19 research outputs found
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Determination of practically significant differences in the sensorily perceived consistency of semi liquid foods
The consistency of commercial salad dressing, chocolate pudding and mustard samples before and after controlled disruption was assessed by squeezing flow viscometry and evaluated sensorily by an untrained panel. The instrumental parameters were the apparent stress at 1.5 and 1.0 mm height and the apparent residual stress after 60 and 120 s relaxation (at 1.0 mm height). The panelists were asked to identify the sample(s) with the stronger consistency in a triangular test. The percent correct identifications was plotted against the difference in the magnitude of the instrumental parameters and their ratios. The scatter of these plots suggests that the effective stimulus for consistency perception was primarily the overall resistance to deformation or flow and to a much lesser extent to more subtle rheological characteristics like the ‘degree of solidity\u27. In the range of consistencies examined, the detection thresholds were on the order of 0.5-0.7 kPa and 0.4-0.6 kPa at 1.0 and 1.5 mm height, respectively. They corresponded to stress ratios on the order of 0.75-0.85. Results of this kind will enable setting objective standards for the consistency of commercial semi liquid foods and tolerance margins to deviations from them
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Influence of glycerol and sorbitol on thermally induced droplet aggregation in oil-in-water emulsions stabilized by beta-lactoglobulin
The influence of polyol cosolvents (glycerol and sorbitol) on the flocculation stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was examined. Salt (150 mM NaCl) and polyols (0–40 wt%) were added to n-hexadecane oil-in-water emulsions stabilized by β-lactoglobulin (β-Lg, pH 7.0) either before or after isothermal heat treatments (30–90 °C for 20 min). When salt was added to emulsions before heat treatment, appreciable droplet flocculation was observed below the thermal-denaturation temperature of the adsorbed β-Lg (Tm∼70 °C), and more extensive flocculation was observed above Tm. On the other hand, when salt was added after heat treatment, appreciable droplet flocculation still occurred below Tm, but little flocculation was observed above Tm. Addition of cosolvents to the emulsions increased the temperature where extensive droplet flocculation was first observed when they were heated in the presence of salt, which was attributed to their ability to increase Tm and to reduce the droplet collision frequency, with sorbitol being more effective than glycerol. Our results are interpreted in terms of the influence of the cosolvents on protein conformational stability, protein-protein interactions and the physiochemical properties of aqueous solutions. This study has important implications for the formulation and production of protein stabilized oil-in-water emulsions for industrial applications, such as foods, pharmaceuticals and cosmetics
Comparison of Physicochemical and Functional Properties of Chicken and Duck Egg Albumens
ABSTRACT The aim of this research was to investigate the physicochemical and functional properties of fresh and pasteurized chicken and duck egg albumens. The results showed that pasteurization of both chicken and duck albumens significantly decreased (p≤0.05) viscosity, but had no impact (p>0.05) on pH or free sulfhydryl groups. Chicken albumen was shown to have higher (p≤0.05) foam expansion, but lower (p≤0.05) foam stability than duck albumen. Pasteurization decreased (p≤0.05) the foam expansion of both albumens while decreasing (p≤0.05) the foam stability only of duck albumen. Investigation of the gel properties showed that duck albumen has greater hardness and lower expressible water (p≤0.05) than chicken albumen. Pasteurization increased the hardness and decreased the expressible water of both the chicken and duck albumen gels. This study suggests that the superior gel properties of duck albumen offer potential approaches to improving the quality of gel food products
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Inhibition of droplet flocculation in globular-protein stabilized oil-in-water emulsions by polyols
The influence of neutral cosolvents (polyols) on the stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was investigated. Glycerol (0–40 wt%) and sorbitol (0–35 wt%) were added to n-hexadecane oil-in-water emulsions stabilized by β-lactoglobulin (β-lg, pH 7.0, 150 mM NaCl), either before or after incubation at 30 °C for 24 h. The stability of the emulsions to flocculation and creaming improved when neutral cosolvents were added, with the effectiveness of the cosolvents depending on their type, concentration and time of addition. Emulsion stability was better for sorbitol than glycerol, improved with increasing cosolvent concentration, and was better when the cosolvents were added immediately after homogenization than when they were added 24 h later. The influence of the cosolvents on emulsion stability is interpreted in terms of their effect on the conformation and interactions of the adsorbed proteins, as well as on the droplet–droplet collision frequency. This study has implications for the development of protein stabilized oil-in-water emulsions for utilization in industrial products
