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Amylopectin with different side chain architecture and distribution were prepared by ɑ-amylase (AM) and maltogenic α-amylase (MA). The purpose of the study was to investigative the effect of molecular entanglement on the anti-thixotropy, gel properties, water distribution and viscosity properties. The results showed that MA specificity hydrolyzed chains ranging from DP 10–17 while retaining the long internal chains, while AM tended to trim the relatively longer chains of DP ≥ 12. The special (ŋ sp) in a double-logarithmic plot versus concentration exhibited two linear regions with changes of gradient at AM-M and MA-M polymer concentrations of about 6.20% and 1.31% (w/v), respectively. Higher storage modulus (G′) and final viscosity, and lower frequency dependence indicated the stronger gels of waxy maize starch were formed by MA modification, despite exhibiting a similar thixotropic loop area to AM samples. The microstructure of MA gels showed a more compact honeycomb-like network structure observed by SEM. These results confirmed the chain length profile of the amylopectin pruned by MA was more conducive to produce anti-thixotropic starch-based material. This study is beneficial to provide insights for customizing starch skeleton structure to meet specific industrial application requirements of starch-based products, especially where the rheological properties need to be precisely controlled. [Display omitted] • The entanglement concentration of amylopectin in MA-M was lower than that of AM-M. • MA-samples showed higher G′ and FV compared to AM-samples with similar thixotropy. • Microstructure of MA-samples was compact honeycomb-like network structure. [ABSTRACT FROM AUTHOR]

The creation of solid fat substitutes using food-grade biopolymers is currently an important focus of food researchers trying to develop healthier food products. In this study, emulsion-templated oleogels assembled from octenyl succinic anhydride starch (OS)-chitosan (CS) electrostatic complexes were prepared. The effects of the OS-CS complexes on the intermediate (emulsion) and final (oleogel) products were investigated. Emulsions stabilized by OS-CS complexes had greater interfacial layer stability and mechanical strength than those stabilized by only OS. The oil loss from the oleogels decreased significantly (p < 0.05) as the chitosan concentration was raised: from 10.28 to 1.5% oil loss for 0.1–1% CS. The rheological measurements showed that CS incorporation improved the viscoelasticity and thixotropy of the oleogels. In addition, adsorption of the OS-CS complexes inhibited lipid oxidation and hydrolysis due to its compact network and stable interfacial structure. Our results show that OS-CS complexes are effective emulsion-template oleogelators, which may be useful for creating new edible functional materials for application in the food industry. [Display omitted] • Octenyl succinic anhydride starch-chitosan complexes are an effective oleogelators. • Oleogels with tunable rheology can be obtained by adjusting chitosan content. • Chitosan significantly (p < 0.05) improved lipid oxidation of oleogels. • Chitosan effectively decreased the rate of lipid digestion of oleogels. [ABSTRACT FROM AUTHOR]

Jackfruit peel (JP) is considered as an agro-industrial lignocellulosic waste which can be utilized for cellulose isolation. In this work, a yield of 25.6% cellulose was obtained from JP powder through alkali (NaOH) and bleaching (NaClO 2) treatment along with the elimination of lignin, hemicellulose and other non-cellulosic constituents. The IR spectroscopy confirmed the existence of cellulose content in the final extracted product. The SEM images and EDX spectra demonstrated the microstructure of cellulose fibrils and their major elemental components as carbon and oxygen, respectively. The XRD data validated the crystalline (69.42%) nature of the cellulose. The various rheological attributes of cellulose suspension like the flow properties and dynamic rheological characteristics were examined at different pH, ionic strength and cellulose concentration. The cellulose suspensions exhibited shear thinning nature for all the pH, ionic concentration and cellulose concentrations. The change in viscoelastic behaviour of the cellulose suspension was noticed with the rise in storage modulus (G′) value with ionic concentration. The pH of the cellulose suspension had a significant impact on its viscoelastic properties due to the modifications in interfibrillar interactions of cellulose fibrils. The temperature ramp test showed that the G' is independent of the heating of cellulose suspension from 20 °C to 80 °C. The creep and thixotropic recovery test revealed that upon removal of stress, there is the recovery of strain and viscosity up to a certain extent, which is a characteristic property of viscoelastic material. [Display omitted] • Concentration, pH and salt addition had a significant effect on the rheology of cellulose. • Temperature ramp had less impact on viscoelastic properties of cellulose suspension. • Creep and thixotropy tests revealed the strain and viscosity recovery of cellulose. • SEM and EDX confirmed the microstructure and elemental composition of cellulose fibril. • Cellulose obtained from jackfruit peel has higher crystallinity. [ABSTRACT FROM AUTHOR]

