Steady Shear Rheological Properties Research Articles

Physicochemical, Hydration and Steady Shear Rheological Properties of Flours Derived From Different Crop Residues From the Honduran Agro–Food Industry

This study aimed to determine the physicochemical, hydration, and rheological characteristics of flours derived from different crop residues (taro, cassava, maize, and banana) affected by climate change in Honduras and to investigate their potential application in food processes. The physicochemical (moisture content, ash, protein, crude fat, starch, amylose content, and color), hydration (water absorption capacity (WAC), water absorption index (WAI), water solubility index (WSI), swelling power (SP), true and bulk density), pasting (pasting temperature, peak, trough, breakdown, setback, and final viscosity), and rheological properties of the flours were evaluated. Taro flour had the highest values of ash content, WAI and SP and the lowest for crude fat, amylose content, bulk density and peak, breakdown, setback viscosity and consistency index. Cassava flour had the highest breakdown viscosity and flow behavior index values and the lowest for protein content, hysteresis loop area, yield stress, and consistency index. Maize flour had the highest crude fat, protein, and amylose content, bulk density, WAC, setback viscosity, hysteresis loop area, and yield stress, and the lowest values were for ash, protein content, WSI, pasting temperature, breakdown viscosity, and flow behavior index. Banana flour had the highest starch, carbohydrate, WSI, pasting temperature, peak viscosity and consistency index, and the lowest value for protein content, WAI and SP. The study's results have determined the compositional value and functionality of the flours obtained from the agro-residues studied for their potential use in different food products. Keywords: Crop residues flour; Food security; Change climatic; physicochemical characterization; steady shear

Rheological characteristics of concentrated ternary gum mixtures with xanthan gum, guar gum, and carboxymethyl cellulose: Effect of NaCl, sucrose, pH, and temperature

Our goal was to investigate the effects of various conditions of media (NaCl, sucrose, pH, and temperature) on the steady and dynamic shear rheological properties of a concentrated ternary gum mixture system (1.0 wt%) containing xanthan gum (XG), guar gum (GG), and carboxymethyl cellulose (CMC). Regardless of the media conditions, all gum mixtures exhibited a high shear-thinning behavior with a low flow behavior index (<0.30). NaCl addition resulted in a decrease in the consistency index (K, 32.8–16.1 Pa·sn) and apparent viscosity at 50 s−1 (ηa,50, 1.00–0.75 Pa·s), as well as the elastic modulus (G′) and viscous modulus (G″) due to the charge screening effect. Similar result was observed with an increase in acidity of media. The presence of sucrose also induced the decrease in the ηa,50, K, G′, and G″ values of the ternary gum, but tan δ (G″/G′) decreased, indicative of higher weak gel-like properties. No effect of NaCl or sucrose addition on the temperature dependence of G′ values was observed, whereas pH adjustment was impacted. These results demonstrated that the presence of co-solute, the acidity of media, and temperature influenced the rheological properties of ternary gum, and in particular acid condition gave a great impact.

Steady shear rheological properties, microstructure and stability of water in water emulsions made with basil seed gum and waxy corn starch or high pressure-treated waxy corn starch

The water in water (W/W) emulsions were prepared by mixing basil seed gum (BSG) with waxy corn starch (WCS) or high pressure-treated waxy corn starch (HWCS) at different concentrations. Increasing the concentration of WCS or HWCS increased the zeta potential, consistency index, infinite shear viscosity, and apparent viscosity, while it decreased the Z-average droplet size, polydispersity index, separation index, and flow behavior index of the W/W emulsions. After increasing the concentration of WCS and HWCS, the micrographs captured by an optical microscope indicated that the number of follicular droplets increased more than individual droplets. However, coalescence did not occur due to electrostatic repulsion. When the concentration of WCS and HWCS was increased from 0.5 to 2 wt% (at a constant concentration of 0.25 wt% and 0.2 wt% of BSG, respectively), the consistency index of the emulsions was increased significantly (p < 0.05) from 0.109 to 0.436 Pa. sn and from 0.032 to 0.743 Pa. sn, respectively. The results simply revealed the capability of 0.2 wt% BSG+ 0.5, 1, or 2 wt% HWCS and 0.25 wt% BSG+ 0.5, 1, or 2 wt% WCS for being utilized as stable W/W emulsions; these emulsions were stable for at least a week.

