MOISTURE-SORPTION ISOTHERMS OF IRISH AND SWEET POTATOES

The sorption properties of dried white varieties of Irish and sweet potatoes were studied at 34C over a range of water activity, 0.10-0.98. A static gravimetric procedure was employed and five sorption models - Bradley; Brunauer, Emmet and Teller (BET); Oswin; Henderson; and Guggenheim, Anderson and de Boer (GAB) - were used in the analysis. For the entire isotherm, both Bradley and Henderson models were suitable for the Irish potato, while Oswin and Bradley models better described the behavior of the sweet potato. Monolayer moisture contents (Mo) for the two potato varieties were calculated using both the BET and GAB equations, and it was found that both crops exhibited the BET type II pattern. The Mo for the two varieties were recommended as the least moisture required for stable storage. Information on moisture sorption regime is required for the storage and the enhancement of stability of stored potatoes both in raw and processed forms. Moisture sorption isotherm is also needed for the prediction and practice of drying, frying and other thermo-related processing of potatoes. It is also required in the determination of critical values for processing such asequilibrium moisture content, critical moisture content and other moisture regimes. It is, in addition, required for the determination of the minimum moisture required for stability of the processed potatoes and therefore necessary information during packaging, and the determination/selection of packaging materials.