During dysphagia management, the required foods are often thixotropic yield fluids (YSFs) in which polysaccharide gums are used as thickeners or gelling agents. Thixotropy is a prevalent hysteresis phenomenon in YSFs, so it always occurs as an apparently time-dependent stress or modulus response. The yielding behavior of the food bolus is inseparable from the mastication and swallowing process, among which time-dependent thixotropy is integral. Nevertheless, standardizing and generalizing the thixotropy levels has always been a challenge in the manufacturing application of YSFs. Moreover, the existing thixotropic approaches cannot guarantee the accuracy and comparability of the measurement process due to technicalities. Along these lines, in this work, the thixotropic stress-shear rate hysteresis loops were investigated based on the utilization of dysphagia management-oriented model polysaccharide solutions that exhibited different time-dependent thixotropy levels. More specifically, xanthan gum (XG), carboxymethylated curdlan (CMCD), and konjac glucomannan (KGM) solutions were selected to mimic dysphagia diet construction, whereas the relationship between their technically mechanical properties and structural changes was analyzed. Compared with the KGM solutions, both XG and CMCD solutions presented significant thixotropy levels with different timescale responses and concentration dependence. The recorded discrepancy in their loop area and shape were attributed to their different intermolecular association and networks. [Display omitted] • Thixotropy of dysphagia diet-oriented model polysaccharide solutions is studied. • Thixotropic stress-shear rate hysteresis loops are compared. • Timescale responses and concentration dependence of viscosity hysteresis are presented. • Modulus hysteresis behavior is described by multi-3iTT tests. • Relationship between macroscopic hysteresis and microscopic changes is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Blending with non-starch hydrocolloids is a crucial method to modify the processing properties of native starch. However, few comprehensive studies investigated the effects of inulin on the properties of rice starch (RS). In this research, we used three types of inulin with different degrees of polymerization (DP), namely, short-chain inulin (SI, DP < 10), middle-chain inulin (MI, DP > 10), and long-chain inulin (LI, DP > 23), to investigate the effects of inulin on the pasting, thermal, and rheological properties of RS and to provide the foundation for the application of inulin in RS-based food. Inulin addition increased the pasting temperature of RS and decreased all viscosity indices, including the peak, final, breakdown, and Setback viscosities of RS. Compared with LI, SI and MI exerted stronger influence on the viscosity indices of RS. The gelatinization temperature levels of the RS–inulin blends were higher than that of starch alone. The RS and RS–inulin blends exhibited a shear-thinning property, and stress–shear hysteresis loops were observed during shear. Thixotropy followed the order RS > RS-LI > RS-MI > RS-SI. Dynamic viscoelasticity results indicated that the RS and RS–inulin blends displayed weak gel-like behavior. Replacement of RS with LI and MI evidently increased the elastic properties more than the viscous properties of the RS–inulin blends. Graphical abstract Image 1097 Highlights • Inulin increased the pasting temperature of RS and decreased viscosity indices. • The RS and RS–inulin blends exhibited a shear-thinning property. • The addition of inulin improved the shear stability of RS. • The thixotropy of RS decreased by inulin addition. [ABSTRACT FROM AUTHOR]

