Moisture sorption isotherms of modified cassava flour during drying and storage

Modified cassava flour is produced by drying processes and usually, in Indonesia, stored for several months after production up to selling and utilization. During storage, flour can experience degradations in quality, particularly if ambient conditions are unfavorable. In the present study, the adsorption and desorption isotherms of modified cassava flour were determined over a range of water activities (a_w) from 0.05 to 0.84 at three different temperatures (27, 40 and 50°C), which are commonly experienced in the tropical environment, using the static gravimetric method. The suitability of eight widely recommended mathematical models in the literature for food sorption isotherms were investigated. The modified cassava flour shows a type II (sigmoid) isotherm curve and the moisture sorption hysteresis loop was observed at all examined temperatures. The effect of the temperature on both adsorption and desorption isotherms for the complete range of water activity (a_w) was observed. Adsorption and desorption data of modified cassava flour were best fitted by the Henderson, Peleg, and Chung-Pfost models at 27, 40 and 50°C, respectively. According to the adsorption results, the moisture content of modified cassava flour should not be higher than 9.34% (db) at room temperature (27°C) to ensure microbial stability during storage.