Flow Properties of Solutions of Oat β-Glucans

The flow properties of aqueous solutions of oat β-glucans were studied using a Bohlin rheometer (concentric cylinder geometry) over the shear rate range 0.734–1500 1/sec at temperatures between 15 and 75 °C. The β-glucan powder concentrations employed were 0.20–1.56% (w/w). The power law model was satisfactory for describing the flow behavior of β-glucans over the shear rate range 18.6–232 1/sec. The magnitudes of activation energy were in the range 2.41–4.61 (kcal/ mol). Sucrose decreased the flow behavior index and increased the consistency index of β-glucans and decreased the activation energy at lower β-glucan concentrations, these effects being most pronounced at a sucrose concentration of 25%. The D-value for solutions of β-glucans (0.65%) at 100 °C was 145 hr.     

Steady state flow behaviours of extruded blend of rice flour and soy protein concentrate

Rheological properties in terms of steady state flow behaviours of extruded dispersions (rice flour/soy protein concentrate blend), were investigated using dynamic rheometry. The effects of concentration (2%, 5%, 7%, 9% and 11%) and temperature (25–70 °C) on the rheological parameters (yield stress, flow behaviour index) of the non-expanded pellet blend (12.5% protein) were determined using common rheological models. Steady-shear viscosities in a range of shear rate from 0 to 500 s⁻¹ were observed as a function of concentration and temperature. From typical curves showing the dependence of shear stress on shear rate, it could be observed that all suspensions exhibited a non-Newtonian and pseudoplastic behaviour. The model that best fitted the experimental data at all temperatures and concentrations was the Herschel–Bulkley model.     

Flow behaviour of inulin-enriched dairy desserts: influence of inulin average chain length

The effect of the addition of different types of inulin (long-chain, native and short-chain inulin) at four concentrations (0, 2.5, 5 and 7.5% w/w) on flow properties of semisolid dairy desserts formulated with either skimmed or whole milk and three modified tapioca starch concentrations (2.5, 3.25 and 4% w/w) was studied. All samples displayed shear-thinning flow behaviour. The addition of the three types of inulin to whole milk samples with low starch concentrations (2.5 and 3.25% w/w) led to combined hysteresis loops: samples showed antithixotropy at low shear rate values, but thixotropy at high shear rate values. The remaining samples showed thixotropic behaviour. The effect of the different types of inulin on the flow properties was not only highly dependent on the inulin concentration but also on milk type and starch concentration. On adding 7.5% of long-chain inulin, which significantly increased consistency index values and significantly decreased flow index values in both types of milk and for all starch concentrations.     

Study of the shear and extensional rheology of casein,waxy maize starch and their mixtures

This work investigated the shear and uniaxial extensional flow behaviour of aqueous casein and phosphated waxy maize starch systems as a function of the deformation rate, biopolymer concentration and the temperature. Trouton ratios were calculated to compare different responses of biopolymers to the shear and extensional deformation. It was found that the casein system (20% w/w) had a much higher and linearly increasing Trouton ratio against the log increase of strain rate. The starch system (35% w/w) had a Trouton ratio close to 3 at low strain rates, but increasing linearly once the strain rate exceeded 2 s⁻¹. The apparent shear and extensional viscosity showed an exponential increase with the concentration for both biopolymers, with casein being more concentration dependent. Their Trouton ratios were also very much concentration dependent: remained close to 3 at low biopolymer levels, but increased significantly at higher concentrations. Temperature variation experiments demonstrated that the flow properties of casein and waxy maize starch follow an Arrhenius relationship, with casein showing stronger temperature dependence than starch. While casein systems displayed a decrease in Trouton ratio with temperature increase, waxy maize starch had the opposite behaviour. The mixing of casein–waxy maize starch resulted in higher apparent extensional viscosities and higher Trouton ratios than single biopolymer systems.     

Rheological properties of selected hydrocolloids as a function of concentration and temperature

In this study, rheological properties of several food hydrocolloids (carrageenan, pectin, gelatin, starch and xanthan) were evaluated using a rotational viscometer at three concentrations (1–6%, depending on the type of hydrocolloid) and four temperatures (20, 40, 60 and 80°C). Samples were subjected to a programmed shear rate increasing linearly from 0 to 300 s⁻¹ in 3 min, followed by a steady shear at 300 s⁻¹ for 10 min and finally a linearly decreasing shear rate from 300 s⁻¹ to 0 in 3 min. Experiments were performed in duplicate. In general, the power law model fitted most of the experimental results. Xanthan gum and carrageenan (at 20^oC) were exceptions, characterized by a yield stress and hence the rheograms were fitted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonian behavior. Three models (power, exponential and polynomial) were used to evaluate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan showed the most temperature dependency and xanthan gum, the least.     

