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 property of globulin from red bean (Phaseolus angularis)

Red bean globulin (RBG) dispersions exhibited pseudoplastic behavior, and the flow data were fitted to the power-law model. With increasing protein concentration, there were progressive increases in consistency coefficient (m), apparent viscosity and yield stress, suggesting protein–protein interactions. The flow behavior index (n) was decreased indicating enhanced pseudoplasticity. Ionic strength affected the flow behavior of RBG, with a reversal in its effect at a specific salt concentration (0.5–1.0 M). Addition of chaotropic salts and protein structure perturbants (urea, sodium dodecyl sulfate and dithiothreitol) caused changes in flow behavior, probably due to dissociation of the oligomers and protein unfolding. Pre-heat treatments at a temperature of 80°C, above the onset temperature of RBG, caused dramatic decreases in n and increases in m and apparent viscosity suggesting protein denaturation/aggregation. When RBG dispersions were heated from 25 to 90°C at a fixed rate (1.7°C/min), there was an initial decrease in apparent viscosity, probably due to a lowering of medium viscosity. The viscosity started to increase at around 78°C, the onset temperature of RBG; and sharp increases were observed from 80 to 90°C. Changes in apparent viscosity with increasing temperature (25–60°C) obeyed the Arrhenius law, with similar E_a values at three different shear rate values, suggesting little temperature dependence of viscosity at lower temperature range.     

Effect of Octenylsuccinylation on Rheological Properties of Corn Starch Pastes

Rheological properties of corn starch octenylsuccinate (OSA starch) pastes (5%, w/w), at different 1‐octenylsuccinic anhydride (OSA) contents (0, 1.0, 1.5, 2.0 and 2.5%, w/w) were evaluated in steady and dynamic shear. The OSA starch pastes had high shear‐thinning behaviors and their flow behaviors were described by power law, Casson, and Herschel‐Bulkley models. Magnitudes of consistency index (K, K_h) and yield stress (σ_oc, σ_h) increased with the increase in OSA content and the decrease in temperature. Over the temperature range of 10–50°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 10.7–13.9 kJ/mol) of OSA starches were lower than that (E_a = 15.9 kJ/mol) of native starch. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of OSA starch pastes increased with the increase in OSA content. Dynamic (η^*) and steady shear (η_a) viscosities of OSA starch pastes at various OSA contents did not follow the Cox‐Merz superposition rule.     

Some Physical,Chemical, and Rheological Properties of Sweet Sorghum (Sorghum Bicolor (L) Moench) Pekmez (Molasses)

Some physical, chemical properties and the rheological behaviour of the sweet sorghum (Sorghum bicolor L Moench) pekmez (molasses) were determined. The rheological behaviour of the sweet sorghum pekmez (concentrated sorghum juice) with different soluble solid contents (75.1, 72.4, 66.5, and 59.4 °Brix) was determined in the temperature range of 10, 20, 30, 40, and 50°C using a rotational viscometer equipped with spindle 5 at the speed (share rate) of 5, 10, 20, 50, and 100 rpm. An empirical power law model was used to describe the rheological behavior of the sweet sorghum pekmez with correlation coefficients (R²) between 0.922 and 0.986. The sweet sorghum pekmez exhibited a pseudoplastic behavior. An Arrhenius equation was used to describe the effect of temperature on viscosity and E_a value of the sweet sorghum pekmez was calculated as 31 350 J/mol. Depending on the soluble solids contents, the activation energies for flow of diluted samples vary from 52.27 to 24.50 kJmol^?1. The effect of °Brix on viscosity can be described by the power-law equation. Experimental data were fitted to power law and exponential model in order to describe the effect of temperature and soluble dry matter content. Density and Electrical conductivity were measured 1.3915 g/cm³ and 13.53 mS/cm, respectively. The color as L, a and b value were measured 19.07, + 4.0, and + 2.18, respectively.     

Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that (E_a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E_a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage (G′) and loss (G′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G′ and G′′ increased with the increase in gum concentration. Dynamic rheological data of ln (G′, G′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G′ greater than G′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.     

Semi‐dilute solutions of hydroxypropyl guar gum: Viscosity behaviour and thixotropic properties

Semi‐dilute solutions of hydroxypropyl guar gum (HPGG), the most widely used derivative of naturally occurring guar galactomannan, were investigated with respect to their viscosity, yield stress and thixotropy. It was found that the shear‐dependent viscosity behaviour under various HPGG concentrations, added salts and temperature could be well described by the Cross viscosity model. The zero‐shear‐rate viscosity was observed to change with HPGG concentration according to a power‐law function, and decease with the increase of temperature according to an Arrhenius‐type equation. The addition of salts (KCl and CaCl₂) lowered the zero‐shear‐rate viscosity. The HPGG solutions of high concentration showed a higher degree of thixotropy while the addition of salt lowered the thixotropic property. Copyright © 2007 Society of Chemical Industry     

