Monolayer moisture, free energy change and fractionation of bound water of red chillies

Abstract The equilibrium moisture content and water activity data of red chillies within the temperature range 25–45 °C were used to determine the monolayer moisture, free energy change and fractionation of bound water. The BET equation, Caurie equation and local isotherms fixed the safe storage moisture limits of red chillies as 3.84–6.68%, 5.2–6.01% and 6.03–7.69% d.b. in adsorption conditions and 5.85–9.17%, 5.66–6.77% and 6.02–9.76% d.b. in desorption conditions within a temperature range of 45–25 °C, respectively. The free energy was higher in the desorption process than in the adsorption process of chillies at all the temperatures and moisture contents. The maximum value of free energy was 4437.35 kJ/kg mol at 5% d.b. moisture content and the minimum value was 238.37 kJ/kg mol at 50% d.b. moisture content during desorption of chillies in the temperature range of 25–45 °C. It was observed that the primary, secondary and tertiary bound waters end at moisture contents of 1.5%, 14% and 53.6% d.b., respectively. The bound water in red chillies was limited up to a moisture content of 53.6% d.b. and beyond that was free water, which can be removed easily.