Small Strain Oscillatory Tests Research Articles

Rheological properties of arabinogalactan solutions related to the carbohydrate composition of different legumes

The aim of this study was to elucidate chemical structures and rheological properties of arabinogalactans (AGs) isolated from three legumes including black gram (BG), great northern bean (GNB), and California small white bean (CSWB). The ratio of galactose to arabinose (G/A) in three legumes increased in the order of BG > GNB > CSWB. The rheological measurements of 1-5% (w/v) AG solutions revealed Newtonian and non-Newtonian flow behaviors. BG exhibited yield stress, indicating plastic behavior. Small-amplitude oscillatory tests indicated viscoelastic properties of BG, GNB, and CSWB ranging from solid-like, paste-like, and liquid-like behaviors, respectively. Small-strain oscillatory tests were conducted to assess the structure recovery of the AGs after pre-shearing. G″ values of BG and GNB increased, but those of CSWB remained constant after shearing. These results suggest that the chemical structures of the AGs, particularly their G/A ratios, influence their rheological properties.

Emulsion-filled gels of soy protein isolate for vehiculation of vitamin D3: Effect of protein solubility on their mechanical and rheological characteristics

The aim of this study was to develop heat-induced gels of soy protein isolate (SPI) filled with Brazil nut oil emulsions encapsulating vitamin D3 (VD3). Before gelation, dispersions produced with different SPI concentrations (11–15%, w/w) were subjected to different pretreatments (manual mixing or mechanical stirring at 800 rpm for 10, 20, and 30 min) and had their protein solubility quantified. The application of mechanical stirring increased the solubility of proteins and decreased the average particle size, affecting the microstructure (observed by confocal laser scanning microscopy) and rheological properties (evaluated by uniaxial compression and small strain oscillatory tests) of the heat-set gels. The incorporation of emulsions (produced with Brazilian nut oil) into gels formed emulsion filled gels (EFGs), which presented higher Young's moduli and σH in comparison to non-filled gels (NFGs), indicating that the oil droplets were active within the matrices. The properties of EFGs subjected to small strain oscillatory tests, varied with the pretreatment conditions and SPI concentrations, highlighting the high influence of protein solubility, matrix inhomogeneities, and droplet clustering for determining the properties of such complex systems. Also, the heat-induced emulsion-filled gels of SPI produced were effective in protecting VD3, presenting good retention after 30 days of storage under refrigeration, and represent promising alternative for the production of future food gelled products.

Rheological characterization of tuna myofibrillar protein in linear and nonlinear viscoelastic regions

The gelation characteristics of myofibrillar proteins are indicative of the ultimate texture of fish products. This study investigated the impact of pH (5.6–7.0) on viscoelastic properties of tuna myofibrillar proteins using dynamic oscillatory rheometer under both small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS). Using small-strain oscillatory tests, the rheological properties during gelling were quantified. Results indicated that protein denaturation and gel formation were pH dependent. LAOS tests indicated that pH strongly affected the structure of the myofibrillar proteins system as shown by deformation of the nonlinear stress response curve. Increasing pH produced an increasingly strong, more stable network. All non-linear behaviors increased with increasing strain in a similar manner, suggesting a general mechanism responsible for strain effects that was similar for non-linear and fracture behavior. Furthermore, pH also appeared to influence the water-holding capacity and surface hydrophobicity.

The shear rheology of bread dough: modeling

The mechanics and rheology of the two-regime shear flow behaviour of bread dough was explored. Small-strain oscillatory measurements revealed that storage and loss moduli data as a function of applied frequency fit power law relations, with the exponent p ∼ 0.31. A Lodge-type model with a power law memory function was then investigated for shear flow, where relaxation parameters were derived from small-strain oscillatory tests. The model implied the response to steady shear may be described as a product of shear rate to the exponent p and a function of strain, which is confirmed by experimental observations. The soft-solid rheological behaviour of bread dough under steady shear deformation was then analysed over a range of shear rates (0.1–20 s − 1). Initially, stress was over-predicted in the reconstruction of the data, and the application of a damage function to the model was considered since the material fractures under shear strains ∼20. The damage term was found to be a function of strain over the complete range of shear rates. The transition of dough from solid-like to liquid-like behaviour is discussed, following the damage reduction factors rapidly reducing to zero post material fracture, which suggested a loss of elasticity in the dough. A simple integral-type model resulted for the prediction of the shear rheology of bread dough in the solid-like regime, with generalised Newtonian viscous behaviour predicted for shear flows following material fracture. Further analysis on local strain behaviour in more complex shearing geometry, such as tube flow, is required.

