Study of sorption isotherm and isosteric heat of Kepok Banana (Musa paradisiaca F.) slice

Kepok banana (Musa paradisiaca F.) is an abundant commodity in Indonesia. This commodity is a kind of horticulture that has high risk to be defect and damage, moreover if it is handled with poor of post-harvest technology, it makes the economic value of this commodity comes low. The processing is needed in order to preserve quality and to improve economic value. Kepok banana contains high amylose and starch around 29.50% so it is suitable to be processed as flour. The critical step of flour processing occurs in the drying process of banana slices so this research focused on slices form. Two important factors of drying process are the equilibrium water content and water activity (a_w). The relationship between moisture content and a_w at constant temperature is known as Moisture Sorption Isotherm (MSI). The MSI of Kepok banana slice was experimented by static gravimetric method with 5 types of saturated salt in a_w range of 0.05-0.90 at 30°C, 40°C, and 50°C. It was tested by BET (Braunauer, Emmet and Teller), Smith, Oswin, Caurie, and GAB (Guggenheim-Anderson-de Boer) model. Then the isosteric heat was calculated using the Clausius-Clapeyron equation. The results showed that the equilibrium moisture content at constant temperature increases with increasing of a_w value, while at constant a_w equilibrium moisture content decreases with increasing temperature. The most appropriate model in describing the characteristics of MSI Kepok banana slices is GAB model and is classified in type II. In addition, the isostreric heat for desorption is higher than adsorption.