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Relationship between physicochemical properties of proteins and their foaming characteristics Townsend, Althea-Ann E.


The relationship between the foaming characteristics of proteins and some of their physicochemical properties in bulk solution were examined. The physico-chemical properties which were investigated in relation to foaming were hydrophobicity, charge density, secondary structure, molecular flexibility, dispersibility, viscosity and surface tension, Eleven, model proteins, (ribonuclease, ovomucoid, trypsin, lysozyme, pepsin, ovalbumin, conalbu-min, bovine serum albumin., K-casein, β-lactoglobulin, β-casein) and eight food proteins.(soy, pea, sunflower and canola isolates, pro-pulse, Promine-D, whole casein, acid solubilized gluten) were used. It was found that the average hydrophobicity of proteins could be measured using cis-parinaric acid as a probe of the hydrophobic regions, after the samples had been uncoiled by heating for 1.0. min at 100°C in the presence of 1.5% sodium dodecyl sulphate. Hydrophobicity measured in this way showed a significant linear correlation (r = 0.820, P <0.01 ) with the calculated average hydrophobicity values of Bigelow. Two regression equations.were generated, which accounted for approximately 77% of the variability in the foaming capacities of the proteins; one included hydrophobicity and dispersibility and the other involved hydrophobicity and viscosity as the independent variables. High hydrophobicity and viscosity, and moderate dispersibility were associated with optimum foaming capacity. Although charge density influenced the foaming capacity of proteins its role in determining this property seemed to be a minor one. Highest foaming capacity was exhibited by the most flexible proteins. There was a significant negative relationship (r =-0.726, P<0.01) between foam stability and the reciprocal charge density. This indicated that electrostatic repulsion between protein molecules had an important destabilizing effect on foams. It was demonstrated that hydrophobicity plays an important role in determining the foaming behaviour of protein solutions. Unlike, emulsification, which is dependent on surface hydrophobicity, the hydrophobicity of the uncoiled protein molecule is important for foaming.

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