Conformational Changes of αs-Casein by Heating

Conformational changes of α_s-casein by heating were investigated by measuring ultraviolet difference spectra. The ultraviolet difference spectra at elevated temperature against 5.5°C were measured in various ionic strengths and pHs. Thermal effects of the difference spectra were cancelled by comparing with the spectra of model compounds such as lysozyme and ribonuclease, and the blue shift of α_s-casein spectra was observed at above 30°C in these all experimental conditions. This shift was considered to mean unfolding of the α_s-casein molecule. The aggregation of α_s-casein was observed above ionic strength of 0.4 by heating. These heat-induced changes were reversible until the aggregation was observed.     

Can Reptile Embryos Influence Their Own Rates of Heating and Cooling?

Previous investigations have assumed that embryos lack the capacity of physiological thermoregulation until they are large enough for their own metabolic heat production to influence nest temperatures. Contrary to intuition, reptile embryos may be capable of physiological thermoregulation. In our experiments, egg-sized objects (dead or infertile eggs, water-filled balloons, glass jars) cooled down more rapidly than they heated up, whereas live snake eggs heated more rapidly than they cooled. In a nest with diel thermal fluctuations, that hysteresis could increase the embryo’s effective incubation temperature. The mechanisms for controlling rates of thermal exchange are unclear, but may involve facultative adjustment of blood flow. Heart rates of snake embryos were higher during cooling than during heating, the opposite pattern to that seen in adult reptiles. Our data challenge the view of reptile eggs as thermally passive, and suggest that embryos of reptile species with large eggs can influence their own rates of heating and cooling.     

Improvement of the Surface Functional Properties of β-Lactoglobulin and α-Lactalbumin by Heating in a Dry State

Controlled heating in a dry state greatly improved the surface functional properties of whey proteins (β-lactoglobulin and α-lactalbumin). Although whey proteins were completely insolubilized by heating at 80°C in an aqueous solution, their solubility was kept even after heating at 80°C in a dry state (7.5% moisture content) for 5 days. The surface hydrophobicity of α-lactalbumin was increased during the dry-heating, while that of β-lactoglobulin was decreased. In addition, the fluorescence spectra excited at 280 nm of dry-heated whey proteins suggested the significant conformational changes. High-performance gel chromatography showed that a considerable amount of soluble aggregates was formed in the dry-heated β-lactoglobulin, while a small amount of soluble aggregate was observed in the dry-heated α-lactalbumin. The foaming properties of dry-heated whey proteins were increased to about 3 times that of untreated proteins. The emulsifying properties of dry-heated whey proteins were also increased, compared to untreated proteins, although a slight decrease in the emulsion stability was observed in dry-heated β-lactoglobulin. The improvement of the surface properties seemed to come from the partial unfolding suitable for the formation of foam film and the entrapment of oil droplets.     

Viscoelastic and Thermal Properties of Collagen–Xanthan Gum and Collagen–Maltodextrin Suspensions During Heating and Cooling

The purpose of this work was to investigate the viscoelastic properties of aqueous suspensions of crude collagen powder extracted from bovine hides and nonsubmitted to the hydrolysis reaction that leads to gelatin. The studied variables included the collagen concentration and the addition of xanthan gum or maltodextrin at varied concentrations during heating/cooling of the mixtures. Differential scanning calorimetry thermograms showed that the addition of polysaccharides decreased the endothermic peak areas observed at the denaturation temperature of collagen. The rheological properties of the pure collagen suspensions were highly dependent on concentration: 4% and 6% collagen suspensions presented a great increase in the storage modulus after heating/cooling, whereas for concentrations of 8% and 10% G′ decreased during heating and did not recover its original value after heating/cooling. The frequency sweeps showed that the thermal treatment was responsible by the strengthening of the interactions that formed the polymer network. Addition of 0.1% xanthan gum to collagen suspensions increased the gel strength, especially after heating/cooling of the system, whereas increasing gum concentration to 0.3% resulted in a weaker gel, which could indicate thermodynamic incompatibility between the biopolymers. Mixtures of collagen and maltodextrin resulted in more fluid structures than those obtained with pure collagen at the same collagen concentration and the range of temperatures in which these mixtures behaved as a gel decreased with increasing concentrations of both collagen and maltodextrin, suggesting incompatibilities between the biopolymers.     

Time–Space Evolution of the Parameters of Turbulent Density Fluctuations During Pulsed EC Heating of the Plasma at the L-2M Stellarator

Plasma Physics Reports - The study is continued of the temporal changes of the parameters of turbulent plasma density fluctuations during multi-pulse electron cyclotron (EC) heating of the plasma...