Camel milk-sweet potato starch gel: steady shear and dynamic rheological properties

Camel milk is known to produce low quality gels. To address this drawback, sweet potato starch (SP), camel milk (CM), or cow milk (CWM) were blended and cooked in alkaline conditions. The rheological tests of the prepared gel were done using DHR- Hybrid Rheometer. Because the G’ was, by far, larger than G”, the prepared gel exhibited viscoelastic behaviour as well as shear thinning. The gel exhibited tan δ < 1.0 which indicates solid-like material, but obvious variances between the gels were detected. The gels prepared from CM were harder than CWM, but it was frequency-dependent at low frequencies from 0.1 to 1.0 (rad/sec). Samples containing camel milk presented stronger structure due to the low power law exponent (n), while CWM showed more shear thinning. The obvious high G’ and the low (n) value is projected to have processing repercussions on CM gel.

The Effect of Cold Press Chia Seed Oil By-Products on the Rheological, Microstructural, Thermal, and Sensory Properties of Low-Fat Ice Cream.

This study aimed to investigate the utilization of cold-pressed chia-seed oil by-products (CSOB) in a low-fat ice cream formulation as a fat replacer and stabilizer. In the study, ice cream emulsion mixtures were formulated by using 0.2–0.4% xanthan gum (XG), 2.5–12.5% fat, and 1–3% CSOB. Optimization was performed using the response surface methodology (RSM) and full factorial central composite design (CCD) based on the flow behavior rheological properties of the emulsions obtained from 17 different experimental points. All of the emulsion samples showed non-Newtonian shear-thinning flow behavior. The consistency coefficient (Κ) values of the emulsion samples were found to be 4.01–26.05 Pasn and were significantly affected by optimization parameters (p < 0.05). The optimum formulation was determined as 0.29% XG, 2.5% CSOB, 2.5% fat. The low-fat (LF-IC) and full-fat control samples (FF-IC) were compared to samples produced with an optimum formulation (CBLF-IC) based on the steady shear, frequency sweep, and 3-ITT (three interval thixotropy test) rheological properties, thermal properties, emulsion stability, light microscope images, and sensory quality. CBLF-IC showed similar rheological behavior to FF-IC. The mix of CBLF-IC showed higher emulsion stability and lower poly-dispersity index (PDI) value and fat globule diameters than those of FF-IC and LF-IC. The thermal properties of the samples were significantly affected by the addition of CSOB in an ice cream mix. CBLF-IC exhibited a lower temperature range (ΔT), enthalpy of fusion (ΔHf), and freezing point temperature (Tf) than those of FF-IC and LF-IC. While CBLF-IC exhibited a higher overrun value than other samples, it showed similar sensory properties to the FF-IC sample. The results of this study suggested that CSOB could be used successfully in low-fat ice cream production. This study also has the potential to gain new perspectives for the evaluation of CSOB as a fat substitute in a low-fat ice cream.

