A Akbari, M Shahedi, N Hmadami, Sh Dokhani, M Sadeghi,
Volume 13, Issue 47 (4-2009)
Abstract
Sun drying is a well-known food preservation technique that reduces the moisture contents of agricultural products. Shrinkage, rehydration ability and color of food materials during air drying adversely affect the quality of the dried products. Since all fresh tomatoes can not be consumed at the time of harvest, preservation provides a larger market, allowing consumers to buy the preserved tomato through the year. A natural convection solar dryer consisting of a solar air heater and a drying chamber was manufactured in this research. Tomato slices were dried in the solar dryer and compared with open sun drying. Also, tomato slices were dried in a laboratory oven (operated at temperature 50, 60, 70, 80°C). With increasing the temperature, the time required to arrive certain moisture content is decreased. Also results showed that drying time in the solar dryer is shorter than open sun drying. In other words, drying time was reduced 17 to 45% by the solar drying in comparison to open – sun drying. The experimental shrinkage data showed a linear behavior with moisture content. Also, the experimental data didn't show a strong effect of temperature on the rehydration ability of the product. Thus, the effect of temperature and method of sun drying on the shrinkage phenomenon and the rehydration ability can be neglected. Tomato slices dried at 50°C had better appearance (lightness and red color) than at 80°C.
