Basim Abu-Jdayil

Modelling the time-dependent rheological behavior of semisolid foodstuffs

Abstract Many of food products exhibited the thixotropic behavior, in which, the apparent viscosity of material decreases with time of shearing at constant shear rate. The structural kinetic model (SKM) was used to characterize the thixotropic behavior of three different kinds of food products. Foods selected for analysis represent the fluid and semisolid food materials. They include milled sesame, concentrated yogurt and mayonnaise. The SKM postulates that the change in the rheological behavior is associated with shear-induced breakdown of the internal structure of the food product. This model for the structure decay with time at constant shear rate assumes n th order kinetics for the decay of the material structure with a rate constant, k . The dependence of the degree and the extent of thixotropy of the materials on the temperature, composition and shear history of the food product was determined.

Rheological properties of plain yogurt during coagulation process: impact of fat content and preheat treatment of milk.

A study of the effect of fat content and preheat treatment of milk has shown their respective effects on the rheological behavior of curd during the coagulation process of plain yogurt. Increase in fat content leads to an increase in viscosity. The highest viscosity was manifested by milk heated at 137°C while the lowest value was exhibited by milk heated at 65°C. The process viscosity curves for three different stages are described by mathematical relationships. Finally, a two-parameter power law model was used to describe the flow behavior of the yogurt during coagulation.

Experimental and modelling studies of the flow properties of concentrated yogurt as affected by the storage time

Abstract The effect of storage time on the flow properties of concentrated yogurt (labneh) was investigated using a rotational viscometer. Commercial labneh samples were stored at 8 °C. Experiments were performed at 25 °C after 0, 1, 2, 5, 8, 10 or 14 days after the packaging date. The apparent viscosity of fresh sample was then measured as a function of shear rate. For a given shear rate, the apparent viscosity was measured as a function of shearing time. The completely destructed labneh flow properties were also measured after subjecting the labneh samples to a high shear rate for 2 h. The increase in the apparent viscosity of fresh labneh with storage time is attributed to the further development of the gel structure occurred. It was also found that, labneh samples exhibited shear-thinning and thixotropic behaviours with different storage times. The shear-thinning behaviour is fitted well by the power-law model, and the effect of storage time on the power-law parameters was determined. The thixotropic behaviour of labneh was modelled using the structural kinetic approach. For the completely destructed labneh, the effect of storage time on the flow properties was insignificant, and the flow properties were modelled well by the power-law model.

Heat effect on rheology of light- and dark-colored honey

Abstract The effect of temperature and time of constant temperature heating ( t CTH ) on the rheological properties of light and dark types of honey was examined. Honey samples were heated up to 40°C, 60°C, 80°C or 94°C, and hold for 5, 10 or 20 min, and their viscosities were then measured either immediately at the heating temperature or after being cooled overnight, where measurements were carried out at 25°C and 35°C as a function of the shear rate. The types of honey used were identified via assessing the source of the nectar using pollen analysis (Melissopalynology). It was found that both honey types behave like a Newtonian fluid regardless of the conditions of heating. The time of heating required to reach the desired ultimate temperature correlates with the water content of the fresh, untreated sample. A light-colored, low water-content, heat-treated honey showed a change in viscosity only at higher heating temperatures when compared with the fresh untreated control sample. On the other hand, a dark-colored, heat-treated honey showed a change in viscosity at all levels of heating temperature. In general, the viscosity of a heat-treated honey increases with increasing ultimate heating temperature and t CTH .

RHEOLOGICAL PROPERTIES OF SELECTED LIGHT COLORED JORDANIAN HONEY

The rheological properties of Apple, Besromia, Citrus, and Ziziphus types of light colored Jordanian honey were examined. The types of honey used were identified via assessing the source of nectar using pollen analysis (Melissopalynology). The moisture content of honey samples was indirectly assessed via measuring the refractive index of the sample using a refractometer. A rotational, concentric cylinder viscometer was used to measure rheological properties of honey samples. The apparent viscosity was measured as a function of the shear rate. In addition, the apparent viscosity was measured, at constant shear rate at 2.2 s−1, as a function of shearing time. Newtons law of viscosity was found to adequately describe the flow behavior of honey samples. The apparent viscosity was found to decrease with temperature, and the temperature dependency of viscosity was found to follow the Arrhenius model. Moreover, the viscosity was also found to decrease with moisture content of honey. An exponential fit was used to describe the water content dependency of viscosity.