Gelation of protein isolates extracted from tilapia light muscle by pH shift processing

The gelation properties of protein isolates extracted from tilapia muscle with acid and alkali-aided processing were compared to washed tilapia muscle. Gels were prepared with and without the addition of 2% NaCl (w/w) slightly above neutral pH and gelation properties and gel quality were determined using various procedures. Hardness and elasticity of gels as assessed by torsion testing was improved using 2% NaCl (w/w) compared to treatments without salt. Small strain oscillatory testing showed that storage modulus (G′) of gel pastes prior to thermal gelation was significantly higher in the absence of salt, while smaller differences were seen after thermal gelation. Small strain oscillatory tests demonstrated a different gel forming mechanism for acid and alkali treated proteins compared to washed muscle. Fold tests demonstrated that acid treated proteins and washed muscle had significantly lower gel quality compared to alkali treated proteins. Addition of salt in gels improved gel water-holding capacity for acid and alkali treated proteins. Overall, the acid treated proteins exhibited poorer gelling ability compared to alkali treated proteins. Total content of SH-groups was measured before and after gelation and S–S bonding did not explain the difference in gel forming ability of different treatments. The results indicate that the alkali-aided process can be used to produce high quality protein gels from tilapia muscle suitable for manufacturing of imitation seafood products.

Mechanical properties of wood flour/HDPE/ionomer composites

The structure and mechanical properties of wood flour composites with HDPE/ionomer blends as matrices were studied at a fixed wood loading of 60% by weight. It was found that toughness and strength properties of the composites can be improved significantly by adding ionomers of different types and contents. The enhancement in the interfacial interaction was observed through short-time creep analysis. The interfacial interaction and the structure of the matrix phase were characterized through the melting behavior using differential scanning calorimetry (DSC) and with small strain oscillatory tests on the melts using a Dynamic Mechanical Analyzer. Both the sodium and zinc ionomers were found to be immiscible with the HDPE in matrix. The immiscible characteristic was correlated with the interfacial load transfer efficiency as revealed by the creep tests.

Effects of pork collagen on thermal and viscoelastic properties of purified porcine myofibrillar protein gels

The objectives of this study were to examine the thermal, water-binding and viscoelastic properties of mixed protein systems containing purified myofibrils from porcine semimembranosus (MP) and pork collagen (PC) during gelation and subsequent cooling. MP:PC mixtures (100:0, 90:10, 80:20, 70:30, 60:40, 50:50) normalized to 4% protein were evaluated. No significant differences in thermal characteristics of these mixtures could be detected using differential scanning calorimetry. A primary peak was observed near 66 °C. Using small-strain oscillatory testing, the rheological properties during gelling and cooling were quantified. Storage modulus ( G′) increased upon heating for all treatments, but the rate of gel firming and the G′ value at 85 °C were significantly lower ( P<0.05) as PC was added to the mixed protein system. Upon cooling, gels revealed a significantly lower ( P<0.05) rate of gel firming and significantly lower ( P<0.05) G′ value at 5 °C in samples with 20% inclusion of PC and higher. Addition of PC yielded a significant linear ( R 2=0.65; P<0.01) increase in the water-holding capacity (WHC) of the gels, indicating that the matrix formed in MP:PC gels had a greater ability to entrap water than that of the control MP gels. The inclusion of 10% PC resulted in gels with significantly higher ( P<0.05) WHC and similar firmness when compared with gels comprised of MP as the only protein source.

