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Reversibility of shrinkage of mineral acid casein curd as a function of ionic strength, pH and temperature

Published online by Cambridge University Press:  01 June 2009

Cheng Tet Teo ,
Peter A. Munro  and
Harjinder Singh
Cheng Tet Teo
Affiliation:
Department of Food Technology, Massey University, Palmerston North, New Zealand
Peter A. Munro
Affiliation:
Department of Food Technology, Massey University, Palmerston North, New Zealand
Harjinder Singh
Affiliation:
Department of Food Technology, Massey University, Palmerston North, New Zealand
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Summary

Mineral acid casein (MAC) curd was subjected to a range of ionic strength, pH and temperature conditions to explore their effects on curd water-holding capacity, particularly the reversibility of shrinkage. The shrinkage of MAC curd on whey removal during the washing stage of casein manufacture could be attributed almost completely to the reduction in ionic strength and not specifically to either calcium or lactose removal. This shrinkage on whey removal during washing could not be reversed by adding whey back to the curd to attain the original ionic environment. In this sense it was irreversible. The pH during formation of MAC curd was more important than later pH adjustments in controlling curd water-holding capacity. The effect of a high precipitation pH in creating a tough, compact curd could not be reversed by subsequently decreasing the pH. However, the effect of a low precipitation pH in creating a soft, open curd could be partly reversed by subsequently increasing the pH. MAC curd shrank by 45% when the temperature was increased from 20 to 80°C. This temperature-dependent shrinkage was virtually fully reversible on cooling. It is suggested that the water-holding capacity of casein curd is governed largely by hydrophobic interactions and that once such interactions have occurred they cannot easily be disrupted by small changes in either pH or ionic strength.

Type
Original Articles
Information
Journal of Dairy Research , Volume 63 , Issue 4 , November 1996 , pp. 555 - 563
Copyright
Copyright © Proprietors of Journal of Dairy Research 1996

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References

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