RHEOLOGICAL BEHAVIOR OF POMEGRANATE (PUNICA GRANATUM L.) JUICE AND CONCENTRATE

The rheological behavior of pomegranate juice (Punica granatum L.), prepared from fresh pomegranates, was studied as a function of solids concentration in the range 17.5–75°Brix at 10–55C, using a controlled stress rheometer. Concentration methods did not influence flow behavior. There were no significant differences (P > 0.05) between viscosity and activation energy values for the pomegranate juices concentrated by different methods. The juices exhibited Newtonian behavior regardless of the concentration method. The effect of temperature was described by an Arrhenius‐type equation with an activation energy in the range 5.34–32.2 kJ/mol depending on concentration. An exponential model described better the effect of the soluble solids on the viscosity and E_avalues. A simple equation was proposed for describing the combined effect of temperature and soluble solids content on the juice viscosity.     

Studies on the steady shear flow behavior and functional properties of Lepidium perfoliatum seed gum

Flow properties of Lepidium perfoliatum gum, extracted from Qodume shahri seeds, as influences of concentrations (0.5%, 1%, 1.5% and 2%), temperatures (5, 25, 45, and 65 °C), salts and pHs were investigated. Among the selected models, power law model well described the rheological behavior of the L. perfoliatum seed mucilage solutions with high determination coefficients, R² and low root mean square error (RMSE). Non-Newtonian shear thinning behavior was observed at all temperatures and concentrations. While increase in temperature decreased the viscosity and increased the flow behavior indices, adverse effect was obtained by increasing the concentration. The temperature effect was more pronounced at 0.5% L. perfoliatum seed gum concentration and indicated the higher activation energy (E_a: 31614.56 J/mol). The viscosity was dependent on type of salt addition, and decreased with salt concentration. This behavior was more evident when using divalent salt. A marked dependence of viscosity on pH was also observed, as pH increased from acidic to alkaline conditions, the viscosity increased until pH of 9 and afterward decreased. The hydrocolloid showed good water absorption capacity (WAC) and imparted relatively high stability to foam and oil-in-water emulsion. However, the gum solubility was low at all temperatures studied (30, 60 and 90 °C).     

Steady and dynamic shear rheology of glutinous rice flour dispersions

The steady and dynamic shear rheological properties of Korean glutinous rice flour dispersions were evaluated at different concentrations (4, 5, 6, 7 and 8%). Glutinous rice flour dispersions at 25 °C showed a shear‐thinning behaviour (n = 0.487–0.522) with low magnitudes of Casson yield stresses (σ_oc = 0.056–0.339 Pa). The magnitudes of σ_oc, consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The power law model was found to be more suitable than the exponential model in expressing the relationship between concentration and apparent viscosity. The apparent viscosity over the temperature range of 25–70 °C obeyed the Arrhenius temperature relationship, with high determination coefficients (R² = 0.982–0.998), indicating that the magnitudes of activation energies (E_a) were in the range of 9.05–11.89 kJ mol^?1. A single equation, combining the effects of temperature and concentration on η_a,100, was used to describe the flow behaviour of glutinous rice flour dispersions. Magnitudes of storage (G′) and loss (G′′) moduli increased with the increase in concentration and frequency. Magnitudes of G′ were higher than those of G′′ over most of the frequency range.     

Degradation Kinetics of Myosin Heavy Chain of Pacific Whiting Surimi

Pacific whiting surimi paste was ohmically heated to investigate degradation of myosin heavy chain (MHC) caused by endogenous proteinase over a range of 40–85°C and 0.5–35 min. Degradation was best described with an apparent reaction order of 1.4. Changes of degradation rate increased with temperature and reached a maximum at 57°C. Then, rate of MHC degradation decreased with higher temperature and reached a minimum at 75°C. E_a values of activation and inactivation zone were 142.3 and 83.1 kJ/mol, respectively. Generally, failure shear stress and shear strain increased linearly with MHC content. Proteolytic degradation of actin exhibited the same trend as that of MHC but at a slower rate. The synergistic effect of actin in the gelation of whiting surimi was predominant at ≥75°C.     

Rheological Properties of Rice Starch Dispersions in Dimethyl Sulfoxide

The steady and dynamic shear rheological properties of rice starches dispersed in dimethyl sulfoxide (DMSO) solution (90% DMSO‐10% water) were evaluated at various concentrations (7, 8, 9 and 10%, w/w). Rice starch dispersions in DMSO solution at 25°C showed a shear‐thinning flow behavior (n=0.44–0.60) and their consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The apparent viscosity over the temperature range of 25–70°C obeyed the Arrhenius temperature relationship, indicating that the magnitudes of activation energy (E_a) were in the range of 11.7–12.7 kJ/mol. The Carreau model provided better fit on the shear rate‐apparent viscosity data than the Cross model. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of rice starch dispersions increased with the increase in concentration. G′′ showed a higher dependence on frequency (ω) compared to G′ due to the higher G′′ slopes. All rice starch dispersions showed the plateau of G′ at high frequencies. Intrinsic viscosity of rice starch dispersions in DMSO was 104.1 mL/g.     