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Impact of cosolvents (polyols) on globular protein functionality: Ultrasonic velocity, density, surface tension and solubility study
The objective of this study was to understand how cosolvents influence the molecular and functional properties of globular proteins in aqueous solutions. The ultrasonic velocity, density and adiabatic compressibility of cosolvent solutions (0–50 wt% sorbitol or glycerol) were measured in the absence and presence of a globular protein (1 wt% β-lactoglobulin) at 30 °C. These measurements were used to calculate the partial specific apparent volume and adiabatic compressibility of the protein. The protein\u27s volume decreased and its compressibility increased in the presence of high cosolvent concentrations, which were attributed to changes in the properties of the protein interior and solvation layer. Sorbitol was more effective than glycerol at decreasing the protein volume at high cosolvent concentrations, which may be because glycerol has some surface activity and may therefore accumulate around hydrophobic regions on the protein surface. Our data were used to account for the observation that sorbitol is more effective than glycerol at increasing the thermal stability and self-association of the β-lactoglobulin. A better understanding of the influence of protein–cosolvent–solvent interactions on the functionality of globular proteins may facilitate the design of protein-based products
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Modulation of thermal stability and heat-induced gelation of -lactoglobulin by high glycerol and sorbitol levels
The influence of glycerol and sorbitol on the thermal stability and heat-induced gelation of β-lactoglobulin (β-lg) in aqueous solutions was investigated. The thermal stability of β-lg was characterized by measuring the thermal denaturation temperature (Tm) using differential scanning calorimetry, while its gelation properties were characterized by measuring the gelation temperature (Tgel) and final gel rigidity (G∗) using dynamic shear rheology. All experiments were carried out using aqueous solutions containing 10% (w/w) β-lg, glycerol (0–70% w/w) or sorbitol (0–55% w/w), and 5 mM phosphate buffer (pH 7.0). No salt was added to these solutions so that there was a relatively strong electrostatic repulsion between the protein molecules, which usually prevents gelation. When the cosolvent concentration was increased from 0% to 50%, Tm increased from 74 to 86 °C for sorbitol, but only from 74 to 76 °C for glycerol, which indicated that sorbitol was much more effective at stabilizing the native state of the globular protein than glycerol. Protein solutions containing sorbitol (0–55%) did not form a gel after heating, but those containing glycerol formed gels when the cosolvent concentration exceeded about 10%, with G∗ increasing with increasing glycerol concentration. We attribute these effects to differences in the preferential interactions of polyols and water with the surfaces of native and heat-denatured proteins, and their influence on the protein–protein collision frequency
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Impact of cosolvents on formation and properties of biopolymer nanoparticles formed by heat treatment of beta-lactoglobulin-pectin complexes
The purpose of this study was to determine the influence of neutral cosolvents on the formation and properties of biopolymer nanoparticles formed by thermal treatment of protein-polysaccharide electrostatic complexes. Biopolymer particles were formed by heating (85°C, 20 min) an aqueous solution containing a globular protein (β-lactoglobulin) and an anionic polysaccharide (beet pectin) above the thermal denaturation temperature (Tm) of the protein under pH conditions where the biopolymers formed electrostatic complexes (pH 5). The impact of two neutral cosolvents (glycerol and sorbitol) on the self-association of β-lactoglobulin and on the formation of β-lactoglobulin-pectin complexes was examined as a function of solution pH (3-7) and temperature (30-95°C). Glycerol had little impact on the pH-induced self-association or aggregation of the biopolymers, but it did increase the thermal aggregation temperature (Ta) of the protein-polysaccharide complexes, which was attributed to its ability to increase aqueous phase viscosity. Sorbitol decreased the pH where insoluble protein-polysaccharide complexes were formed, and greatly increased their Ta, which was attributed to its ability to increase Tm, alter biopolymer-biopolymer interactions, and increase aqueous phase viscosity. This study shows that neutral cosolvents can be used to modulate the properties of biopolymer nanoparticles prepared by thermal treatment of protein-polysaccharide electrostatic complexes