Effect of barley β-glucan concentration on the microstructural and mechanical behaviour of acid-set sodium caseinate gels

Effect of ultrasonic pretreatment on physicochemical characteristics and rheological properties of soy protein/sugar Maillard reaction products

Maillard reaction products (MRPs) of soybean protein isolate (SPI) and sugars (glucose and maltose) were prepared by heating in the aqueous dispersion at 95 °C for 15 min with ultrasonic pretreatment (ultrasonic power of 200 W) for 20 min. Effect of ultrasonic pretreatment on physicochemical characteristics and rheological properties of SPI/sugar MRPs was investigated. SPI/sugar MRPs prepared with ultrasonic pretreatment had higher degree of glycation (DG), lower browning and less compact tertiary conformation than that with non-ultrasonic pretreatment. Surface hydrophobicity (H0), particle size and rheological properties were measured by fluorescence spectrophotometry, laser particle size analysis and dynamic oscillatory rheometry, respectively. Glycation reduced H0 and particle size as well as weaken the gel network formed by the acidification of GDL. However, ultrasound increased H0 and decreased particle size. This is desirable for the formation of acid-induced gel structure. The ultrasonic pretreatments reduced/eliminate the weakening effect of glycation on the gel network of SPI/sugar MRPs, and even improved the gel properties.

Textural and Rheological Properties of Oat Beta-Glucan Gels with Varying Molecular Weight Composition

The impact of oat β-glucan concentration and molecular weight (MW) on gel properties was investigated. Mixed MW gels/viscous solutions at 3, 4, and 5% β-glucan with high molecular weight (HMW):low molecular weight (LMW) ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 were evaluated. The 100:0 and 50:50 gels had the lowest tan δ values. The 50:50 gels had the highest storage moduli (G'), whereas 100:0 solutions did not gel. Peak melting temperature (T_P) was highest for 0:100 gels and decreased with the addition of HMW β-glucan. Hardness, at 40% compression, increased with concentration, and 25:75 and 50:50 gels were hardest at each concentration. Ordered microstructure, apparent in 0:100 gels, diminished with HMW β-glucan addition. Glucose addition resulted in lower tan δ values and firmer, harder gels compared to gels without glucose. Thus, the textural properties and melting profiles of β-glucan gels can be manipulated by adjusting the ratios of molecular weight fractions or addition of sugar for different applications.

Morphology and mechanical properties of bicontinuous gels of agarose and gelatin and the effect of added lipid phase

This study examines the structural properties of binary and tertiary mixtures made of the cold-setting biopolymers agarose and gelatin and a lipid phase with solid or liquid-like viscoelasticity. The working protocol included the techniques of small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry and scanning electron microscopy, and theoretical modeling that adapted ideas of relating the morphology to the elastic modulus of synthetic polyblends and block polymers. The experimental setting was designed to encourage extensive phase separation in the binary gel of agarose and gelatin whose mechanical properties were rationalized on the basis of a bicontinuous blending law. The presence of two continuous phases allowed the slower-gelling component (gelatin) to exhibit favorable relative affinity for the solvent with increasing concentrations of the protein in the system. This is an unexpected outcome that contradicts the central finding of a single value of the p factor observed in the distribution of solvent between the continuous matrix and discontinuous inclusions of deswelled binary gels reported earlier in the literature. The incorporation of a lipid phase of effectively zero elastic modulus or in excess of 10(8) Pa in the composite aqueous gel weakens or reinforces the matrix accordingly. The elastic moduli and morphology of the tertiary blend were related to changing the relative phase volumes of components using analytical expressions of isotropically dispersed soft or rigid filler particles in a polymeric matrix.

Morphology of molecular soy protein fractions in binary composite gels

We investigate the structural properties of gels of binary mixtures of the three major soy protein fractions: 11S, 7S, and 2S. Gels are formed at 25 degrees C in the presence of glucono-delta-lactone and studied using a combination of dynamic rheology and scanning electron microscopy. The theological data was then modeled using a blending-law approach that yields insights into the solvent distribution between the gelled protein fractions and first-order reaction kinetics that follow the gelation process of the single fractions and their mixtures. Gelled mixtures of 11S and 7S yielded enhanced network strength with increasing solid content; in these gels, 50% more solvent partitioned into the 11S phase as compared to that in the 7S phase. In contrast, the addition of small-molecular-weight counterpart 2S to either 11S or 7S results in a catastrophic drop in the values of the overall strength of the mixture. The unexpected phase behavior has been rationalized on the basis of the high water-holding capacity of 2S; 450% more solvent partitions preferentially into the 2S phase as compared to that in the 11S phase. As the concentration of 2S is increased relative to that of 11S or 7S, it becomes the dominant phase and entraps the polymeric segments of 11S (or 7S), thus preventing them from becoming the structural knots of the gel. In addition to the solvent distribution in the gel, the rates of gelation differ markedly between 11S and 2S (with the 11S rate of gelation being up to 2 orders of magnitude greater); a fixed 11S concentration, the rate of gelation decreases with increasing amounts of 2S, further confirming that the latter essentially becomes the dominant phase in the composite gel.

Phase model interpretation of the structural properties of two molecular soy protein fractions

The structural properties of mixtures of two molecular soy fractions, 11S (glycinin) and 2S, were investigated in the presence of glucono-delta-lactone (GDL) during an isothermal run at 25 degrees C for 1500 min. Analytical methodology included small-deformation dynamic oscillation, visual observations, scanning electron microscopy, and blending-law modeling. The aim of the work was to identify the state of phase separation and the pattern of solvent distribution between the two constituent polymers. It was found that the high molecular weight distribution of 11S supported rapid kinetics of structure formation, with this continuous matrix being concentrated and, hence, further reinforced in the presence of small additions of 2S. Blending-law modeling suggested that 2S was able to retain disproportionate volumes of solvent within its phase. A consequence of such property was that high additions of 2S leading to equal concentrations of the two molecular fractions in the blend resulted in a catastrophic drop in the values of the overall network strength. This behavior is rather unexpected for the structural properties of a phase-separated system, and it has been rationalized on the basis of the high water-holding capacity of the small molecular weight fraction. 2S entraps in its phase the polymeric segments of glycinin, which are then unable to become structural knots of a cohesive three-dimensional morphology observed in single 11S preparations.