The sol-gel performance of wheat starch (WS) is of great importance for the processing and quality management of flour-based products. Herein, how acetylated starch (AS) inclusion modulates those properties of wheat starch-based system was understood using different techniques, e.g., rheological analysis and X-ray diffraction (XRD). Compared with WS alone, the resultant WS-AS binary system exhibited lower setback viscosity (corresponding to inhibited starch retrogradation as verified by XRD), zero-shear viscosity, moduli, and gel strength, accompanied by a suppressed sol-gel transition. Also, from thixotropy tests, the binary system with AS (WS-8%AS) presented the weakest thixotropy in hysteresis loop and a greater in-shear recovery property (as indicated by the three interval thixotropy test (3-ITT)), and the systems containing 6%–8% AS were proved to show good sol-gel properties. The property improvement could be related to the inhibited retrogradation, according to correlation analysis. In addition, the gel freeze-thaw stability of WS-AS systems was reduced as compared to WS, probably related to phase separations. The present information would facilitate the design of wheat starch-based matrices with regulated quality attributes. [Display omitted] • Incorporating acetylated starch reduced modulus, viscosity and thixotropy of binary sol. • Incorporating acetylated starch lowered hardness, chewiness and strength of binary gel. • Incorporating acetylated starch delayed the sol-gel transition of binary system. • Phase separations probably occurred in the wheat starch-acetylated starch binary system. • Including 6%–8% acetylated starch improved the performance of wheat starch-based system. [ABSTRACT FROM AUTHOR]

Prosopis ruscifolia (or vinal tree) is an abundant plant from Argentina semiarid areas, whose seeds contain a galactomannan type interesting gum: vinal gum. The aim of this work was to analyze the rheological behavior of vinal gum suspensions and the consequences of its interactions with commercial gums widely employed in the food industry. V inal gum aqueous suspensions were in good agreement with the Cox-Merz rule at concentrations lower or equal to 1% (w/w), which establishes an empirical relationship between complex and apparent viscosity. The flow curves of vinal gum could be defined only by two parameters -Newtonian viscosity (η 0 ) and strain rate ( γ ˙ 0.1 )- and the shear-thinning behavior of vinal gum complied with the generalized curve for other polysaccharides. In mixtures with xanthan gum, vinal gum exhibited a synergistic relationship on its elastic behavior (at a total gum concentration of 1% (w/w)). On the other hand, vinal gum showed no synergism with κ- carrageenan or sodium alginate at the same total concentration of polymer. Apparent viscosity of v inal gum aqueous suspensions showed Arrhenius type dependence with temperature, as other galactomannans. The rheological behavior was not dependent on shear time, and the thickening power of vinal gum was slightly affected by pH and ionic strength changes. The present work provides detailed information on rheological characteristics of a non-traditional galactomannan extracted from an abundant and available source, being a starting point for possible applications of vinal gum as thickening and/or stabilizing agent in food, pharmaceutical, paper, textile, oil and cosmetics industries. [ABSTRACT FROM AUTHOR]

In this paper, a first robust scheme for in-depth rheological study on the interaction of two attractive hydrocolloids (sage seed gum (SSG) and xanthan gum (XG) at five blending levels (1-0, 3-1, 1-1, 1-3, and 0-1)) was defined by utilizing flow behavior, thixotropy and viscoelasticity measurements. Shear thinning as the important rheological behavior of biopolymers were found to be broadly different in steady and dynamic shear tests. We attributed this difference to the longer timescale of segment-segment interaction in SSG chains than that of XG. A well-developed three-parametric exponential model satisfactory fitted the recovery phase data of in-shear structural recovery test. There was a negative correlation between time effects in SAOS (small amplitude oscillatory shear) and thixotropy with R 2 equal to −0.90. The highest recovery parameter (83.25%) and the lowest extent of time dependency (determined in SAOS) were obtained for XG. Excellent correlation existed between the extent of time dependency and the difference between static and dynamic yield stresses ( R 2 = 94–96%). The highest and lowest departure values from Cox - Merz rule were found for SSG (83.87%) and XG (46.18%), respectively. The strongest interaction between SSG and XG among all ratios tested, occurred for 3-1, which was confirmed by the Cole - Cole plot. [ABSTRACT FROM AUTHOR]

