Moisture sorption behavior and thermodynamic properties of dry-crystallized Palada payasam (rice flakes milk pudding) mix determined using the dynamic vapor sorption method

摘要

The moisture sorption isotherms (MSI) of a dry-crystallized Palada payasam mix and its thermodynamic properties were investigated using the dynamic vapor sorption (DVS) method at 20, 30, and 40°C over a range of water activity (a_w) from 0.10 to 0.90. The MSI were found to closely follow a J-shape curve, conforming to Type-Ⅲ of Brunauer–Deming–Deming–Teller classification. The Guggenheim–Anderson–de Boer (GAB), Peleg, Iglesias, and Chirife models best described the sorption behavior of Palada payasam mix with a good fit to the sorption data at all three temperatures. The analysis for sorbed water based on the Caurie's model revealed an inverse trend with temperature for the number of adsorbed sites, percent bound water, and surface area while the density increased with temperature. The isosteric heat of sorption computed using the Clausius–Clapeyron equation for the dry mix was found to exponentially decrease from 55.23 to 44.29 kJ mol~(-1) with increase in moisture content from 1% to 40%. The spreading pressure increased with a_w and decreased with temperature at a constant a_w. The domination of enthalpy-driven process in the sorption of the mix was established using the compensation theory. The X-ray diffractogram of the product confirmed a crystalline fraction of 65% in the mix.