围内表现为切力稀型流体,非牛顿指数小于1,且随着CC溶液浓度的增加而减小;表观黏度随剪切速率的增加而降低,随CC溶液浓度的增加而呈指数关系上升,并得到了经验公式;结构黏度指数随CC溶液浓度的增加而缓慢增大,但当CC质量分数超过5.66%后呈非线性迅速增大,溶液流变性变差;纤维素氨基甲酸酯溶液纺前处理温度对其流变性能影响显著,当前处理温度高于15℃,溶液流变性能恶化,可观察到溶液呈凝胶状.     

Intrinsic Viscosity and Flow Behaviour of Arabic Gum Aqueous Solutions

The intrinsic viscosity and flow behaviour of aqueous solutions of different concentrations of Arabic gum were studied. The molecular weight of this polymer was calculated using the value of the intrinsic viscosity, employing both Huggins and Kramer and Mark-Houwink equations. The value of the apparent viscosity and the influence of the shear rate on the rheological behaviour of different polymer concentrations in aqueous solution were determined. The effect of temperature over the flow behaviour was also studied. The Ostwald model has been employed to fit the experimental data and model parameters have been obtained.     

Effect of Particle Size,Temperature, and Total Soluble Solids on The Rheological Properties of Watermelon Juice: A Response Surface Approach

Central composite design was used to analyze the effect of particle size (0.075, 0.15, 0.25, 0.355, 0.425 mm), temperature (1.6, 5, 10, 15, 18.4°C) and total soluble solids (14.77, 25, 40, 50, 65.23°Brix) on the rheological properties of watermelon juice. Experimental values of consistency coefficient k, varied from 0.178–0.628 Pa sⁿ and flow behavior index n from 0.281 to 0.949. Regression equation was computed and used to predict the values of k and n. Results revealed that coefficient of determination (R²) and standard error for consistency coefficient k were 0.84 and 0.043 and for flow behavior index n were 0.42 and 0.102 respectively. Surface graphs showed that k value increased with increase in total soluble solids and particle size while decreased with temperature.     

二醋酸纤维素纤维纺丝溶液流变性能

为研究二醋酸纤维素纤维纺丝成形工艺,采用Physica MCR101流变仪测试二醋酸纤维素纤维纺丝溶液的质量分数、温度与剪切速率之间的变化关系,得到纺丝溶液的流动曲线.在此基础上,模拟分析出纺丝溶液的非牛顿指数、结构黏度指数和黏流活化能等流变参数.结果表明:二醋酸纤维素纤维纺丝溶液为切力变稀非牛顿流体,随着溶液温度的升高,溶液的表观黏度和结构黏度指数减小,非牛顿指数增加;随着溶液质量分数的增加,溶液的表观黏度和结构黏度指数呈现增大趋势,而非牛顿指数和黏流活化能逐渐减小.     

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.     

Rheological behaviour and colour changes of ginger paste during storage

Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high‐density‐polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20–80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s^?1 in 3 min, followed by a steady shear at 200 s^?1 for 3 min and finally decreasing linearly from 200 to 0 s^?1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel–Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol^?1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers.     

浓缩石榴汁流变特性研究

研究了不同浓度的石榴汁在不同温度下的流变特性。结果表明:在实验范围内,石榴汁表现为胀塑性流体,通过回归分析,温度对表观粘度的影响可以用Arrhenius方程表示,浓度对表观粘度的影响可以用指数方程更好地表示,并推导出温度和浓度对表观粘度综合影响的方程式。该方程的建立可以用来预测实际加工过程中一定温度和浓度时石榴汁的表观粘度。      

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

In-Line Measurement of Rheological Parameters and Modeling of Apparent Wall Slip in Diced Tomato Suspensions Using Ultrasonics

ABSTRACT: Rheological behavior of a slurry consisting of 1- to 3-mm diced tomatoes suspended in tomato juice was evaluated by an in-line measurement method based upon ultrasonics. This technique permitted the measurements of yield stress, consistency index, and apparent wall slip. The suspension exhibited a yield stress at every flow rate studied, and its value was found to be 0.79 ±0.11 Pa. The shear viscosity at different shear rates was obtained in-line without assuming a specific constitutive equation. A comparison of Herschel-Bulkley, Power Law, Bingham Plastic, and Casson models showed that this suspension was best characterized with the Herschel-Bulkley model. The apparent wall slip region was successfully modeled as a Bingham fluid. This study shows the usefulness of this method for in-line characterization of particulate tomato products.     

A multiple-step slit die rheometer for rheological characterization of extruded starch melts

Extrusion cooking is a very important process in the field of cereal and snack manufacturing. The rheological properties of the starch based matrix strongly influence this process. A newly developed online rheometer was mounted on a twin screw extruder in order to measure these properties. It was possible to obtain viscosity of wheat flour and corn grits at typical extrusion cooking conditions over a shear rate range of three decades. Flow curves for varying screw speed and water content at a constant thermomechanical history of the starch were measured. Also the temperature dependence of the apparent viscosities could be determined showing activation energies in the range found for synthetic polymers. Furthermore, additional pressure drops that occur at step changes of the slit height were detected. Thus, it was possible to evaluate visco-elastic properties of extruded starch melts at different extrusion cooking conditions.     

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.