Effect of combined radio-frequency and solar assisted air drying on properties of dried apricot

Dried apricot, one of the most important agricultural export commodities of Turkey, is still produced by using traditional drying (sun drying) method with the expense of high product losses and low grade products with lower economical value. In this study, the experimental design was generated using response surface methodology for radio-frequency drying experiments following solar assisted air pre-drying. For this purpose, the effect of independent variables on the response values was investigated with Box Behnken experimental design for drying of unsulfured apricots. Independent variables were pre-drying temperature (50-70°C), pre-drying time (300-1140 min), radio-frequency electrode gap (77-85 mm) and radio-frequency drying time (270-690 min). Moisture content (%), quantity of browning products (A420/gdryweight), total color change (ΔE) and hardness value (N) were selected as the responses. The drying conditions were optimized for minimum process time, browning, color change and optimum hardness and moisture content. Under optimum conditions of 63.5 °C pre-drying temperature, 895 min pre-drying time, 77 mm distance between radio-frequency electrodes and 385 min radio-frequency drying time; the moisture content (%), quantity of browning products (A420/gdryweight), total color change (ΔE) and hardness (N) were 22.31±2.82, 0.69±0.03, 37.65±2.23 and 1293.46±61.96, respectively. Radio-frequency drying following solar assisted air drying system provided high quality whole apricots while reducing the processing time.