Rheological Properties Of Gels Research Articles

Effect of different polyols on wheat and maize starches paste and gel properties

The use of polyols as sugar replacers in bakery products is a common practice. In these products, pasting and gelation properties of starches have a strong influence on the process and on the quality of final products. In this study, the influence of different polyols (maltitol, sorbitol, xylitol and mannitol) on pasting properties of two starches (wheat and maize) was analysed and compared to those made only from native starches and their combinations with sucrose. Rheological properties of gels as well as their texture and colour were also analysed. Even though differences among the different studied polyols and the interactions among them and among starches were observed, in general polyols showed an influence on starch properties similar to those of sucrose. Thereby, in general peak viscosity and setback as well as gel hardness were increased and L* was reduced with the use of polyols. In all cases, the polyol which showed more similar results to those made from sucrose was maltitol. Meanwhile, xylitol was the polyol which modified the native starch properties to a lesser extent, both in RVA curve, especially in the cooling stage, and in gel rheology and hardness.

Effect of Okara on Textural, Color and Rheological Properties of Pork Meat Gels

AbstractThe objective of this study was to investigate effect of okara on the textural, color and rheological properties of pork meat gels. Pork meat gels with okara had better cooking characteristics than those without okara. As okara content increased in pork meat gels, there were significant increases in lightness (L*), hardness, chewiness and breaking force of gels but decreases in cohesiveness, while there was no significant difference found in gel springiness and resilience. Addition of okara also increased storage modulus (G′) and loss modulus (G″) of pork batters during the heating. Loss tangent (tan δ) patterns indicated that okara facilitate to hold more water and accelerated the denaturation to form an elastic gel network. Overall, okara can be used as an ingredient to improve the quality of pork‐based products, especially to replace animal fats.Practical ApplicationsResults of this investigation could have a potential for developing a novel meat product that contains dietary fiber since a product with better functionality, lower cost and more nutritional benefit is very importance for the meat processing industry.

Effect of Extraction Time on the Rheological Properties of Sericin Solutions and Gels

Recently, silk sericin has attracted the attention of researchers owing to its useful properties as a biomaterial including 1) good wound healing and cell activities, 2) fast gelation character, and 3) high water retention property. In the present study, silk sericin was prepared using different extraction times in hot water and the effect of extraction time on the rheological properties of sericin solutions and gels was examined. It was found that the production yield of sericin increased with extraction time. The shear viscosity of sericin solutions and gels decreased with increasing extraction time due to a decrease in sericin molecular weight. When the sericin solution transformed to a gel, the viscosity increased and the shear thinning behavior was more evident. In addition, the shear stress measurements indicated that the slip between the sericin samples and the measuring plate of the rheometer was increased by the gelation of sericin. The compression strength of sericin gel could be increased remarkably (by more than 100 fold) by preparation using the freezing and thawing method.

Characterization of water extractable arabinoxylans from a spring wheat flour: rheological properties and microstructure.

In the present study water extractable arabinoxylans (WEAX) from a Mexican spring wheat flour (cv. Tacupeto F2001) were isolated, characterized and gelled and the gel rheological properties and microstructure were investigated. These WEAX presented an arabinose to xylose ratio of 0.66, a ferulic acid and diferulic acid content of 0.526 and 0.036 µg/mg WEAX, respectively and a Fourier Transform Infra-Red (FT-IR) spectrum typical of arabinoxylans. The intrinsic viscosity and viscosimetric molecular weight values for WEAX were 3.5 dL/g and 504 kDa, respectively. WEAX solution at 2% (w/v) formed gels induced by a laccase as cross-linking agent. Cured WEAX gels registered storage (G’) and loss (G’’) modulus values of 31 and 5 Pa, respectively and a diferulic acid content of 0.12 µg/mg WEAX, only traces of triferulic acid were detected. Scanning electron microscopy analysis of the lyophilized WEAX gels showed that this material resembles that of an imperfect honeycomb.

