Indian Journal of Dairy Science


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Sorption isotherms of infant milk food: Effect of variation of temperature and comparison of various constants in BET and GAB models

D. Prasad and A.K. Agrawal

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