A Comparative Study of Rheological Characteristics of Tomato Paste and Tomato Powder Solutions

Abstract The flow curves and time-dependent flow properties of tomato paste and tomato reconstituted solution (TRCS) were assessed in this study at different concentrations and temperatures. The tomato-reconstituted solution was prepared by dissolving the powders (produced by the spray drying technique) in certain amount of water to provide the concentration required. Bingham model was found to be the most appropriate to fit the flow curves of tomato paste. The yield stress, τ B , significantly increased with concentration and decreased with temperature in both the forward- (increasing shear rate) and backward-measurements (decreasing shear rate). The Bingham viscosity, η B , was found to increase with concentration and decrease with temperature. As for the TRCS, the flow curves were also best fitted by the Bingham model with shear stress values significantly less than that of tomato paste at the same concentration and shear rate. Tomato paste solutions showed a time-dependent rheological behavior while the TRCS showed a time-independent behavior. Tomato paste exhibited a thixotropic behavior at low shear rates and converted to an anti-thixotropic behavior at high shear rates.

Effect of solids concentration on the rheology of labneh (concentrated yogurt) produced from sheep milk

Abstract The effect of solids concentration on the apparent viscosity of labneh made from sheep milk has been investigated using a rotary viscometer. Sheep labneh was manufactured following the traditional method by using cloth bags. Apparent viscosity of labneh with four different solids concentration was studied as a function of the shear rate. It is found that sheep labneh with different solids concentration exhibits shear thinning and thixotropic behavior. The power law model was found to fit the apparent viscosity––shear rate experimental data, satisfactorily. Both the consistency coefficient and the flow behavior index were correlated as a function of solids concentration. The predicted apparent viscosity showed an absolute average error of less than 5%. Time-dependent viscosity measurements were performed at four different shear rates. Using the structural kinetic approach, a 1.5-order kinetic model was found best for correlating the experimental data. Completely destructed labneh, after 4-h preshearing, was also studied as function of shear rate. Comparison between labneh made from cow milk and sheep milk was performed, whenever data were available.

Effect of glucose concentration on the rheological properties of wheat-starch dispersions

The effect of glucose addition and time of constant temperature heating (tCTH) on the rheological properties of starch dispersion systems was examined. A fixed starch mixture of 5% (w/v), and glucose concentrations of 0‐6% (w/v) were used. The starch dispersion was heated up to 808C, then was kept, at this temperature, for a period of 0, 10, 20, or 30 min. The apparent viscosity was then measured as a function of shear rate. In addition, the apparent viscosity was measured, at constant shear rate of 106 s 21 , as a function of shearing time. The Herschel‐ Bulkley model Ota t0 1 m_ g n U was used to fit the flow behavior of starch dispersions. It was found that the flow behavior index, n, approaches unity (Bingham model) for most of the data. It was also found that as tCTH was increased, for a given glucose concentration, both yield stress, t 0, and consistency coefficient,m, increased. The presence of glucose also resulted in an increase of both t 0 and m .A t 6% glucose concentration, samples with tCTH of 30 min showed the highest anti-thixotropic behavior. The apparent viscosity of starch dispersions at tCTH of 0 min had the lowest value at all levels of glucose concentrations. In general, the presence of glucose resulted in an increase in the apparent viscosity compared to that of glucose-free starch dispersions. q 2000 Elsevier Science Ltd. All rights reserved.

Effect of cooling rate on unseeded batch crystallization of KCl

Abstract Effect of three different cooling rates is investigated on crystallization kinetics of potassium chloride. The gravimeric method is used to measure the concentration of potassium chloride in the liquid phase as a function of time. The method proved to be simple and accurate. A non-linear optimization method is applied to estimate the growth and nucleation rate parameters from unseeded batch cooling crystallization experiments. The effect of the cooling rate profiles on the parameters and on the final mean particle size is discussed.

Study on Bentonite-Unsaturated Polyester Composite Materials:

Jordanian Ca-bentonite was used in formulation of unsaturated polyester-based composite materials. For curing purpose, methyl ethyl ketone peroxide was used as an initiator and it was accelerated with cobalt octoate to maximize the curing process at room temperature. The effect of filler and styrene contents on the physical properties of composites was assessed by measuring the compressive strength, hardness, thermal conductivity, water absorption capacity, and apparent density. Increasing the filler content, at a constant styrene/polyester ratio, increased the properties of composites. On other hand, maximum values of compressive strength, hardness, and thermal conductivity of composites were found at about 22.7 wt% of styrene, whereas water absorption capacity was minimum at a styrene content of 32.8 wt%. Nevertheless, the apparent density was found to linearly decrease with styrene content.