Abstract
In the semi arid conditions of Sudan, the determination of moisture sorption isotherms at different temperatures and water activities to establish the correctly storage conditions for crops grains is highly needed. The objective of this study was to determine the moisture sorption isotherms of two local varieties of sorghum (Sorghum bicolor L Moench.) namely; Tabat and Wad Ahmed at various temperatures and water activities. The study was conducted at the Department of Agricultural Engineering, University of Khartoum and the Department of Grains Technology, Food Research and Processing Center, Shambat, Sudan during the period from December 2006 to December 2008. Water sorption isotherms were determined using standard static gravimetric method at temperatures 25oC; 35oC and 45oC over a range of water activities from 0.112 to 0.865. The water activities were maintained using saturated salt solutions inside air-tight glass desiccators, while incubators were used to maintain a constant temperature. The results showed that, there is a highly significant (P ≤ 0.01) effect of water activity nested within temperature and also for the interaction between water activity nested within temperature and cultivars. Wad Ahmed cultivar gave the highest values of adsorption (13.633%db) and desorption (15.665%db) equilibrium as compared to Tabat cultivar (13.615%db and 15.410%db, respectively) at the same temperature and water activities. Increasing temperature from 25oC to 45oC decreased the sorption isotherms at a constant water activity, while increasing water activities from 0.112 to 0.865 increased the sorption isotherms for both adsorption and desorption equilibrium at a constant temperature. It is concluded that, moisture sorption isotherms of sorghum grains play important roles in such technological processes as drying, handling, packaging, storage, mixing and other processes that requires the prediction of food stability, glass transition and estimation of drying time and texture and prevention of deteriorative reactions.
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