Moisture sorption isotherm characteristics of plantain (Musa, AAB)

Moisture sorption isotherms of fresh, pre-treated and freeze-dried plantain , at 40 degrees C, 50 degrees C and 60 degrees C, were constructed using th e static gravimetric method. The pre-treatment involved blanching and infus ion in 40 degrees Brix sucrose at 4 degrees C for 16 h. The isotherms of th e fresh plantain were of BET type II, while those of the freeze-dried sampl es were BET type I. Hysteresis was observed between the adsorption isotherm of the freeze-dried plantain and the desorption isotherm of the fresh samp les. At low values of a(w), below 0.40, the moisture contents of the pre-tr eated samples were lower than that of the fresh plantain, at corresponding values of a(w). However, above a(w) 0.50 the reverse applied. In both desor ption and adsorption an increase in temperature resulted in lower equilibri um moisture contents at corresponding values of a(w). The monolayer moistur e contents of the moist-infused and freeze-dried samples were lower than th ose of the fresh material. Of the five models tested the Henderson, S. M. ( 1952, Agricultural Engineering 33, 29-33) and GAB (1981) versions fitted be st to the isotherms of the fresh material. The Iglesias & Chirife model (19 78) was the best fit to the isotherm of the infused material. The isosteric heat of sorption for the fresh plantain, ranged from 47.4 kJ/g mol at 18% moisture, dry solids basis, to 73.2 kJ/g mol at 2% moisture, dry solids bas is. The comparable range for the freeze-dried material was 42.2-635 kJ/g. m el. (C) 2000 Elsevier Science Ltd. All rights reserved.