Effect of sucrose, stevia and xylitol on rheological properties of gels from blends of chestnut and rice flours

The development of high quality gluten-free products requires the understanding of the phenomena that dictate the ingredient interactions commonly used in foodstuff. In this work, the main objective was to develop alternative gluten-free gelled desserts from blends of chestnut flour (Cf) and whole (Rw), Agulha (Ra) or Carolino (Rc) rice flours. The impact of sucrose, stevia and xylitol on textural, rheological and structural properties of selected gels was investigated. Texture results indicated that studied gels in the presence of sucrose and xylitol decreased significantly the firmness. Rheological outcomes showed that the temperature ramps on heating of Cf/Rw gels were similar to those obtained for Cf/Ra, whereas Cf/Rc gels presented a particular pattern. The presence of sucrose resulted in a significant decrease in the values of storage and loss moduli. Confocal microscopic images showed that the sugar addition leads to a less aggregated structure with fracture lines well marked.

Rapid Heating of Alaska Pollock and Chicken Breast Myofibrillar Proteins as Affecting Gel Rheological Properties

Surimi seafoods (fish/poikilotherm protein) in the U.S.A. are typically cooked rapidly to 90+°C, while comminuted products made from land animals (meat/homeotherm protein) are purposely cooked much more slowly, and to lower endpoint temperatures (near 70 °C). We studied heating rate (0.5, 25, or 90 °C/min) and endpoint temperature (45 to 90 °C) effects on rheological properties (fracture, small strain) of washed myofibril gels derived from fish (Alaska pollock) compared with chicken breast at a common pH (6.75). This was contrasted with published data on gelation kinetics of chicken myosin over the same temperature range. Heating rate had no effect on fracture properties of fish gels but slow heating did yield somewhat stronger, but not more deformable, chicken gels. Maximum gel strength by rapid heating could be achieved within 5 min holding after less than 1 min heating time. Dynamic testing by small strain revealed poor correspondence of the present data to that published for gelling response of chicken breast myosin in the same temperature range. The common practice of reporting small-strain rheological parameters measured at the endpoint temperature was also shown to be misleading, since upon cooling, there was much less difference in rigidity between rapidly and slowly heated gels for either species.

Interconvertible Self‐Assembly and Rheological Properties of Planar Bilayers and Vesicle Gels in Anionic/Nonionic (CF/CH) Surfactant Solutions

The surface and bulk properties of aqueous mixtures of nonionic tetraethylene glycol monododecyl ether (C12EO4) and anionic perfluorolauric acid (PFLA) were studied. These mixtures exhibited pronounced synergistic effects in terms of their mixed micellization and rheological properties. Only one type of mixed micelle is formed in dilute mixed solutions. At low PFLA content, with increasing the total surfactant concentration, short thread-like micelles grow to form larger discs. On increasing the amount of PFLA, owing to the fact that the fluctuant planar bilayers of nonionic C12EO4 become charged, vesicle gels that are comprised of densely packed unilamellar and multilamellar vesicles spontaneously form, in which the fluorocarbon chains in the bilayers are in a fluid state at room temperature. The elastic properties and the yield stress of the lamellar solutions largely increase upon the addition of small amounts of PFLA and they then pass through a maximum at a saturation of effective membrane charge density. Interestingly, increasing the pH value of the gels causes a backward transition from stiff vesicles to flexible planar bilayers. On increasing the amount of NaOH, the bilayers exhibit greater flexibility, owing to the decrease in membrane charges, along with a large decrease in the solution viscosity and their elastic properties. The combination of strong stability of the vesicle gels with the interconvertible transition of bilayers and vesicles is expected to be of practical use for controlled drug delivery and release.

Kappa carrageenan fluid gel material properties. Part 1: Rheology

With the potential use of kappa carrageenan (κC) fluid gels in reduced fat foods, an understanding of their rheological properties was explored. Isotropic fluid gel particles were produced via sheared gelation of κC with potassium chloride. Bulk fluid gel rheological properties were tested for their dependence on particle elasticity and volume fraction (controlled through biopolymer concentration and dilution, respectively). To achieve this, a method for determining fluid gel particle volume fractions (ΦFG) was devised using a novel centrifugation technique whereby the dependence of particle compressibility on centrifugation force is accounted for. The κC fluid gels prepared here are suggested to behave as soft microgel particles with penetrable hairy chains allowing for particle overlap, and aggregation at low volume fractions. The ‘hairy’ structures are proposed to arise from incomplete helix formation during gelation (which we previously confirmed using calorimetry) as a result of the applied shear disrupting the molecular ordering process which, for κC, is slow relative to that of biopolymers that do not form ‘hairy’ fluid gel structures.

