Sweet potato (Ipomoea batatas Lam.) dehydration by osmotic concentration and tray drying

The feasibility of osmotic concentration and subsequent air drying of osmotically concentrated sweet potato was demonstrated. Diced sweet potatoes were contacted with 50%, 60%, and 70% (w/w) sucrose-water solutions at three temperatures (20, 30, 40°C) . The moisture loss and solute uptake during osmotic contacting were monitored and modeled using an exponential equation. The parameters of the equation for moisture loss and solute uptake were estimated using non linear regression.

Osmotically concentrated (OC) diced sweet potato was air-dried in a tray dryer. The air drying characteristic of (OC) sweet potato was compared with that of the fresh sweet potato. Fresh sweet potato exhibited two falling-rate drying periods with no constant rate drying. The air drying rates of diced sweet potato which was osmotically concentrated for two h (0C2H) were similar to that of the dices concentrated for five h (0C5H) in the osmotic solution of the same concentration and temperature (70%, 25°C). Drying rate equations were developed by expressing the drying rates as linear functions of the moisture content on a dry basis. The parameters of the exponential equation for osmotic concentration and linear equations for air-drying were estimated with r² values no less than 0.93. These equations provide useful information for the design of sweet potato dehydration processes.