Journal of Dairy Research



Effect of Minerals on Casein Micelle Stability of Cows' Milk


Alexandros Tsioulpas a1, Michael J Lewis a1c1 and Alistair S Grandison a1
a1 School of Food Biosciences, The University of Reading, Whiteknights, PO Box 226, RG6 6AP, Reading, UK

Article author query
tsioulpas a   [PubMed][Google Scholar] 
lewis mj   [PubMed][Google Scholar] 
grandison as   [PubMed][Google Scholar] 

Abstract

The effects of minerals on casein micelle stability of individual cows' milk, throughout a complete lactation, were investigated. Calcium and calcium ions, magnesium, phosphorus, sodium, potassium and citrate contents were analysed, together with the following physical properties of milk; pH, ethanol stability, rennet clotting time and coagulum firmness. There was an inverse non-linear relationship between free calcium ion concentration and ethanol stability (ES; r=0·84). Rennet coagulation time showed a weaker relationship with free calcium ion concentration (r=0·44) but a stronger relationship with pH (r=0·66). In addition, samples containing higher amounts of free calcium ions produced a firmer gel. Citrate in natural samples acts as a stabilizing factor, as it slightly improves milk stability. Potassium, on the other hand, exhibited a negative correlation, but only with rennet clotting time (r=−0·52). Throughout lactation the average values were; free Ca2+ concentration 1·88 mM, pH 6·63, ES 83·2% and clotting time 13·6 min. The equilibrium relationship between pH and free Ca2+ concentration was investigated by adjusting milk pH from 5·9 to 7·1, using acid and alkali. There was a good inverse linear relationship between pH and log (free Ca2+) for individual milk samples, with a gradient of −0·62 and a standard deviation of 0·042.

(Received August 31 2005)
(Accepted September 6 2006)
(Published Online February 12 2007)


Key Words: ionic calcium; casein micelle stability; ethanol stability; mineral composition.

Correspondence:
c1 e-mail: m.j.lewis@reading.ac.uk