Effect of Maltodextrins on the Rheological Properties of Potato Starch Pastes and Gels.

The study examines the effects of maltodextrins saccharified to various degrees on some rheological properties of potato starch dispersions. Pasting characteristics, flow curves, and mechanical spectra were determined for native potato starch and for its blends with potato maltodextrins having dextrose equivalents (DE) of 10.5, 18.4, and 26.5. The results showed that medium-saccharified maltodextrin (DE = 18.4) gave the strongest effect, manifesting itself as a considerable reduction in the viscosity at pasting, a decrease in apparent viscosity during flow, and a decrease in the storage and loss moduli. Addition of high-(DE = 26.5) or low-(DE = 10.5) saccharified maltodextrins had a markedly smaller effect on the rheological properties of starch. The differences in the effects produced by the maltodextrins are closely connected to the degree of polymerisation of the maltooligosaccharides in the systems.

Rheological Characteristics of Sour Cherries in Gels Containing Waxy Maize and Cassava Starches

AbstractEight gels composed of sour cherries, starch ingredient, sucrose, potassium sorbate and citric acid were prepared using the same recipe. The starch component was waxy maize (WM) or cassava (CA) starch or their blends with cold water swelling (CWS) starches. The gels varied only in the origin and type of chemical modification of starch (acetylated distarch adipate, hydroxypropylated distarch phosphate). Rheological properties of the gels were studied. Flow tests showed that all samples were pseudoplastic and exhibited shear thinning behavior with tendency to yield stress. The structural recovery of the cherry gels was above 55% and was clearly dominated by the origin of the starch. Linear viscoelastic data showed that all fruit gels exhibited weak gel‐like structure. Classification of gels into two different types was confirmed both in results of steady flow and low amplitude oscillatory tests. Cherry gels containing modified WM starches showed very good heat and rheological stability, whereas gels based on CA starches and their blends with CWS WM starches were more susceptible to shear rates and increased temperature.Practical ApplicationsFruit gels are popular low‐level sugar products used mainly in confectionery. It is very important to provide appropriate viscosity of this product (thick or thin, depending on its usage). Starch is commonly used in production of modern food, mainly to modify its texture and to improve food stability during storage. This research was developed to study the effect of starch addition on the rheological properties of cherry gels. Published works provide information for researchers on this area of study and enable producers to make fruit gels of great consumer's acceptability.

Impact of High Hydrostatic Pressure and Heat Treatments on Milk Gel Properties: A Comparative Rheological Study

The effects of high hydrostatic pressure (483 and 676 MPa at 20°C for 5 min) and heat treatment (63°C for 30 min and 72°C for 15 s) of milk on the rheological properties of coagulant-induced milk gels were investigated. The rheological properties of gels were determined using a dynamic Physica Rheometer and Texture Analyzer. Milk turbidity was measured by a spectrophotometer. The gels produced from a pressure of 483 MPa had higher storage modulus (G*) and firmer gel at cutting compared to heated milks. Increasing the pressure to 676 MPa caused a reduction in G*, less firm gels, and an increase in milk turbidity compared to 483 MPa and heated milks. The differences between the gels formed from different pressure- and heat-treated milks, suggesting that the structure network of gels were considerably altered by high hydrostatic pressure treatment of milk. Disruption of casein micelles and denaturation of whey proteins caused by high hydrostatic pressure treatments were responsible for most of the effects observed in this study. In general, pressurizing the milk at 483 MPa at 20°C was a promising treatment for the manufacture of coagulant-induced milk gels with good rheological properties; however, pressurization at 676 MPa could not be recommended.

Influence of sterilization on the rheological properties of different types polyacrylic acid gels

The aim of the study was to analyze the influence of sterilization conditions on the rheological properties of gels containing polyacrylic acid derivatives (Carbopols: 974P, Ultrez 10 and Ultrez 20). The gels utilized in this study contained 0.5% (w/w) metronidazole, antiprotozoal drug (model drug substance). Their rheological properties were determined: flow curve, yield point, apparent viscosity. Moreover, a statistical analysis of factors (polymer type, polymer concentration, sterilization by autoclaving) was undertaken, and their impact on viscosity, yield point and area under flow curve was ascertained. Among this polymers, gels comprising Carbopol 974P were the most stable to sterilization conditions.

