.

A B S T R A C T

Looking into the relationship between the air relative humidity (water activity aw) and equilibrium moisture content of food materials is important in maintain good keeping quality and process operations. The adsorption isotherms for tacca starch using different packaging materials (low density polyethylene (LDP), high density polyethylene (HDP)
and plastic) were investigated. Concentrated acid (H2SO4) solutions ranging from 69.50-164.98 ml were used to vary the micro-climate in the study at ambient temperature and aw (0.10-0.80) which is usually experienced in the tropical environment. The experimental data were compared with seven widely recommended models in the literature for food adsorption isotherms (GAB, Oswin, Modified Oswin, BET Hasley, Smith and Henderson). The moisture adsorption isotherms were sigmoidal in shape and was influenced by temperature. The modified Oswin model was found to be most adequate for HDP packaging material while Oswin model was found suitable for plastic and LDP
packaging materials.