Moisture sorption behavior and thermodynamic properties of dry‐crystallized<i>Palada payasam</i>(rice flakes milk pudding) mix determined using the dynamic vapor sorption method
Gajanan P. Deshmukh, Menon Rekha Ravindra, Naveen Jose, Prashant G. Wasnik, Ananta V. Dhotre
Abstract
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 (aw) from 0.10 to 0.90. The MSI were found to closely follow a J-shape curve, conforming to Type-ΙΙΙ 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 aw and decreased with temperature at a constant aw. 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. Practical applications A convenience mix formulation for Palada payasam was developed using dry-crystallization technique, wherein sugar and milk solids are crystallized as a dry coat over cooked ada (rice starch) flakes. The moisture sorption behavior and the thermodynamics of sorption of the dry-crystallized Palada payasam mix analyzed in this study would become as a reference to optimize the final moisture content of this product category and specify its appropriate storage conditions. The sorption data presented will be useful to predict as well as improve the physical, microbiological, and chemical stability of this dry mix during storage. Furthermore, the quantified thermodynamic properties would help in understanding the interaction and binding between the moisture and sorption sites in the product.