Barnyard millet starch cross-linked at varying levels by sodium trimetaphosphate (STMP): Film forming, physico-chemical, pasting and thermal properties

Sodium trimetaphosphate (STMP) at different levels (1, 3 and 5%) was used to prepare cross-linked (CL) barnyard millet starch. The starches were studied for their physicochemical, pasting, steady shear rheological and thermal properties. Further, films were formulated from these starches and assessed for their functional and mechanical behavior. Amylose content of native starch (15%) decreased upon cross-linking (7.86–9.65%). CL starches had lower swelling power (SP) and solubility than native starch. CL starches showed lower peak (7049–9649 mPa.s), breakdown viscosities (BV) (1073–3172 mPa.s) but higher pasting temperature (PT) (79.7–80.8 °C) than native starch. Pasting properties were more affected for CL (5%) starch. Steady shear properties revealed lower yield stress (σo) values of CL starch pastes (1.39–2.37 Pa) than native starch paste (15.40 Pa). Flow behavior index was <1 for native and CL starches, thereby indicating their shear thinning behavior. Cross-linking increased gelatinization temperature, but decreased the enthalpy of gelatinization (ΔHgel) values. CL starch films exhibited lower water vapor permeability (WVP) and higher tensile strength (TS) and solubility than native starch films. CL (5%) starch film exhibited the lowest WVP (1.28 g.m/Pa.s.m2) and the highest TS (13.12 MPa) among films.

Development of Viscosified Acid-Surfactant Solutions for Oilfield Applications: Rheological Properties

Abstract Viscosified acids are desired in several oilfield applications such as in acid diversion and acid fracturing operations. The study aimed to delineate the rheological properties of a novel amine type surfactant and viscosified acid-surfactant solutions. The steady shear and dynamic rheological properties were evaluated by varying the surfactant, acid, and salt concentration. Such a study is required to gauge the suitability of the viscosifying agent in acid stimulation jobs. The surfactant solutions without acid showed shear-thinning behavior, whereas those with acid showed a Newtonian plateau over a wide shear rate range before undergoing shear thinning. This means that over a wide shear rate range, the acid-surfactant solutions become independent of applied shear. At low shear rates, the viscosity of the surfactant was higher compared with the surfactant-acid solution. However, at high shear rates, the viscosity of the surfactant was lower compared with the viscosity of the surfactant-acid solution. There was an optimal salt concentration that improved the viscosity and elasticity of the acid-surfactant solutions. Thus, the rheology of the surfactant solution can be improved by adding both acid and salt. The elastic properties of acid-surfactant solutions were also better compared with the elastic properties of pure surfactant. The addition of acid improved the elastic properties of the surfactant solutions. Constant viscosity over a range of shear rate is a suitable application for acid fracturing operations in which the acid leak-off will be minimal due to the high viscosity. Also, brines in most of the carbonate formation consist of high loading of calcium chloride which was found to have a positive effect on the viscosity. Increasing the calcium chloride leads to an increase in viscosity, and then subsequently decreases the viscosity. This shows that the acid and salt concentration plays a role in modifying the rheological properties of the surfactant solutions.

Rheological properties of a neutral polysaccharide extracted from maca (Lepidium meyenii Walp.) roots with prebiotic and anti-inflammatory activities

The rheological, prebiotic, and anti-inflammatory properties of neutral polysaccharide extracted from maca roots (MP) were investigated. MP was composed of arabinose, galactose, rhamnose, and glucose. In steady shear rheological properties, an increasing concentration of MP solution exhibited higher apparent viscosity (ηa,100) and consistency index (K) under acidic condition (pH 4). In dynamic rheological properties, the dynamic moduli (G′ and G″) in the frequency sweep test from the MP solution were increased with increasing concentration and decreasing pH. The changes in dynamic moduli of the MP solution with various concentrations and pH values were stable during 1 h storage at 4 °C due to the enhancement of hydrogen bonding. According to the results of the temperature sweep test, an increasing concentration of MP solution increased dynamic moduli under acidic conditions. The prebiotic properties of MP induced a higher growth of Bifidobacterium longum ATCC15707 and Lactobacillus rhamnosus ATCC 7469 than inulin and increased acetic acid, propionic acid, and butyric acid more than inulin in vitro. Furthermore, MP inhibited lipopolysaccharide-induced NO production in RAW 264.7 cells, which indicated that an increasing concentration of MP enhanced anti-inflammatory activities. Therefore, MP is a potential functional material for the food and pharmaceutical industries.