A comparative study of both the bulk and air/liquid interfacial rheological responses was carried out by using four kinds of representative high molecular weight and highly branched polysaccharide emulsifiers, (a) corn fiber gum (CFG), (b) octenyl succinate anhydride-modified starch (OSA-s), (c) gum arabic (GA) and (d) soybean soluble polysaccharides (SSPS), spanning the concentration range of 1–15 wt%. We found that the bulk and interfacial rheological properties of their aqueous solutions were significantly different. While both CFG and OSA-s showed Newtonian flow behavior at higher concentrations, both GA and SSPS exhibited obviously shear thinning behavior or thixotropy even at a low concentration of 1 wt%. The time-dependent flow behavior for CFG, GA and SSPS reflected microstructural breakdown and rebuilding in solutions under shear, indicated that their proteinaceous portion was strongly bound to their polysaccharide part. This phenomenon was not observed for the almost protein-free OSA-s. The interfacial rheology responses showed that the layers formed by CFG and OSA-s were viscously predominant with faster formation kinetics while they were elastically predominant for GA and SSPS with slower formation kinetics. Interfacial viscoelastic responses of CFG and OSA-s were weaker than those of GA and SSPS. By comparison, the interfacial layer for OSA-s showed pure viscous responses whereas SSPS showed the highest elastic responses. These significant disparities in bulk and interfacial viscoelasticity of the four polysaccharide emulsifiers reflect the influence of different fine chain structures on the dissimilarity in the intermolecular associations and the architectures of the interfacial layers. [ABSTRACT FROM AUTHOR]

In this study, rheological properties of cress seed gum (CSG) and its fractions (F1, F2, F3; fractionated using stepwise extraction with water) were investigated. Cress seed gum and its fractions revealed random coil conformation in dilute regimes; chain flexibility and intrinsic viscosity increased from F1 to F2 to F3. The mechanical spectra derived from strain sweep and frequency sweep measurements indicated that the gum dispersions had viscoelastic behavior; all of them were classified as weak gels and the gel network got stronger along the series of F1, F2 and F3. Arrhenius-type model was used to describe the effect of temperature; F2 and F1 showed the highest and the lowest activation energy, respectively. All gum dispersions displayed thixotropic behavior; hysteresis loop area and structural recovery increased significantly along the series of F1, F2 and F3. In general, the results indicated that CSG and the fractions exhibited significantly different rheological properties. [ABSTRACT FROM AUTHOR]

Conjugation of plant proteins with phenolic compounds has been an efficient strategy to improve the limited capacity of this kind of protein to stabilize emulsions. In this sense, the stabilizing capacity of lupin protein-grape seed extract conjugates in the form of nano (NC) or micro (MC) particles was evaluated in oil-in-water emulsions. Covalent binding between lupin protein isolate (LPI) and grape seed extract (GSE) was confirmed by quantification of total free sulfhydryl groups and fluorescence assays in both NC and MC for all GSE concentrations tested (0.04–0.12 wt%). The main differences between MC and NC were the larger size and surface hydrophobicity of the former, reflecting different stabilizing capacities. The droplet size and microstructure of all emulsions after 28 days of storage suggest that NC- and MC-stabilized emulsions were highly stable to coalescence. However, NC produced emulsions with a higher tendency to flocculation. Increasing the GSE concentration in the conjugates attenuated the droplet flocculation, resulting in emulsions with improved kinetic stability. Results indicate that the dominant stabilizing mechanism of the conjugates is Pickering-type, although others may occur simultaneously. Indeed, MC produced emulsions with better stability with no visible creaming and more complex rheological properties. A gel-like behavior (G'>G") was observed from oscillatory rheology, which was considered an additional stabilizing mechanism. In contrast, NC produced emulsions with predominantly liquid-like behavior (G">G'). Shear resistance was evaluated after homogenization of the emulsions, showing that the 3D network formed in the emulsions was rapidly recovered, including the highly structured MC-stabilized emulsions. Different properties of emulsions stabilized by NC or MC indicate potential varied applications in the food industry. The conjugation of GSE with LPI showed improvements in the overall stability of the emulsions, demonstrating the great potential for usage of these conjugates in the formulation of highly stable emulsion-based systems, even using a protein of limited stabilizing capacity. [Display omitted] • Conjugation of GSE with LPI modulated the hydrophilic/hydrophobic character balance of the protein. • MC-stabilized emulsions presented higher stability than NC-stabilized emulsions. • Pickering coupled with other stabilizing mechanisms resulted in emulsions with high resistance to coalescence. • MC-stabilized emulsions showed a 3D network and superior viscoelastic properties over time. [ABSTRACT FROM AUTHOR]

