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Interaction between heated κ-casein and β-lactoglobulin: predominance of hydrophobic interactions in the initial stages of complex formation

Published online by Cambridge University Press:  01 June 2009

Zahurul Haque  and
John E. Kinsella
Zahurul Haque
Affiliation:
Institute of Food Science, Cornell University, Ithaca, NY 14853, USA
John E. Kinsella
Affiliation:
Institute of Food Science, Cornell University, Ithaca, NY 14853, USA
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Summary

Mixtures of κ-casein and β-lactoglobulin (β-lg) were heated at 70 °C in 20 mM-imidazole buffer, pH 6·8 containing 20 mM-EGTA. Aggregation of the κ-casein/β-lg mixture occurred within 90 s and susceptibility to hydrolysis by chymosin decreased significantly within 180 s even though covalent interaction was not detected until after 4000 s. UV-absorbance indicated initial structural destabilization of the heated κ-casein/β-lg mixture followed by a return ( > 350 s) to a spectrum comparable to the native state, indicating molecular rearrangement. Apparent hydrophobicity of κ-casein decreased 80% within 250 s compared to a 38% decrease for β-lg. Under similar conditions, the κ-casein/β-lg mixture (1:1) showed a faster (2·5 times) decrease in apparent hydrophobicity than κ-casein alone with concomitant exposure of acidic (hydrophilic) groups. The results suggested that the driving force for the rearrangement was mainly hydrophobic, i.e. entropic in origin. The tendency of heated and subsequently cooled κ-casein/β-lg to aggregate reached a maximum after heating at 70 °C for 720 s.

Type
Original articles
Information
Journal of Dairy Research , Volume 55 , Issue 1 , February 1988 , pp. 67 - 80
Copyright
Copyright © Proprietors of Journal of Dairy Research 1988

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References

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