In situ study of gas transport through Al(OH)3 gels during AC processing

In this work the nature of gas transport through different Al(OH)3 gels (smut) formed during the AC electrograining process is characterized. A new in situ approach that combines small angle X-ray scattering (SAXS) with the electrochemical response is used to show that gas transport through the smut is different with and without additives. We conclude that gas transport occurs, predominantly, through temporary passageways when no additives are used and through permanent pores with additives, indicating a difference in the gel (smut) rheological properties in each case. Gas transport, through the smut, is therefore considered to be a phenomenon that depends on the electrolyte composition, which is expected to alter the gel properties. These changes in the gas transport away from the metal surface correlate with changes in the potential response of the system. The uniquely lower overpotential, associated with temporary passageways results in an etched-like morphology, suggesting that the gas permeability of the surface gel is a factor that affects the final pit morphology.

In Vitro Characterization of Chitosan Gels for Buccal Delivery of Celecoxib: Influence of a Penetration Enhancer

Celecoxib (Cx) shows high efficacy in the treatment of osteoarthritis and rheumatoid arthritis as a result of its high specificity for COX-2, without gastrolesivity or interference with platelet function at therapeutic concentrations. Besides of anti-inflammatory effects, Cx also has a potential role for oral cancer chemoprevention. For these conditions, oral administration in long-term treatment is a concern due to its systemic side effects. However, local application at the site of injury (e.g., buccal inflammation conditions or chemoprevention of oral cancer) is a promising way to reduce its toxicity. In this study, the in vitro characterization of mucoadhesive chitosan (CHT) gels associated to Azone® was assessed to explore the potential buccal mucosal administration of Cx in this tissue. Rheological properties of gels were analyzed by a rheometer with cone-plate geometry. In vitro Cx release and permeability studies used artificial membranes and pig cheek mucosa, respectively. Mucoadhesion were measured with a universal test machine. CHT gels (3.0%) containing 2.0% or 3.0% Az showed more appropriate characteristics compared to the others: pH values, rheology, higher amount of Cx retained in the mucosa, and minimal permeation through mucosa, besides the highest mucoadhesion values, ideal for buccal application. Moreover, the flux (J) and amounts of drug released decreased with increased CHT and Az concentrations. CHT gels (3.0%) associated with 2.0% or 3.0% Az may be considered potential delivery systems for buccal administration of Cx.

Rheological and textural studies of fresh and freeze-thawed native sago starch–sugar gels. I. Optimisation using response surface methodology

A three-factor–three-level Box–Behnken design was adopted to study the simultaneous effects of two compositional variables (6–8% sago starch and 25–35% sugar) and one processing variable (shearing speed of mixer at 20–50 rpm) on textural and rheological properties of gels. Analysis of variance (ANOVA) was performed to evaluate the potential interactive and quadratic effects between these variables. Sago starch and sugar levels both increased gel stiffness and viscoelasticity. Shearing, on the other hand, reduced gel stiffness and viscoelasticity. Ridge analysis was performed to estimate the values of these variables which maximised and minimised the textural parameters of hardness, gumminess, resilience, cohesiveness, and springiness. Pearson correlations among various rheological and textural properties of gels were studied. The processing conditions that contributed to an optimum gel setting were found at sago starch of level of 7.69%, sugar of 30.29%, and shearing speed of 45.86 rpm.

Effect of non-starch polysaccharides on the in vitro digestibility and rheological properties of rice starch gel

The starch digestibility and rheological properties of gels were evaluated in the presence of three non-starch polysaccharides (agar, xanthan gum and konjac glucomannan) with rice starch. Each polysaccharide was added to 30% (w/w) rice starch suspension at defined concentrations and starch gels were prepared. The extent of starch gel digestibility was determined by an in vitro method and rheological properties by a dynamic oscillatory test and a compression test. The added polysaccharides suppressed starch hydrolysis in the gels compared with the control, and a concentration dependency of this suppressive effect was observed. Adding agar and xanthan gum increased the storage shear modulus (G′) of starch gels, while adding konjac glucomannan decreased G′ values. The results indicate that the suppressive effect of non-starch polysaccharides on starch digestibility appears to be not only due to the rigidity of the gel, but also the interaction between starch and non-starch polysaccharides.