This work appears to be the first example with respect to two points: First, a film from salep, a glucomannan based hydrocolloid was formed and characterized in terms of interfacial properties. Second, three interval thixotropy test (3ITT) was applied to determine effect of instant interfacial shear stress or shear rate on deformation and regeneration of salep glucomannan (SG) films at air/water interface. In order to assess the interfacial properties, the salep from which SG films was formed was also characterized in terms of compositional, molecular, thermal and surface properties. To determine interfacial properties, the SG films prepared at different concentrations (2–3%) were formed at the water/air interface. Amplitude and frequency sweeps were applied to characterize the structure of the films at equilibrium, revealing a gel-like structure of the SG films at equilibrium. 3ITT revealed that shear rate/stress levels at different concentrations resulted in a remarkable deformation in SG films whereas they were fully recoverable, showing regeneration after distortion by a steady shear flow, as demonstrated by decreasing deformation percentage ( D r ) values and increasing time required for the recovery ( R time ) values at increasing concentrations. 3ITT appeared to be an effective tool to simulate and analyze effects of real pumping, mixing and instant stirring processes during production and handling steps of SG films. The SG films were proven to have improved interfacial properties, which suggests that they may be an alternative to other hydrocolloid based films in terms of adsorbing onto air-water interfaces to reduce surface and interfacial tensions. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different purification methods (ethanol (sample E), isopropanol (sample I) and ethanol-isopropanol (sample EI)) on intrinsic viscosity, steady and dynamic rheological properties of cress seed gum were investigated. The gum dispersions exhibited viscoelastic properties, the storage modulus (G′) was higher than the loss modulus (G″), and mechanical spectra of the crude and purified cress seed gums were classified as weak gels. The purified samples had stronger and more elastic network structure than the crude gum (CSG) and the gel network got stronger along the series of I, EI and E. All the gum dispersions indicated shear-thinning behavior and the viscosity of the samples followed the order of E > EI > I > CSG. Herschel-Bulkley model was the best model to describe steady shear flow behavior and Arrhenius-type model was also applied to describe the effect of temperature. Crude cress seed gum and EI showed the highest and the lowest activation energy, respectively. The crude and purified gums indicated thixotropic behavior and CSG exhibited the lowest hysteresis loop area and the highest structural recovery. All the samples revealed random coil conformation in dilute regimes, and chain flexibility and intrinsic viscosity enhanced after purification. Intrinsic viscosity of the purified samples increased along the series of I, EI and E. [ABSTRACT FROM AUTHOR]

Partial denaturation of whey protein concentrates has been used to make protein powders with differing viscosity properties. PDWPC particles have been manufactured to have a range of aggregate sizes (3.3–17 μm) and structures (compact particle gel to open fibrillar gel). In solution the PDWPC samples show complex viscosity behaviour dependant on the size and morphology of the PDWPC aggregate particles. For the same protein content the compact particles have a lower viscosity than open, fibrillar particles. The viscosity also appears to depend on the surface structure of the particles, with particles of a similar size, but having a rougher surface giving higher viscosity than similar smooth particles. The viscosity of the WPC, MPWPC and PDWPC solutions are explained in terms of the postulated interactions between the protein aggregates in solution. [ABSTRACT FROM AUTHOR]

In the present paper, the functionality of basil seed gum (BSG), guar gum (GG) & their blend (MGB, 50:50), at the concentration of 0.35, 0.45, 0.50 and 0.55%, related to the rheological, physical and sensory characteristics of low fat ice cream (2.5% fat) was compared with full fat sample (10%) as control. Shear thinning and thixotropic behaviors of all mixes were well described by Herschel–Bulkley and second-order structural kinetic models, respectively. The results showed that BSG and MGB, by producing high consistency coefficient ( k ), yield stress ( τ 0 ), thixotropy rate constant ( k ), extent of thixotropy ( η 0 /η ∞ ) and low flow behavior index (n) values, provided satisfactory rheological properties in low fat ice cream. Fat reduction resulted in some defects which to some extent compensated by increasing levels of fat replacers. BSG & MGB exhibited a more shear-sensitive thixotropic nature than GG mixes and strongly favored perception of creaminess which was more than full fat mixes in some concentrations. In addition, they depressed the coldness and coarseness perception of low fat mixes. Addition of BSG reduced the meltdown rate and extent of melting at all concentration compared to the GG and MGB mixes, which two latter gum systems showed almost equal value of these properties. Furthermore, significant correlation between the values of melting rate data and rate of breakdown parameters of the mixes was observed. The results presented herein showed that BSG and its blend with GG are very suitable fat replacers/stabilizers for low fat ice cream. [ABSTRACT FROM AUTHOR]