Effect of structure development on the rheological properties of PVDF/HNBR‐based thermoplastic elastomer and its vulcanizates

ABSTRACTThe present work demonstrates the structure‐rheology relationship of novel polyvinylidene fluoride/hydrogenated nitrile rubber blends with special reference to the effect of mixing time, which has not been amply discussed in the literature. In between 50 and 70 wt% rubber content, a yield in complex viscosity and secondary plateau in storage modulus were discerned due to interconnected droplets‐matrix morphology manifesting the thermoplastic elastomeric nature of the blends (TPEs). Such network‐like structure altered the rheological properties like relaxation time, capillary viscosity, die swell, elastic responses of the TPE with respect to the trend as expected according to the rule of mixing. Interestingly, in the early stages of mixing, when the dispersed size was bigger, the effect of physical network on the rheological properties was suppressed. During dynamic vulcanization (TPV), both lower and higher frequency responses in oscillatory shear flow, steady shear rheological properties, recoverable strain etc. have changed notably with mixing time. For example, although the complex viscosity of the TPV was higher at a lower frequency as compared to its TPE, it was significantly lower at a higher frequency at the beginning of dynamic curing; however, viscosity increased appreciably with time. Temperature‐dependendent rheological properties were also influenced with mixing time of the compositions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48758.

Controlling the rheological properties of wheat starch gels using Lepidium perfoliatum seed gum in steady and dynamic shear

In the present work, the influence of Lepidium perfoliatum seed gum (LPSG) addition in varied concentrations (0%, 0.25%, 0.5%, 0.75% and 1%, w/w) on dynamic and steady shear rheological properties of wheat starch dispersion (4%, /w) was examined. Comparison of the values of dynamic (G′, G″, τy, τf, tan δ), shear-dependent (ηa,50, η0, η∞, τ, m) and time-dependent (ηa,3s, k, η0, η∞) rheological parameters of the WS-LPSG mixtures with WS alone, indicated that the viscoelastic and flow properties of the mixtures were greatly affected by the addition of LPSG. According to the standard method provided by the National Dysphagia Diet (NDD), the WS and WS-LPSG gels were placed in the category of nectar-like (WS), honey-like (WS-0.25%LPSG, WS-0.5%LPSG and WS-0.75%LPSG) and spoon-thick (WS-1%LPSG) viscosity. In the simulated oral condition (SOC), the presence of saliva caused the increase of k value (10–81%), whilst decreased the values of η0 (43–95%) and η∞ (68–96%). As the concentration of LPSG increased, less decrease in value of ηa,3s in the SOC was observed. The results of present study demonstrated the feasibility of manipulating the viscosity of the WS gels by addition of LPSG to be suitable for the individuals with varying degrees of swallowing difficulty.

Structural characterization and rheological properties of the water extracted mucilage of Basella alba and the starch/aqueous mucilage blends

Basella alba is a succulent plant, and its stem and leaf contain significant amount of mucilage. However, researches about Basella alba mucilage are quite limited. Therefore, the objective of this study is to characterize the structural and rheological properties of the water extracted mucilage from the leaf and stem of Basella alba, including chemical compositions, monosaccharide compositions, intrinsic viscosity, molecular size distribution, and steady shear and dynamic shear rheological properties. Furthermore, rheological properties of starch/aqueous mucilage blends with various mixing ratio were also characterized. Results showed that the mucilage of Basella alba was comprised of 38–39 molar% of galactose, 28–36% of arabinose, 4–11% of galacturonic acid, and 3–5% rhamnose, with a weight average molecular weight of about 1.9-2.4 × 106. The intrinsic viscosity of leaf and stem mucilage solutions were found to be 2.48 and 9.20 dl/g, respectively. 2–6% of mucilage solutions showed slight shear thinning behavior, with a flow behavior index in the range of 0.58–0.85. Dynamic shear results revealed that 2–6% of mucilage solutions showed significant fluid properties, with a loss tangent value in the range of 1.1–3.4. However, as mixing with wheat starch under various proportions, significant synergistic effect was observed, particularly for the starch/aqueous mucilage ratio of 1.8/0.2 or 1.7/0.3, as evidenced by a significant increase in viscosity, storage modulus, and decrease in loss tangent to lower than one (0.2–0.3). On the contrary, no synergistic gelation occurred when adding mucilage to tapioca starch solutions. Gelation was even suppressed when adding mucilage to potato starch solutions. This discrepancy may be related to the differences in the nature of different starches. These information would be useful for future application.

