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The influence of milk composition on pH and calcium activity measured in situ during heat treatment of reconstituted skim milk

Published online by Cambridge University Press:  03 March 2010

Jayani Chandrapala ,
Ian McKinnon ,
Mary Ann Augustin  and
Punsandani Udabage
Jayani Chandrapala*
Affiliation:
School of Chemistry, Monash University, VIC 3800, Australia CSIRO Division of Food and Nutritional Sciences, 671 Sneydes Road, WerribeeVIC 3030, Australia
Ian McKinnon
Affiliation:
School of Chemistry, Monash University, VIC 3800, Australia
Mary Ann Augustin
Affiliation:
CSIRO Division of Food and Nutritional Sciences, 671 Sneydes Road, WerribeeVIC 3030, Australia
Punsandani Udabage
Affiliation:
CSIRO Division of Food and Nutritional Sciences, 671 Sneydes Road, WerribeeVIC 3030, Australia
*
*For correspondence; e-mail: jayanic@unimelb.edu.au
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Abstract

The pH and calcium activity of reconstituted skim milk solutions (9–21% w/w milk solids non-fat) on heating and after cooling were studied as a function of milk pH prior to heating (pH 6·2–7·2 at 25°C) and added calcium complexing agents (phosphate or EDTA). The pH decreased as the temperature was raised from 25 to 90°C and the magnitude of the pH decrease was greater with increase in initial pH at 25°C before heating or milk concentration. The pH decrease on heating from 25 to 90°C in skim milk solutions with added calcium complexing agents was lower than that of milk without the addition of these salts. The calcium activity decreased on heating from 25 to 60°C. The magnitude of the change decreased with increase in initial pH at 25°C before heating and milk concentration. The decrease in calcium activity on heating from 25 to 60°C for skim milk solutions with added calcium complexing agents was lower than that of milk solutions without the addition of calcium complexing agents. The changes in pH and calcium activity on heating milk were largely reversible after cooling the milk. The results suggested that the pH and calcium activity at high temperatures are a function of the milk composition. Knowledge of the initial pH prior to heating alone is not sufficient for predicting the changes that occur during heating.

Keywords

pHcalcium activitymilk compositionin situ measurements
Type
Research Article
Information
Journal of Dairy Research , Volume 77 , Issue 3 , August 2010 , pp. 257 - 264
Copyright
Copyright © Proprietors of Journal of Dairy Research 2010

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