Antarctic krill ( Euphausia superba ) offers a high potential for development of innovative food products due to its large reserves and satisfied nutritional values. This study aimed to evaluate the thickening function of heat-induced krill protein fluid gels through the investigation of their flow behavior and microstructure. The microstructure of these physical gels was classified as four types, including particulate gels (pH 5.5), transition state from particulate to branched gels (pH 6.0), loose connected networks (pH 6.8, 7.0, 8.0 and 8.6) and fine cross-linked structure (pH 6.4, 7.2 and 7.5). Gels at pH 5.5 and 7.2 showed significantly higher gel strength in comparison with their counterparts at other pHs. Fluid gels showed characteristic non-Newtonian pseudoplastic behavior with low flow behavior indexes in the shear thinning region. Fluid gels at pH 7.2 showed significantly higher viscosity in comparison with other gels, which was related with its viscoelasticity and microstructure. Fluid gels with branched networks exhibited significantly better water binding capacities than particulate gels. Fluid gels became less pseudoplastic as temperature increased, which resulted from the melting of gels. The thixotropy of fluid gels was demonstrated through loop test, stepwise test and start-up flow experiment. Particulate gels at pH 5.5 showed smaller thixotropy in comparison with branched gels at higher pHs. Fine connected fluid gels showed lower structural recovery than loose cross-linked gels under stepwise test. This resulted from the irreversible damage of fine connected structure under high shear rate. Heat-induced fluid gels of krill protein exhibited thickening function and could be applied in food development with desired requirement. [ABSTRACT FROM AUTHOR]

Extruded and native wheat flours were combined with agars ( Gracilaria and Gelidium ) and carrageenans (κ-carrageenan and ι-carrageenan) to modify their paste and gel properties. Combinations of extruded flours with hydrocolloids produced an increase in the hydration properties (swelling volume and water holding and water binding capacities). All hydrocolloids (particularly ι-carrageenan) also produced an increase in hydration properties after combination with native flours. With regard to the pasting properties of native flours combinations, all hydrocolloids produced an increase in peak viscosity (particularly Gelidium agar), but only agars decreased the onset temperature of gelatinization and increased breakdown, indicating a different mechanism of action. In the presence of extruded flour, the incorporation of hydrocolloids increased the cold viscosity of flours in very different ways depending on the hydrocolloid. Both native and extruded flours exhibited higher G′ and G″ values and a lower tan δ after the incorporation of carrageenans, which, together with the lower dependence on frequency, would produce stiffer and more stable pastes/gels. Based on gel properties, greatest hardness with native and extruded flours was achieved by the incorporation of carrageenans. In general, carrageenans, besides producing stiffer and more stable pastes, gave rise to harder and clearer gels compared to those made with agar, for both their combination with extruded and native wheat flours. Meanwhile, pastes made with combinations of extruded flours and agar showed higher thixotropy. [ABSTRACT FROM AUTHOR]

Abstract: Beyond their nutritional importance, starches present a relevant technological role in processed foods. The gelatinization process that occurs during heating of starch suspensions is generally followed by considerable shearing rates, which affects the rheological behavior. This work investigated the rheology of gels produced from Peruvian carrot (Arracacia xanthorrhiza B.) starch at different concentrations (2, 6, and 10%) and temperatures (10, 30, 50 and 70 °C), using rheological measurements under steady and oscillatory shear. In addition, the system microstructure was analyzed by optical microscopy around the gelatinization temperature (59.5–61 °C). The gels exhibited shear thinning behavior and high thixotropy. Power Law was fitted to flow curves and the consistency index was affected by temperature and starch concentration. Steady and oscillatory shear measurements showed that the rheological behavior was highly dependent on the fraction of gelatinized starch granules, which in turn was affected by water availability and temperature. Depending on temperature and concentration, Peruvian carrot starch resulted in more viscous or more elastic systems, which could be applied in different gel-like foods. Its low gelatinization temperature contributes to easy cooking and high digestibility, but technological applications must take into account its high susceptibility to intense shearing. [Copyright &y& Elsevier]

