14A-5

D. UZMAN, Food Engineering, Hacettepe University, Beytepe Campus, Ankara, 06532, Turkey and F. Sahbaz.

Osmotic dehydration is a novel technique used to dehydrate foods. This technique has been used as a preprocessing step before drying, freezing, and pasteurization, to improve quality of the products and to save energy. In osmotic dehydration, food products (generally fruits and vegetables) are soaked in concentrated aqueous solutions, usually of sugar or salt. During this process, water flows out from the product to the solution, and solute in the concentrated sugar/salt solution diffuses into the product. The two main mass transfers continue until the water activity (a_w) of the apples and the osmoactive solution are equal. However, the equilibrium conditions should be determined to evaluate the effectiveness of a dehydration process.

Our objective was to determine the equilibrium conditions attained during osmotic dehydration of apples in glucose solutions at three different concentrations and temperatures.

Osmotic dehydration of apples (Golden Delicious) was carried out in 40%, 50% and 60% (w/w) glucose solutions at temperatures of 30, 40, and 50 °C. Weight reduction (WR), water loss (WL), glucose gain (GG), a_w, soluble solute concentration (SSC), and soluble solute gain (SSG) of apples and a_w and SSC of osmotic solutions were determined at different time periods (10, 30, 60, 90, 150, 300, 1020, and 1440 min). Enzymatic method has been used to determine the glucose content of apples.

Our results showed that at the end of 1440 min, an equality of a_w was achieved. A two-parameter kinetic model was used to evaluate the experimental data. The comparison of the experimental data for WR, WL, GG, SSG with the equilibrium values obtained from the kinetic model also showed that the equilibrium was attained during the given time period.