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Thermal denaturation of α-lactalbumin and β-lactoglobulin in cheese whey: effect of total solids concentration and pH

Published online by Cambridge University Press:  01 June 2009

Robyn M. Hillier ,
Richard L. J. Lyster  and
Gordon C. Cheeseman
Robyn M. Hillier
Affiliation:
National Institute for Research in Dairying, Shinfield, Beading, RG2 9AT
Richard L. J. Lyster
Affiliation:
National Institute for Research in Dairying, Shinfield, Beading, RG2 9AT
Gordon C. Cheeseman
Affiliation:
National Institute for Research in Dairying, Shinfield, Beading, RG2 9AT
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Summary

Measurements of residual native protein remaining after heat treatment of cheese whey have been made using quantitative polyacrylamide gel electrophoresis. The results have been expressed in terms of kinetic constants. The effect of concentration was investigated up to 3 times the normal total solids content, dialysis treatments were used to study the effect of non-protein constituents, and the effect of pH was studied at pH 4, 6 and 9. The results indicated that increased total solids (TS) concentration slowed the denaturation of β-lactoglobulin A and B (β-lg A, β-lg B) but hastened the denaturation of α-lactalbumin (α-la). However, increased lactose concentration slowed the denaturation of both α-la and β-lg, perhaps by preventing formation of heat-induced complexes. Increased Ca concentration, up to 0.4 mg/ml, tended to slow the denaturation of both proteins, but further increase in Ca up to 0.9 mg/;ml produced little effect. The rate of denaturation of both α-la and β-lg was slower at pH 4 than at pH 6 or 9, and was probably slowest at the isoelectric point. However, not all the changes associated with pH could be explained in terms of net molecular electrostatic charge. The genetic variants of ′β-lg showed different heat stabilities – below 90 °C β-lgA was more stable than β-lgB, but above 90 °C the situation was reversed at all TS concentrations, and pH 6. However, at pH 4 and 9, °-lgA was less stable than °-lgB over the entire temperature range at normal concentration.

Type
Original Articles
Information
Journal of Dairy Research , Volume 46 , Issue 1 , January 1979 , pp. 103 - 111
Copyright
Copyright © Proprietors of Journal of Dairy Research 1979

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