COMPLEX VISCOSITY-TEMPERATURE MASTER CURVE OF CORNSTARCH DISPERSION DURING GELATINIZATION

Complex viscosity (η*) of 8% cornstarch dispersion during gelatinization at oscillatory frequencies (ω): 0.63–47.12 (rad s^?1) was independent of the heating rates: 1.6–6.0 (°C min^?1) when temperature was the independent variable. The influence of ω on η* was scaled by a frequency shift factor resulting in reduced complex viscosity (η*_R) versus temperature (60–95C) master curve. Similar η*_R master curves were derived for data on 6% and 3.5% dispersions. A modified Cox-Merz rule correlated the complex and apparent viscosity data, and a power law model described the effect of concentration of the gelatinized structures.     

Effect of Concentration and Temperature on the Rheological Properties of Oat Milk

The rheological behavior of oat milk (Avena sativa L.) at different concentration (5, 10, 15, and 20 °Brix) was studied in the temperature range of 10, 20, 30, and 40 °C using a controlled stress rheometer. Power law model adequately described the flow behavior of oat milk (0.881–0.987). The value of flow behavior index (n) was less than unity (0.19–0.68) at all temperature and concentration range indicating the shear-thinning (pseudoplastic) nature of oat milk. Consistency index (k) increased with soluble solids concentrations and decreased with temperature. The Arrhenius equation adequately described the effect of temperature on the viscosity. The activation energies for flow of oat milk quantified using Arrhenius equation increased with solid concentration and ranged from 7.43 to 303.64 kJ/mol. The effect of concentration on the viscosity followed the exponential model. The empirical model obtained from the study could well-describe the combined effect of temperature and concentration within the range of the study. It was concluded that temperature and concentration had a significant effect on the rheology of the oat milk.     

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.     

Rheological properties of Lepidium sativum seed extract as a function of concentration, temperature and time

The seeds of Lepidium sativum (Garden Cress) were selected as a new source of hydrocolloid and its chemical composition and molecular parameters were determined. The macromolecular component of the extract had a molecular weight of 540 kDa, and was nearly as rigid as xanthan with regard to chain conformation. The main rheological features were investigated as a function of shear rate, concentration and temperature. The extract exhibited strong shear-thinning behaviour, which was even more pronounced than for xanthan. An increase in concentration or temperature led to an increase in pseudoplasticity. The Arrhenius model was applied to the temperature dependence of viscosity, and the activation energy (E_a) was found to decrease with increasing concentration. The extract solutions showed thixotropic behaviour at all the concentrations and temperatures studied, and the first-order stress decay model with a non-zero equilibrium stress fairly described the time-dependent behaviour. The rheological characteristics found indicated a potential application of the extract as a novel thickener.     

Rheological behaviour of sago (Metroxylon sagu) starch paste

Rheological behaviour of gelatinized sago starch solution was studied over the shear rate range of 13.61–704 s⁻¹ at various concentration and temperature ranges. A power law equation was used to describe the rheological behaviour of the starch solution, while the effect of temperature was evaluated by the Arrhenius equation. The effect of starch concentration on apparent viscosity was studied using the exponential model describing the relationship between apparent viscosity and concentration. Consistency index (κ) increased with concentration and decreased with the increase of temperature. Flow behaviour indices (η) were within the range of 0.495–0.559 which indicated the pseudoplastic nature of gelatinized sago starch. The amount of starch and shear rate affect activation energy (ΔE). Depending on the shear rate and concentration, activation energy varied from 0.619 to 1.756 kcal mol⁻¹. A mathematical relationship correlating the various parameters (temperature, concentrations, shear rates) was tested for its significance and validity.     

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.     

Prediction of Vitamin C Retention of Potato Strips Blanched in Water

A model based on the mathematics of diffusion was developed to predict the retention of vitamin C of potato strips blanched in water. The vitamin C loss mechanism is by diffusion in unsteady state, considering the losses caused by enzymatic action or thermal degradation to be negligible. The apparent diffusion coefficient of vitamin C in potato is supposed to be constant with the concentration, and variable with the temperature according to equation D_a= D_a0 exp (? E_a/R_a T), in which Da₀ and E_a are experimental values different in the 25–65°C and 65–100°C temperature ranges. The model determines adimensional average temperatures and vitamin C average concentration as a function of blanching time, at 66, 77 and 88°C, in straight cut potato strips of 9.5 × 9.5 × 96, 11 × 11 × 96 and 13 × 13 × 96 mm, with heat transfer coefficients ∞, 1000 and 300 W/m²⁰C, respectively. The model was verified using published data.