Optimization of Drying Conditions of Kiwi Rings with Osmo-solar Dehydration

It is the oldest and most common traditional food preservation method known to dry by laying food products under the sun. However, if the food product is in direct contact with the sun light, there is a decrease in the color and nutrient values of the product. To solve these problems, solar dryers have been developed which can be utilized due to indirectly the effect of the sun. In this study, kiwi rings were dried by using osmosolar dehydration as a combination of osmotic dehydration and solar drying. Kiwi rings were first immersed in sucrose solutions and then dried in a solar dryer. Response Surface Methodology used to determine effects of the conditions ondrying performance and find out optimum levels drying conditions for the responses to a safe level. In the response surface method, the drying conditions were selected as the kiwi slice thickness (A), sucrose concentrations (B), immersed time (C) and solar drying time (D). The response to be optimized was chosen as water loss, diameter shrinkage ratio and greenness (a) color change. A successful mathematical model was obtained by the response surface method between the drying conditions and the responses. The suitable model is chosen quadratic for water loss, 2FI model for color change model and shrinkage ratio. The model R2 value is 0.952 for water loss, 0.737 for a color change and 0.856 for shrinkage ratio. The regression coefficients, along with the corresponding P-values, for the model of production water loss, a color change and shrinkage ratio are described by ANOVA. Values of "Prob>F" less than 0.0500 indicate model terms are significant. In this case B, C, C2 are significant model terms for water loss. A, B, C, AB, AC, AD, BC and CD are significant model terms for color change and B, C, AC, AD, BD, CD are significant model terms for shrinkage ratio. The optimum drying conditions levels was determined to sucrose concentration 12.7 %w/v, ring slice thickness 4.06 mm, solar drying time 125 min and immersed time 70.9 min, respectively. In addition, pretreatment of osmotic dehydration was found to be effective in drying kiwi rings with solar tray dryer.