Abstract:
The relationship between air relative humidity (water activity aw) and equilibrium moisture content of food materials is very important in maintaining good quality and process operations. The adsorption isotherm for tacca starch stored in different packaging materials at 20, 30 and 40 °C (low density polyethylene (LDP), high density polyethylene (HDP) and plastic were investigated, with the intent of determining the best storage condition of tacca starch and preserving it for industrial use.
Gravimetric method was used in this study. Concentrated acid (H2SO4) solutions were used to obtain the micro-climate for achieving desired aw in the range of 0.10-0.80, which is usually experienced in the tropical and temperate environment. Twenty grams of tacca starch was measured into each of the packaging materials and kept in the incubator at a preset temperature of 20 0C. Weights were monitored until equilibrium moisture contents were reached. The same procedure was followed for 30 and 40 0C, respectively. The proximate composition and functional properties of equilibrated samples were determined.
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 showed a great influence on 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 at 30 °C. GAB model produced best fit for all the packaging materials at 20 and 40 °C. In other to have prolonged shelf-life and good storage condition for tacca starch, plastic packaging material could be best used. The physico-chemical properties of tacca starch was found better than some commercial starches such as potato starch, corn starch which is a potential for food applications.