Abstract: Understanding of the rheological behavior of sodium alginate (SA) is fundamental either to design optimized products or to ensure stable flows. Of the SA samples tested that characterized by a M/G ratio of 0.38 and a weight–average molecular mass (Mw) of 1.180 × 105 g/mol, steady–shear flow, thixotropy and dynamical viscoelasticity tests were carried out to characterize rheological behavior of G–rich SA aqueous solutions as influenced by concentration (1.0–3.0%, w/v) and temperature (5–35 °C). These measurements were carried out by using an Anton Paar–Physica MCR 301 Rheometer. It was found that, above a critical shear rate, all G–rich SA solutions (1.0–3.0%, w/v) exhibited non–Newtonian shear–thinning behavior and the flow curves could be well described by the Cross model. The temperature–dependent behavior of 2.5% (w/v) SA had higher correlation to the Cross model and the Arrhenius relationship, while the flow activation energy tended to decrease with the increase of shear rate. The upward–downward rheograms showed that all the systems evaluated in this paper had a hysteresis loop which indicating strong thixotropic behavior, the higher the SA concentration, the stronger the thixotropic behavior. The dynamical viscoelastic properties characterized by oscillatory frequency sweep under small–deformation conditions showed a fluid–like viscoelastic behavior. The behavior of SA aqueous solutions was predominantly more viscous than elastic. Multiwave temperature ramp test for 2.5% SA aqueous solutions was consistent with the results from oscillatory frequency sweep test. [Copyright &y& Elsevier]

Abstract: The effects of pH and electrolytes (NaCl and CaCl2) on the viscosity, dynamic modulus (storage modulus G′ and loss modulus G″) and thixotropy of aqueous solution of new exopolysaccharide (SM-A87 EPS) secreted by a deep-sea mesophilic bacterium Wangia profunda SM-A87 were investigated. It was found that at pH 3–12 and the electrolyte concentration of 0.1–80 g/L, the SM-A87 EPS solution showed very weakly pH-dependent and salt-dependent rheological properties and dominant elastic behavior. These properties were considered to arise from the hyper-branched structure of the SM-A87 EPS molecules through the comparison of rheological properties of SM-A87 EPS solutions with those of partially hydrolyzed polyacrylamide ones at different electrolyte concentrations. Such good pH stability and salt resistance of the SM-A87 EPS solution indicate that SM-A87 EPS has great potential for application as food additive, thickener, stabilizer and enhanced oil recovery system. In the studied conditions, 2 g/L SM-A87 EPS solution showed positive thixotropy. The relative thixotropic recovery decreased with pH increasing and the electrolyte concentration decreasing. [Copyright &y& Elsevier]

Abstract: The present paper proposes an objective classification of commercial thickened food widely used in patients with dysphagia. A total of 34 commercial enteral nutrition products were analyzed (beverages, main courses and desserts) corresponding to 6 different commercial brands. All these products contain different hydrocolloids (i.e., starch, xanthan gum, carrageenans, etc.) as thickeners, in order to get the desired texture. Joint consideration has been made of viscous behavior (flow and thixotropy) and viscoelastic behavior (oscillatory testing). Rheological measurements were fitted to different rheological and empirical mathematical models, and a total of 11 parameters were generated. Based on these parameters and the use of fuzzy clustering and the c-means method, an objective classification of all the products was obtained. Our results correspond to five different classes, one more than the four established by other authors. The five defined classes have been named in a way similar to those most commonly used in the literature. Each class has been defined from the parameters of the centroids generated by the classification method used – thus allowing us to know the common rheological characteristics of any of the products belonging to a given class. [Copyright &y& Elsevier]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: The influence of molecular association on the rheological behavior of gum arabic solution was studied. Using time-dependence of transient shear stress a reversible molecular association could be arrested and the thixotropy of gum arabic solution was interpreted. The structural breakdown, buildup and the effect of shear history due to molecular association could be related using the Casson’s equation. Stress jump measurements distinguished the effect of molecular association on the elastic and viscous contributions of shear stress. An elastic-like contribution dominated at low shear rates whereas the viscous component became important at high shear rates. The elastic contribution was strongly affected by the molecular association of gum arabic, with increased molecular association contributing to a larger elastic contribution. The elastic and viscous contributions were also investigated in transient flow. Both of the contributions increased with rest time, indicating a buildup of molecular association. With increasing the rest time the elastic contribution increased much faster than the viscous contribution to the total stress. [ABSTRACT FROM AUTHOR]

