Moisture sorption characteristics of heat desiccated milk sweet 'Khoa-peda' prepared from buffalo milk

Water activity (a(w)) is a valuable criterion in food processing affecting food product design and in ensuring food safety during storage. Khoa-peda is an indigenous khoa based dairy sweet prepared by mixing khoa and sugar and is popular all over India. It has a maximum shelf life of 15 days at refrigerated temperatures. The moisture sorption parameters of Khoa-peda prepared from buffalo milk were determined at three different temperatures 15, 25 and 35 degrees C using a gravimetric-static method. The moisture sorption isotherms were found to be of sigmoid shape reflecting a Type II isotherm. At all water activities, the equilibrium moisture content was lower at higher temperatures. From amongst the GAB, Modified Mizrahi, Oswin, Caurie and Halsey models applied to the experimental sorption data of khoa-peda, the GAB model best described the sorption isotherm throughout the entire range of a w. Temperature dependence of GAB parameters was determined by using Arrhenius type equation to correlate the GAB constants with temperature. The hysteresis effect was observed at all the temperatures over the entire range of water activities. The hysteresis loop was of Type `C' according to Everett classification. The effect of temperature was found to reduce the hysteresis. The hysteresis amplitude reduced from 0.303 at 15 degrees C to 0.253 at 35 degrees C, total hysteresis units decreased from 1.55 units at 15 degrees C to 1.25 units at 35 degrees C and the hysteresis energy reduced from 67.72 kJ/kg of water at 15 degrees C to 32.25 kJ/kg of water at 35 degrees C.