Heat‐induced gels of soy protein and κ‐carrageenan at different pH values

Heat‐induced (90 °C/30 min) gelling of soy protein isolate (SPI) and κ‐carrageenan (κ‐CR) systems at pH values of 6.7 and 5.7 was evaluated. κ‐CR addition, increase in protein concentration and reduction in pH led to decreases in the initial gel structure forming temperature. Self‐supporting gels were not formed at concentrations of 8% (w/w) SPI or at concentrations below 0.3% (w/w) κ‐CR, but an increase in the concentration of SPI and κ‐CR led to an increase in the stress at rupture without influencing the deformability. Gel properties were a consequence of a simultaneous process of gelling and phase separation during heating. The non‐linear parameter of the Blatz, Sharda and Tschoegl (BST) rheological model allowed for the evaluation of the structural characteristics that in general corresponded to strain hardening behaviour. Strain weakening behaviour was observed at high biopolymer concentrations and at pH 6.7, which was associated with accentuated phase separation and a more discontinuous gel network.     

Rheology of Okenia hypogaea Starch Dispersions in Aqueous Solution of DMSO

The aim of this work was to study the rheological behavior of Okenia hypogea starch dispersions (OSD) in aqueous solution (90/10, v/v) of dimethyl sulfoxide (DMSO). Okenia starch dispersions with 3 and 7 % (w/v) total solids were prepared at 20 °C and rheological tests were undertaken at 20, 40 and 60 °C, using a shear rate controlled rotational viscometer. The data fitted better the power law than the Casson model. Flow curves and flow behavior index indicated shear‐thinning behavior. All rheological parameters were affected by the solids concentration and the measurement temperature. As regards amylose and amylopectin content okenia starch is grouped among “ordinary” (non‐waxy) starches. Overall, OSD behaved similarly to potato starch dispersions and corn starch dispersions used as controls.     

Flow behavior and functional properties of barley and oat water‐soluble β‐D‐glucan rich extractions

Flow characteristics and functional properties of water‐soluble β‐glucan rich extractions prepared from hulled barley, hulless barley and oats were investigated. Rheological behavior was studied using a coaxial viscometer over shear rates of 3.0‐ 1312s^?1. The shear rate‐shear stress data followed the power law and Herschel‐Bulkley models. The flow behaviour index values varied from 0.31‐0.97, indicating mildly to highly pseudoplastic nature of the aqueous solutions of β‐glucan rich extractions. The pseudoplasticity for the aqueous solutions increased with increasing concentration of extractions. The hulless barley β‐glucan rich extractions showed higher pseudoplasticity, consistency index, and yield stress values; absorbed less water and exhibited higher fat absorption and oil emulsifying properties than those of the hulled barley and oats. There was no discernible influence of fat contents on functional properties of the concentrates. Dough development time, arrival time, stability and softening of the dough were negligibly affected with addition of various β‐glucan rich extractions to the flours. Supplementation of β‐glucan rich extractions desirably increased the baking absorption of the flours. Bread with improved loaf quality could be obtained using various β‐glucan rich extractions upto a level of 1.00% (w/w), especially, from those of hulless barley cv. PNB 5.     

番茄汁液流变性质的关联

对经45、32、24和16目筛网过筛所得番茄汁液的流变性质进行了研究。采用旋转式粘度计测定了番茄汁的剪切速率-剪应力数据。通过剪切速率-剪应力实验数据的关联发现,番茄汁液的流变行为可用Bingham模型表征。确定了不同温度和不同网目下番茄汁液的稠度指数和屈服应力。同时也建立了不同网目下番茄汁液的表观粘度与温度函数关系的关联式。     

Rheology of scleroglucan dispersions

The rheological properties of a scleroglucan, industrially produced by Sclerotium rolfsii, either in aqueous or dimethylsulfoxide (DMSO) dispersions at concentrations (c) ranging from 0.01% to 1.5% (w/w) were determined by using Cannon–Fenske capillary viscometers and a dynamic stress rheometer with plate-and-cone geometry under steady shear flow, small amplitude oscillatory shear and creep. The intrinsic viscosity [η] in water and DMSO was found to be equal to 12.1±0.3 and 4.6±0.3 dl/g, respectively. Despite the creep and oscillatory tests pointed out the presence of more or less strong molecular entanglements resulting in a three-dimensional network for c0.35% (w/w), the steady shear flow ones using a stress increasing exponentially with time showed a Newtonian behaviour at low enough shear rates, a pseudo-plastic one in the middle shear rate range and a second Newtonian plateau at very high shear rates. The Cross equation was capable of describing the rheological behaviour of the aqueous scleroglucan dispersions both in the sol and gel domain for shear rates and scleroglucan concentrations in the ranges 5×10⁻⁵–3.5×10³ s⁻¹ and 0.15–1.5% (w/w), respectively; while the Ostwäld-de-Waele model well fitted the apparent viscosity of the scleroglucan dispersion in DMSO at c=1% (w/v) and ranging from 2.5 to 180 s⁻¹.     

