Sorption Isotherms of Infant Milk Food — Effect of Variation of Temperature and Comparison of Various Constants in BET and GAB Models*

Abstract

Human milk is universally regarded ideal for the feeding of infants. Yet, owing to variouscauses, an infant may not derive adequate nutrition from the mother and it may becomenecessary to feed the infant either wholly or partly with milk from other sources such as infantmilk food. Water activity is an important concept in the food industry since it is related tomicrobiological stability and physico-chemical deteriorative reactions. The present investigationwas carried out with specific objective to determine water activity (aw) of infant milk food atdifferent temperatures and also to evaluate and compare BET and GAB models with dataobserved during investigation. Gravimetric method was used to determine the equilibrium moisturecontent (EMC) of infant milk food at different temperatures (30, 40 and 50°C) by keeping thesamples in a range of atmospheres of relative humidity from 11.1 to 92.3%. The EMC's ofintermediate milk food was found to vary from 0.0185 to 0.4432 (db). The data recorded couldbe fitted to GAB model satisfactorily for the entire range of water activity with acceptablevalues of coefficient of determination in the range of 0.962 to 0.984. The BET model provided agood description of the isotherms of infant milk food only in the range of water activity < 0.45.