Mixtures of whey protein microgels and soluble aggregates as building blocks to control rheology and structure of acid induced cold-set gels

Whey proteins (WP) today offer an extremely high potential for innovative development of functional and nutritious food products. Acid cold-set gels present an interesting approach of gelation at low temperature upon acidification of preformed whey protein (WP) aggregates. In the present work, we aimed to demonstrate how structure and rheological properties of acid gels can be controlled by combining two types of WP aggregates with different structural and chemical properties. Whey protein microgels (WPM) and soluble aggregates (WPSA) were generated upon heating WP isolate in specific pH conditions and temperature, leading to Z-average hydrodynamic diameters close to 270 nm for WPM and 100 nm for WPSA. Mixtures of WPM and WPSA were prepared at different weight ratios ranging from 100% WPM to 100% WPSA. The total protein concentration was set to 4 or 8%wt. Acidification was performed at 40 °C by addition of 1%wt glucono-δ-lactone (GDL). Gelation was followed using turbidimetry and small deformation rheology as function of pH. Microstructures of the gel were investigated at different length scales using various microscopy techniques (CLSM, SEM, AFM). When the WPM/WPSA ratio decreased, the pH of gelation and the gel strength increased because of the different structure and chemical reactivity of the two types of WP aggregates. The final pH had a strong impact on the structure of the gels. When final pH decreased below pH 4.3, a structure change was suggested by turbidimetry measurements. This resulted in a non self-supporting gel or in a decrease of gel strength. For pH above 4.3, self supporting gel were obtained. The rheological properties of the gel could therefore be modulated depending on the properties of the building blocks used (WPM versus WPSA). Interestingly, the gel microstructures observed for WPM/WPSA mixtures or WPM were comparable to those of acidified skimmed milk gels ranging from coarse structures with clumps of aggregates or to homogeneous fine networks (WPSA only) that have been described for WP gels obtained upon direct heating at various pH.

Study the Rheological Properties of Abrasive Gel with Various Passageways in Abrasive Flow Machining

Abrasive flow machining (AFM) is a simple and efficient method to remove recasting layers making by wire electrical discharge machining (WEDM). However, conventional AFM methods have difficulty achieving uniform roughness of an axial distribution in circular hole polishing due to limited unitary axial motion of abrasive media. Therefore, this work develops mechanism designs for different passageways to obtain multiple flowing paths of abrasive medium, whose flowing behavior enhances polishing effectiveness by increasing the abrasive surface area and radial shear forces. The motion of the abrasive medium is studied by utilizing different mold cores, which mold shapes include the circular, hollow and helical passageway. The optimum design of the passageways is then verified using CFD-ACE+ software, numerical results indicate that passageway with six helices performed better in the uniform surface roughness than others’ do. Experimental results show that roughness deviation of six helices passageway of approximately 0.100 m Ra is significantly better than those on a circular passageway of around 0.1760 m Ra. Additionally, the six helices passageway is also superior to circular passageway in reducing roughness improvement rate (RIR) by roughly 87% compared with RIR 67.7% for the circular passageway.

Stress Relaxation of Acid-induced Milk Gels

The effects of the addition of sugar (sucrose) or salt (KCl/NaCl mixture) on the rheological properties of acid milk gels formed under different process and composition conditions were studied using an experimental design and surface response analysis. The variables evaluated were: sodium caseinate, whey protein concentrate, carrageenan, sucrose or KCl/NaCl concentration, and the mixing temperature of the components. The stress relaxation measurements were made within the linear viscoelasticity domain, and the data obtained were fitted to the generalized Maxwell model. Five parameters were obtained from the fitting: three elastic elements and two viscous elements. In addition, the denaturation process of whey protein with different solute concentrations was evaluated using differential scanning calorimetry. Denaturation temperature increased with increases in the solute concentrations, but enthalpy values did not change independent of solute type and concentration. The results showed that the elastic and viscous moduli increased with sucrose concentration, i.e., the gel network was reinforced, while the opposite occurred with the addition of the saline mixture. Increasing ionic strength of saline mixture and the process temperature were the more important effects with respect to the rheological properties of gels with added saline mixture. On the other hand, the biopolymer concentrations showed the most significant effects on the properties of gels with added sugar.

Effect of Sucrose on the Thermal and Rheological Properties of Mixed κ-Carrageenan and Gelatin Gels

Effect of Sucrose on the Thermal and Rheological Properties of Mixed κ-Carrageenan and Gelatin Gels