Dynamic mechanical spectra of salep and casein mixtures.

In this study, a glucomannan based salep and casein were mixed in a solution at different concentrations (0-0.75% salep and 0-3.0% casein) according to the central composite rotatable design and their color, steady shear and dynamic shear rheological properties were characterized. All studied parameters were affected by the salep and casein levels significantly. Salep increased the apparent viscosity, consistency coefficient, storage modulus and complex modulus of the solution compared to casein and an interaction was observed between the salep and casein which shows a significant increasing effect on the parameters. Frequency dependency increased with the increase of casein in the mixtures. Regression equations having quite high coefficients of determination were constructed for the estimation of studied parameter levels. Optimization performed with desirability function showed that the maximum levels for the rheological parameters could be achieved by more increment of salep level in the solutions because sole effect of casein on the rheological parameters was limited compared to salep.

Oscillatory and steady shear rheological properties of aqueous polyacrylamide solutions

Abstract Dynamic and steady shear data representing the flow behaviour of aqueous solutions of Polyacrylamide, in the concentration range of 0.25–0.6% wt./vol. and temperature range of 5–45 °C, have been reported. Maxwell model, Carreau model and power law model were used to represent the present experimental data. Rheological parameter such as fluid relaxation time (λ), representative of fluid elasticity, was evaluated by fitting the oscillatory shear data to the four element Maxwell model. Other rheological parameters such as flow behaviour index (n) and flow consistency index (K) were evaluated by fitting the steady shear data to the power law model in the relevant shear rate range. The shear dependent viscosity data are well represented by Carreau model. Predictive equations for λ, n and K are proposed by incorporating the combined effect of temperature and concentration. Presented data could be of great use in various engineering applications such as enhanced oil recovery.

Hydrocolloid clustering based on their rheological properties.