Abstract: 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 (Ea ) 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. [Copyright &y& Elsevier]

Abstract: The characterization of maturing gelatin solutions in shear flow is required for an appropriate formulation of food products. Under static conditions, the maturation process of gelatin solutions may be described through a basic structural parameter evolving to the percolation value (gel point). Within the rheological framework, two asymptotic viscosities are well identified for the maturing process of gelatin solutions at the limit zero shear rate. One involves the initial solution viscosity that may be associated with the null structural parameter (the microstructure is not formed yet). The other is the percolation zero shear rate viscosity (assuming an infinite value when approaching the gel time) and corresponds to the maximum value of the structural parameter. Under flow, thixotropic theories combined with the knowledge of suspension rheology allow one to convert directly experimental data obtained as shear stress versus time for a given shear rate into the time evolution of the structural parameter. Consequently rheometric experimental data available places the search for a rheokinetic model of the structural parameter. Here, different expressions for this model are investigated, mainly those involving both the rates of structure breakdown and buildup, where the average cluster size is affected by the shear rate. The rate equation thus obtained may be then applied to arbitrary shear rate histories. Numerical results of the rheokinetic model proposed in this work fit well experimental rheometric data obtained in shear flow for the maturing of different gelatin solutions. Experimental data acquired in this work are presented and discussed in relation to those reported previously in the literature. [Copyright &y& Elsevier]

ABSTRACT: The flow curves and time-dependent rheological behavior of two traditional Iranian hydrocolloids obtained from Salep tubers (wild terrestrial orchids) and Balangu seeds (Lallemantia royleana) have been investigated. All samples exhibited thixotropic behavior at the concentrations used and both in forward and backward measurements were characterized by the power law model. At the constant shear rate, the apparent viscosity decreased rapidly with time of shearing within the first 100s for Salep and 50s for Balangu samples, and approached a constant value corresponding to a steady state after approximately 450 and 250s, respectively. The breakdown rate of all samples accelerated at higher shear rates. Four time-dependent models namely the second order structural kinetic model, Weltman model, first-order stress decay models with zero and non-zero equilibrium stress values were used to describe the thixotropy behavior and different parameters of these models were analyzed. The results showed that the rate of the thixotropic breakdown increased with increasing shear rates for Salep, whereas, the extent of thixotropy increased with shear rate for Salep and decreased for Balangu. In this study, the selected hydrocolloids were adequately modeled by the first-order stress decay model with non-zero equilibrium stress value. [Copyright &y& Elsevier]

Abstract: The thixotropic behavior of locust bean gum (LBG) in sucrose solutions after freezing and thawing was investigated using a transient rheological approach. The thixotropy is attributed to the forced association of LBG chains during freezing. The effects of shear rate, shearing temperature, sucrose concentration, and number of freeze–thaw cycles on the transient viscosity profile were studied. A second-order kinetic equation for structure breakdown is found to describe well the transient viscosity profile, showing a rate constant of an order of 0.1s−1 in terms of the dimensionless structure parameter for the 2.5% LBG 30% sucrose solution. The rate constant strongly depends on the shear rate, shearing temperature, and number of freeze–thaw cycles, the last dependence indicating its relation to the pore size of LBG network. The ratio of the initial to equilibrium viscosity η 0/η ∞, reflecting the amount of associations ruptured under shear, appears almost constant throughout the measurement. It is speculated that only part of the associations can be probed at a constant shear rate. For the LBG solutions with sucrose content below 15% or subjected to successive freeze–thaw cycles, transient viscosity profiles cannot be obtained due to elasticity caused by the formation of an infinite polymer network. [Copyright &y& Elsevier]