Thermal Analysis of Food Proteins

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Chemical characterization and functionality assessment of oat protein fractions

Protein fractions (albumins, globulins, prolamins, and glutelins) were prepared from oat seeds (variety Sentinel). Column chromatography on Sephacryl S-200 revealed that the four solubility fractions had unique polypeptide compositions and there was little cross contamination among the fractions. Isoelectric focusing on polyacrylamide gels resolved the fractions into a large number of bands covering a wide pH range. Differential scanning calorimetric studies showed that albumins and globulins had an endothermic peak at 87 and 110 °C, respectively, while prolamins and glutelins had no thermal response. Some functional properties of the solubility fractions were determined to assess the potential use of oat proteins as a food ingredient. Some fractions had high emulsifying, fat-binding, and water hydration capacities, and the albumins also had excellent foaming properties.link_to_subscribed_fulltex

Effects of medium and chemical modification on thermal characteristics of β-lactoglobulin

The thermal properties of β-lactoglobulin (β-LG) were studied by differential scanning calorimetry (DSC) under different medium conditions. pH, neutral salts, protein perturbants, and polyols all affected the DSC characteristics of β-LG. Acylation with fatty acids also changed the thermal properties, particularly peak width at half-height. The results suggest that the structural stability of β-LG is controlled by non-covalent forces, particularly electrostatic and hydrophobic interactions. Disulfide bonds did not contribute to the thermal response of β-LG. Fatty N-acylamino acids caused marked increases in thermal stability and decreases in denaturation enthalpy, and additional peaks were observed in the presence of some palmiloyl derivatives. © 1996 Akadémiai Kiadó.link_to_subscribed_fulltex

Study of thermal denaturation of oat globulin by ultraviolet and fluorescence spectrophotometry

Thermal denaturation of dilute (<0.05%) oat globulin solutions at high ionic strength was studied by ultraviolet (UV) and fluorescence spectrophotometry. Ultraviolet spectra show a significant red shift of absorption maximum when the protein was heated at 110°C. Second-derivative and difference-derivative spectra suggest exposure of tryptophan and tyrosine residues in the heated samples. Fluorescence emission spectra show a significant blue shift, indicating protein unfolding. When 1% oat globulin was heat aggregated and fractionated into soluble and insoluble fractions, UV and fluorescence spectra indicate no marked protein unfolding in the soluble fraction but extensive denaturation in the insoluble aggregates. The soluble fraction had significantly higher surface hydrophobicity than the soluble fraction and the unheated protein.link_to_subscribed_fulltex

Physicochemical properties of alkali-treated oat globulin

Oat globulin dispersions (10% w/v) were incubated at an initial pH of 9.8 at 25, 37, and 55°C over a period of 96 h. Turbidity increased at 25 and 37°C with the formation of insoluble aggregates and decreased at 55°C with little precipitation. The free SH content decreased progressively with time, while the surface hydrophobicity was increased at 25°C and decreased at 37°C. Differential scanning calorimetry showed progressive increases in denaturation temperature and decreases in width at half-peak height. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated formation of soluble aggregates at 55°C and degradation of oat globulin polypeptides at 25 and 37°C, possibly due to proteolysis by protease(s) coextracted with the protein. No significant racemization of amino acids was observed in the alkali-treated protein.link_to_subscribed_fulltex

Detection of incubator reject eggs by differential scanning calorimetry

A method to detect the presence of incubator reject (IR) eggs in fresh egg white by differential scanning calorimetry (DSC) was described. The transition temperature of denaturation (Td) of ovalbumin of fresh shell egg white was observed by DSC to be 83°C. After eggs had been in an incubator (38°C) for at least 4 days, the ovalbumin changed to S-ovalbumin and the denaturation temperature (Td) of the endotherm peak increased to 91°C. Incubation for two days resulted in the transformation of ovalbumin (Td 83°C) into an intermediate state (Td 87°C). In processed egg white (EW), thermograms showed only partial transformation of ovalbumin to the intermediate state which appeared as a split peak or shoulder with a Td of 87°C. In IR eggs, the ovalbumin was completely transformed into S-ovalbumin. In mixtures of egg white from fresh and incubator reject eggs, DSC could detect the two species as a split ovalbumin peak with Td 83°C and Td 91°C. Adulteration of egg-white products with as little as 7% incubator rejects can be detected by DSC. © 1992.link_to_subscribed_fulltex

Thermal gelation of oat globulin

The thermal gelation properties of oat globulin were studied under different conditions of temperature, protein concentration, pH, and ionic strength. Differential scanning calorimetry shows that oat globulin heated under conditions inducing gelation was not extensively denatured and exhibited highly cooperative transition characteristics. The chemical forces involved in gel formation were investigated by measuring the gel hardness under the influence of neutral salts, reducing agents, denaturants, and water-miscible solvent. Some fatty acid salts were effective in improving the gelling property of oat globulin near neutral pH.link_to_subscribed_fulltex

Effect of gamma irradiation on the physicochemical and functional properties of frozen liquid egg products

Frozen egg products (egg white and egg yolk) were subjected to gamma irradiation at pasteurization dosages of 1-4 kGy. The apparent viscosity of frozen egg yolk was significantly (p ≤ 0·05) decreased by radiation treatment. Polyacrylamide gel electrophoretic patterns and differential scanning calorimetric profiles of the egg white proteins were not affected by irradiation. The functional properties (foaming, emulsifying and gelling) of the egg products were generally not significantly (p > 0·05) affected by irradiation, or slightly decreased. Angel food cakes prepared with irradiated frozen egg white had increased cake volume, and mayonnaise prepared with irradiated frozen egg yolk had increased stiffness and stability. The results suggest that irradiation may be used as an alternative procedure for pasteurizing frozen liquid egg products. © 1993.link_to_subscribed_fulltex