Convective and microwave drying characteristics of sorbus fruits (sorbus domestica l.)

Abstract

In this research, convective and microwave drying characteristics, energy requirement and color changes of sorbus fruits (Sorbus domestica L.) were reported. Sorbus fruits were dehydrated in a computer connected parallel air flow type dryer and in a microwave oven dryer. Samples of freshly harvested sorbus fruits were dehydrated under two air temperatures of 50 degrees and 70 degrees C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for both temperatures. Sorbus fruits were dehydrated from the initial moisture content of 300 (percentage dry basis) to a final moisture content of 8 ... 10%. During convective drying experiments, product were weighted automatically by the balance per 5 ... 10 minutes. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per 15 ... 60 minutes. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (Delta E) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for sorbus fruits. The minimum specific energy requirement were determined as 0.69 kWh/kg and 37.07 kWh/kg for 70 degrees C and PL-3 respectively. 50 degrees C drying air temperature and PL-1 was found to yield better quality product in terms of color retention of Hunter L, a, b and Delta E. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.