Vol. 11, Issue 3 (2022)

Author(s):
Minati Mohapatra and Ashok Kumar

Abstract:
Salt and heat treatment to parboiled rice (pre-conditioning) to bring low moisture level (10% wb) is a pre-requisite for its puffing. Rapid moisture adsorption deteriorates puffing quality, and knowledge on Moisture Sorption Isotherm (MSI) characteristics becomes essential for appropriate packaging design. MSI of raw, parboiled and pre-conditioned rice with different salt levels (0.0, 2.5, 3.5 and 5.0% w/w) were determined at 20, 30, 40 and 50ºC following isopiestic vapor transfer method. Equilibrium moisture content (EMC) of pre-conditioned rice were lower than raw and parboiled rice, but followed a crossover phenomenon beyond water activity range of 0.55 – 0.75. All exhibited type II BET isotherms. Modified GAB model is best fit model tested. Microstructure of pre-conditioned rice revealed continuous and compact surface that influences sorption. The net isosteric heat of sorption showed exponential relation with moisture content from 5.0- 30.0% db and lower for salt conditioned rice than control samples.