Flow behaviour of inulin–milk beverages. Influence of inulin average chain length and of milk fat content

The effects of the addition of different types of inulin (oligofructose, native and long chain) at different concentrations (2%, 4%, 6%, 8% and 10%, w/w) on the flow behaviour of milk beverages model systems were studied. The flow of the inulin–milk solutions was Newtonian, except for whole milk samples with higher long chain inulin concentrations (8% and 10%), which were shear thinning. All inulin-κ-carrageenan–milk samples were shear thinning. The viscosity of 3.1% fat whole milk could be approximated by skim milk with 4–10% short chain inulin, or with 6–8% native inulin or with 4–6% long chain inulin. In κ-carrageenan–milk samples the addition of inulin could not replace the effect of milk fat on the viscosity of these systems.     

Effect of addition of sucrose and aspartame on the compression resistance of hydrocolloids gels

The effect of adding sucrose (5–25% w/w) and aspartame (0.04–0.16% w/w) on the compression resistance of three hydrocolloid gelled systems: κ‐carrageenan, gellan gum and κ‐carrageenan/locust bean gum at three different concentrations (0.3, 0.75 and 1.2% w/w) was studied. Sucrose addition increased true rupture stress in the three‐gelled systems, this effect being stronger in gellan gels. The deformability modulus increased with sucrose concentration in gellan gels, but not in the other systems. Rupture stress and deformability modulus increased with the addition of sucrose only in the harder gels (0.75 and 1.2% w/w). The effect of sucrose addition on the true rupture strain was significant but, in general, not important, mainly for lower gum concentrations. Aspartame addition did not affect the compression parameters.     

Rheological Characterization of Skim Milk Stabilized with Carrageenan at High Temperatures

ABSTRACT: Superpositioning principles were applied twice to model temperature (25 to 125 °C) and concentration (0.005 to 0.040% w/w) effects on skim milk and carrageenan solutions. Samples were analyzed using a controlled stress rheometer equipped with a pressurized sealed cell, permitting measurements well above standard boiling conditions. Individual samples were sheared between 10 and 160 s⁻¹, and predictive equations were developed to predict Newtonian viscosity as a function of temperature and carrageenan concentration. The superpositioning technique coupled with advancements in rheological instrumentation permits high temperature measurements and offers a strategy for viscosity determination for thermal processing unit operations.     

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 and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins

Ambarella and mango peels are good sources of pectins (15–20%), with high degree of methylation (60–78%) and high molar masses. Ambarella and mango ( Améliorée and Mango varieties) peel pectins were extracted using HCl or oxalic acid/ammonium oxalate (OAAO). Purified pectins were analysed for their flow behaviour and phase diagrams were established at pH 3 as sucrose vs. pectin concentration. The gelation kinetics and mechanical spectra of these pectin gels were studied and compared to those of commercial citrus (lime) pectins. At a concentration of 1% (w/v), all pectic solutions had a shear thinning behaviour but at 0.6% (w/v), only OAAO-extracted pectins exhibited such behaviour. Phase diagrams showed that at pH 3, gelation of OAAO mango extracted pectins was possible at low polymer concentration (0.2%; w/w) for a sucrose concentration of 60% (w/w). OAAO-extracted pectins exhibited a higher gelling ability than HCl-extracted ones. Sucrose (45–50%) and pectin (0.2–0.6%) concentration had a deep impact on the gel strength. Our results enable to conclude that the OAAO extraction from mango and ambarella peels allowed the recovery of pectins that exhibit high gelling properties.     

Effects of concentration and temperature on carboxymethylcellulose rheology

The rheological properties of 0.5 to 2.0% carboxymethycellulose (CMC) solutions were measured at 30–90°C with a computer controlled rotational viscometer in a linearly increasing and decreasing three-cycle shearing sequence. CMC solutions showed power-law flow behaviour and rheological properties were significantly ( P < 0.01) influenced by both temperature and concentration. an empirical model was developed to relate the power-law parameters to both concentration and temperature.     