Vane Sensor System in Small Strain Oscillatroy Testing

Abstract To overcome difficulties (slip, sample disturbance) associated with traditional sensors, a semi-empirical method was developed to allow the use of a 4-bladed vane sensor in small strain oscillatory testing. It was assumed that the vane sensor acted as a bob with an acting radius, RV, different from the actual radius of the vane (0.02005 m). To solve for RV, the complex modulus obtained using a concentric cylinder sensor from reference viscoelastic fluid, was set equal to the complex modulus equation for vane sensor. RV values were grouped into three phase shift ranges from 5° to less than 16°, from 16° to less than 60°, and from 60° to 90° and they were 0.01883, 0.01869, and 0.01850 m, respectively. These values were used in the calculation of viscoelastic properties of eight commercial food products, which resulted in complex modulus values within 15% of those obtained using a concentric cylinder sensor. Results showed that this particular vane and cup system can be used to directly measure the storage and loss moduli of viscoelastic material and phase shift within the upper frequency value of 6.28 rad/s. Above 6.28 rad/s, there is an inconsistency in phase shift angles measured using vane method. This method is ideal for testing thixotropic food systems because disturbance is minimal during sample loading, giving more accurate viscoelastic measurements.

Effect of concentration on rheological properties of acid-hydrolyzed amylopectin solutions

Rheological properties are sensitive to variations in molecular structure and they are useful in developing structure–function relationships for systems of polysaccharides in solution. Intrinsic viscosities of acid-hydrolyzed Amioca starches in 90% DMSO/10% water were determined using a modified approach for polyelectrolytes. Double logarithmic plots of specific viscosity, η sp, against coil overlap parameter, c[ η], were made and trends in both the dilute and concentrated regimes were found to be similar to those seen with other polysaccharides. Dynamic frequency sweeps indicated that all acid-hydrolyzed starches in 90% DMSO/10% water exhibited dilute solution or liquid-like behavior with G″ higher than G′. A contradiction in classification of 6–12% starch dispersions was found with shear tests (concentrated) and small strain oscillatory tests (dilute).

Physical Properties and Gelation Behavior of a Low-Amylopectin Maize Starch and Other High-Amylose Maize Starches

This paper examines the effect of changes in fine structure due to hybrid breeding on gel formation and gel properties of high-amylose maize starches. Both small-strain oscillatory testing and uniaxial-compression testing ranked G′ and texture/strength, respectively, in the same order of HYLON® V starch <HYLON® VII starch <low-amylopectin starch (LAPS). The starch gels became more rigid and stronger as amylose content of the hybrids increased from HYLON V starch to LAPS. It was also noted in these studies that LAPS had the quickest onset of gelation and HYLON V starch had the slowest. The effect of preparation temperature on gel properties was also studied by cooking high-amylose starches at 250 °, 270 °, 290 °, 310 °, 330 °F in a mini-jet cooker with minimal steam. Temperature of jet cooking had an impact on the rate of sol-to-gel transformation of the starches, which in turn influenced the final gel properties. All three hybrids were strongest (highest fracture stress and strain values) when prepared at 270 °F. HYLON V had the narrowest cooking tolerance forming self-supporting gels from 270 ° to 310 °F, while LAPS was the most robust, forming acceptable gels throughout the range of temperatures tested.

Optimization of an Aqueous Extraction Process for Flaxseed Gum by Response Surface Methodology

Aqueous extraction of hydrocolloidal gum from flaxseed was optimized using response surface methodology. Extraction temperature (25-100°C), pH (2.0-7.0) and water:seed ratio (6.0-20.0) were the factors investigated with respect to yield, apparent viscosity and protein content of the final gum extracts. Temperature and pH were found to have a significant influence on both yield and quality of the extracted crude gum while the water:seed ratio had only minor effects. Optimum conditions for the extraction were a temperature of 85-90°C, a pH 6.5-7.0 and a water:seed ratio of 13. In addition, steady shear and small strain oscillatory tests on aqueous dispersions of gums, extracted under various conditions, were conducted to assess the impact of extraction conditions on the rheological properties of the flaxseed gum preparations.