Application of response surface methodology for optimization study of equilibrium moisture sorption content for efficient drying and storage of pearl millet flour

Pearl millet due to its high nutritional quality and adaptability to adverse cultivation is highly consumed in Asia and Africa. Prevalent flour form of pearl millet is susceptible to oxidation and microbial growth, demanding proper drying and storage conditions. Moisture sorption isotherm plays an essential role for proper storage and drying operation optimization. This study used response surface methodology to optimize equilibrium moisture content (EMC) of adsorption and desorption (closely related to moisture sorption isotherm) as response and the independent variables affecting the response were sorption temperature, water activity of sorption of flour and time of pre-treatment of grains before grinding them to flour. Linear relationship was found for water activity and time of pre-treatment with the response but an inverse relation was noted between the sorption temperature and the response. The optimized conditions obtained for minimized response of adsorption EMC were 19.85 °C temperature, 1.34 h of pre-treatment time and 0.41 sorption water activity which gave optimized EMC of 9.0554 g/100 g dry basis. Optimization condition for minimized desorption EMC were 24.47 °C temperature of sorption for 0.13 h pre-treated pearl millet grain flour and 0.360 sorption water activity providing an optimized EMC of 11.07 g/100 g dry basis. Isosteric sorption heat was also calculated and was found to be in range 22.03–0.736 kJ/mol for adsorption and 33.03–1.067 kJ/mol for desorption. Present work was an effort to evaluate optimized conditions to develop effective storage and drying processes to preserve pearl millet flour thereby increasing its shelf life.