Elongational flow studies of set yogurt

Three series of prepared set yogurt samples were tested using squeezing flow viscometry. Samples were compressed using an Instron UTM at constant deformation rate. The first series containing added caseinates exhibited deformation behaviour of a gel. Firmness was dependent on caseinate concentration. The second series contained skimmed milk powder. Their behaviour was more that of a colloidal dispersion at low added powder content and of a gel at higher added amounts. The third series contained carrageenan salts. Their behaviour was that of a dispersion irrespective of the carrageenan concentration. The consistency of the samples examined was evaluated using plots of stress growth coefficients as function of biaxial strain rate. The results indicated that the technique could be used to distinguish changes in yogurt structure caused by the addition of various additives at various concentration levels, to milk to enhance yogurt consistency.     

Steady and dynamic shear rheological properties of extrusion modified fenugreek gum solutions

This study investigated the rheological properties of extrusion modified fenugreek gum solutions (0.5, 1.0, 1.5, and 2.0%, w/v) under steady and dynamic shear conditions. Fenugreek gum was extruded in a twin-screw extruder without an exit die to minimize a decrease in molecular weight of fenugreek gum during extrusion process. Both of the steady and dynamic shear rheological tests revealed that extrusion process did not substantially influence the steady and dynamic shear properties of the gum. The power law model was applied to describe the flow behavior of the extruded gum solutions. The extrusion modified fenugreek gum solutions exhibited a shearthinning flow behavior at 25°C, and the values of consistency index (K) and apparent viscosity (η_a,100) increased with an increase in the gum concentration. The magnitudes of storage modulus (G′) and loss modulus (G″) for the extrusion modified fenugreek gum solutions increased with increasing frequency (ω) and with increasing gum concentration.     

APPLICATION OF AN IN-LINE RHEOLOGICAL CHARACTERIZATION METHOD TO CHEMICALLY MODIFIED AND NATIVE CORN STARCH

The application of an in‐line ultrasonics‐based rheological characterization method for measuring the rheological properties of 6% (w/v) acid‐thinned and native corn starch suspensions and gels was studied. The measurements were performed in steady, laminar pipe flow using a 5 MHz frequency transducer to determine the radial shear rate distribution. Two pressure transducers were used to measure the pressure drop allowing the shear stress distribution to be calculated through the conservation of linear momentum. It was possible to obtain shear viscosity over a range of shear rates, 1–50 1/s, from a single velocity profile. A comparison of the shear viscosity function at different flow rates showed that this method could be a valid method of process rheometry during the manufacturing of starch‐based products. Both ultrasonics and rotational rheometry results showed that acid‐thinned and native corn starch suspensions exhibited Newtonian behavior before heat treatment and non‐Newtonian behavior after heating. Power law consistency index and flow behavior index of the acid‐thinned corn starch gel at 39°C were 0.60 Pa.s ^0.68 and 0.68, respectively; whereas those of the native corn starch were 5.90 Pa.s ^0.37 and 0.37 at 38C. Their consistency index increased and flow behavior index decreased with cooling and a thermoreversible change in the flow behavior index was observed in the native corn starch after storage.     

LINEAR AND NONLINEAR VISCOELASTIC BEHAVIOR OF OIL-IN-WATER EMULSIONS STABILIZED WITH POLYSACCHARIDES

The rheological behavior and stability of oil-in-water emulsions stabilized by different thickening agents were analyzed. Food emulsions were prepared with commercial sunflower oil (40% w/w oil-in-water) and stabilized with 1% emulsifier. The tested thickeners were: (1) 1% w/w xanthan gum (XG), (2) 5% w/w potato starch (PS), (3) 5% PS + 0.5% XG, (4) 1% w/w guar gum (GG), and (5) 0.5% XG + 0.5% GG. Mean droplet size and droplet size distribution (DSD) of emulsions were determined by static light scattering. Steady flow (viscosity versus shear rate), transient flow (viscosity versus time) and oscillatory shear tests (linear viscoelasticity) were performed. The addition of thickening agents improved the stability of the emulsions, the effect was less marked in systems containing only GG. DSD was not significantly modified in emulsions containing starch or hydrocolloids. Microscopic observations showed that all the tested emulsions were flocculated due to the presence of hydrocolloids. The observed shear thinning behavior was attributed to the molecular structure of the polysaccharides and to the flocculation/deflocculation process; viscosity data were satisfactorily fitted to the Cross model. Frequency sweeps showed that emulsions with PS or XG have a weak gel structural network (G' > G); those with GG correspond to a polymeric solution where G' and G" curves intersect within the range of tested frequencies. The viscoelastic linear behavior was described according to the Maxwell generalized model. The discrete relaxation spectrum and relaxation times were estimated from the experimental values of G' and G" for emulsions with PS, PS + XG, and XG. Nonlinear viscoelasticity was also studied from stress relaxation curves at different shear strains. The damping function was calculated and the Soskey-Winter parameters were determined. Transient flow viscosities at different shear rates were comparable to the values estimated from stress relaxation measurements.