In this study, we proposed an objective classification of seven commercial hydrocolloids and four novel hydrocolloids. Total of 74 rheological parameters was generated by steady (flow behavior, hysteresis loop, single shear decay, in-shear structural recovery experiments), dynamic (strain sweep and frequency sweep tests), and transient (creep/recovery and stress relaxation) shear measurements. Subsequently, the parameters were classified into seven categories with more than 60% similarity indexes in each group using agglomerative hierarchical clustering based on those properties related to the number of linkage, strength of linkage, distance of linkage, rupture and flow, rate of destruction, the extent of destruction, and the state of destructured samples in the absence of flow field. Fuzzy c-means classifier used to extract patterns for each class. Our results correspond to four different classes; κ-carrageenan and agar gum were categorized in the first class, high methoxyl pectin, xanthan, sage seed gum and basil seed gum in the second class, alginate gum and Balangu-Shirazi seed gum in the third class, and guar gum, cress seed gum and carboxymethyl cellulose in the fourth class. Using this classification technique, complete rheological patterns can be extracted for each class. This classification provides a map for other researchers to rationally design the best test type which could describe adequately different properties of materials and avoid experiments with a similar type of parameters. The main reason for the frequent use of hydrocolloids in various industries is their ability to modify the rheology. A lot of works have been done to study the rheological behavior of many hydrocolloids in model and food systems. As there is still demand for new sources of hydrocolloids with more specific functionality in foods, probing the similarities among commercial and emerging hydrocolloids could help us to rationally design structural features in different formulations, besides gives insight into the structure-function relationship between them. This object could be attained by clustering, a part of the pattern recognition theory. Contrary to the traditional clustering methods, in which the membership of a product is exclusive for only a class, in constraint clustering by fuzzy logic methods, a partial membership can be shared by two or more classes. In this way, using the fuzzy logic clustering method, we clustered a number of commercial and novel hydrocolloids based on the steady, transient, and dynamic shear rheological properties and found a specific pattern among them. PRACTICAL APPLICATIONS: The main reason for the frequent use of hydrocolloids in various industries is their ability to modify the rheology. A lot of works have been done to study the rheological behavior of many hydrocolloids in model and food systems. As there is still demand for new sources of hydrocolloids with more specific functionality in foods, probing the similarities among commercial and emerging hydrocolloids could help us to rationally design structural features in different formulations, besides gives insight into the structure-function relationship between them. This object could be attained by clustering, a part of the pattern recognition theory. Contrary to the traditional clustering methods, in which the membership of a product is exclusive for only a class, in constraint clustering by fuzzy logic methods, a partial membership can be shared by two or more classes. In this way, using the fuzzy logic clustering method, we clustered a number of commercial and novel hydrocolloids based on the steady, transient, and dynamic shear rheological properties and found a specific pattern among them.

Modeling the rheological properties of currant paste as a function of plasticizers concentration, storage temperature and time and process temperature

The steady and dynamic shear rheological properties of currant paste samples as a function of storage temperature (15, 25 and 35 °C) and time (180 days) and plasticizers content (water and/or glycerol) have been evaluated. Apparent viscosity (ηa) has been found to be significantly increased with prolonged storage, implying possible structural changes, and decreased with the increase in storage temperature and the addition of water or/and glycerol. Flow behavior index and consistency index were determined by fitting the resulting experimental data to a power law equation with high values of correlation coefficients (R2 ≥ 0.912). Furthermore, the combined effect of storage temperature, time and plasticizers concentration on the apparent viscosity was described adequately by a proposed empirical model, with low standard relative errors (SRE ≤ 0.011). Additionally, the viscoelastic properties were significantly affected by all evaluated parameters in the same way as in apparent viscosity while both moduli (G′ and G″) were modeled sufficiently (R2 ≥ 0.884) as power functions of oscillatory frequency. The heat treatment (heating from 25 to 100 °C and cooling back with a rate of 10 °C/min) applied has proved sufficient to reverse the observed storage effects. Moreover, the modified Cox-Merz rule was satisfactorily applied to describe the correlation between the apparent viscosity and the complex viscosity.

Effect of Tara Gum Addition on Steady and Dynamic Shear Rheological Properties of Rice Starch Isolated from the Korean Rice Variety 'Boramchan'.

The present study was performed to investigate the influence of tara gum (TG) addition on the steady and dynamic shear rheological properties of rice starch (RS) isolated from the Korean rice variety ‘Boramchan’ flour. From X-ray diffraction and Fourier transform infrared spectra of RS, it was found that RS was purely isolated. All RS+TG pastes (4.7:0.3, 4.5:0.5, and 4.3:0.7, w/w) showed shear-thinning fluid characteristics. Adding TG significantly increased the values of apparent viscosity and consistency index of RS. In the dynamic shear rheological analysis, the dynamic moduli and complex viscosity of RS+TG pastes were significantly greater than those of the RS paste, indicating that RS+TG pastes had significantly higher viscoelastic properties than the RS paste. Light microscopy images of RS+TG pastes showed that the addition of TG can inhibit the RS granule from swelling.

