COMPARISON OF A NOVEL VACUUM-COMBINED INFRARED AND HOT-AIR CONVECTION METHODS FOR DRYING OF DEVECI (PYRUS COMMUNIS L.) PEAR SLICES

Abstract

In this study, the quality characteristics of pear slices dried in vacuum-combined infrared dryer equipped with a two-way infrared heating (100-300 W infrared power) and convectional dryer (40-70 °C) were comparatively investigated. Increasing infrared power in vacuum-combined infrared dryer decreased the drying time.  However, the differences between vacuum pressures (100 mmHg and 250 mmHg) were generally negligible. Drying process at 200 and 300 W IP under vacuum was approximately 2- and 2.5-times shorter than conventionally drying at 55 and 70 °C, respectively. Although a very low amount of HMF in dried pear slices by the conventional dryer was detected only at 70 °C after 300 min, high amounts of HMF was detected at 300 W after 120 minutes. The rehydration rate of pear slice dried with vacuum-combined infrared dryer was higher than those of pear slice dried with conventional dryer. Syringic, chlorogenic and ellagic acids were identified in dried pear samples. Chlorogenic acid was found to be the most among phenolic compounds in dried pears. While the ellagic acid was not detected in fresh pear, dried pears had ellagic acid content (8.14-16.93 mg/kg d.m.). It was found that total phenolic content, ABTS and DPPH values of dried pears by vacuum-combined infrared dryer was lower than those of dried sample by conventional dryer. The pear slices dried at 300W and 250 mmHg had the highest sensory scores. The results show that the vacuum-combined infrared drying provided a shorter drying time and better sensory quality for dried pear compared to conventional drying.