Effect of CMC addition on steady and dynamic shear rheological properties of binary systems of xanthan gum and guar gum

The effect of CMC on the steady and dynamic shear rheological properties of binary mixtures of XG and GG was examined at different mixing ratios. All XG-GG-CMC ternary mixtures had high shear-thinning behavior and the n value of the sample with 5% CMC was the smallest compared with those of other samples. A marked increase in K and ηa,50 values was observed for ternary mixtures at a lower content (5%) of CMC, indicating that the synergistic interactions of the XG-GG binary mixture were affected by the content of CMC. The effect of temperature on the ηa,50 was well described by the Arrhenius equation for all samples. The activation energy values of all ternary gum mixtures are higher than that of binary gum mixture, and these values also decreased with an increase in CMC content from 5 to 15%. The dynamic moduli of ternary gum mixtures decreased with an increase in CMC content. The tan δ value of the ternary gum mixture with 5% CMC was much lower than those of other ternary mixtures. In general, these results suggest that the flow and dynamic shear rheological properties of XG-GG binary mixtures are strongly influenced by a small addition of CMC.

Rheological characterizations of concentrated binary gum mixtures with xanthan gum and galactomannans

The steady and dynamic shear rheological properties of binary gum mixtures with xanthan gum (XG) and galactomannans (guar gum (GG) and locust bean gum (LBG)) were examined in a concentrated solution (1% w/w) as a function of gum mixing ratio (100/0, 75/25, 50/50, and 0/100). All samples, except for individual GG and LBG, showed high shear-thinning behavior with yield stress. The values of flow (K, ηa,50, and σoc) and dynamic rheological parameters (G′ and G″) of XG-GG and XG-LBG mixtures were significantly higher compared to XG alone, indicating that the flow and viscoelastic properties of binary gum mixtures were greatly affected by the addition of GG and LBG. The maximum elasticity synergistic interaction for XG-galactomannans mixtures was observed at a mixing ratio of 50/50, showing a greatly positive deviation between measured and calculated values of G′. These results suggest that the synergistic effect of GG and LBG addition on rheological properties of XG appears to be due to intermolecular interaction occurred between XG and galactomannans, as confirmed by dynamic rheological properties.

Steady Shear Rheological Properties of Native and Hydrothermally Modified Persian Acorn (Quercus brantii Lindle.) Starches

The steady shear rheological properties of native and hydrothermally modified Persian acorn starches at different concentrations (1, 2, and 3%) and temperatures (25, 40, 55, and 70 °C) were assessed. The rheological data of starch dispersions were fitted to the power law (R2 = 0.769–0.980) and Casson models (R2 = 0.904–0.994). According to the power law model, all native and hydrothermally modified starches presented shear‐thinning behavior with the flow behavior index between 0.697 and 0.933. The consistency coefficient (k) and apparent viscosity (ηa,100) of starches were in the range of 3.157–246.167 mPa sn and 2.212–74.443 mPa s, respectively. Based on the Casson model, the plastic viscosity (ηc) and yield stress (τ0c) of starches were in the range of 1.977–41.167 mPa s and 0.333–506.667 mPa, respectively. All rheological parameters, except for the flow behavior index, increased with increasing in concentration, and decreased with temperature. The temperature dependency of all the starches was well described by the Arrhenius model (R2 = 0.837–0.999). The activation energy (Ea) values were in the range of 4.47–12.96 kJ mol−1. The concentration dependency of all the starches in the temperature range of 25–70 °C was well fitted to the power law (R2 = 0.919–0.998) and exponential (R2 = 0.970–0.999) models. Generally, the rheological parameters such as k, ηa,100, ηc, and τ0c of native starch were maximum and those of annealing (ANN) starch were between those of native and heat‐moisture‐treatment (HMT) starches. These properties for dually modified starches were between those of single ones, showing that the second treatment could negate the effects of the first one.

Rheological and Pasting Properties of Naked Barley Flour as Modified by Guar, Xanthan, and Locust Bean Gums

To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased.