An evaluation of different pretreatment methods of hot-air drying of garlic: Drying characteristics, energy consumption and quality properties

Various drying pretreatment techniques play an important role in the drying process. This study investigated the effect of ultrasound (US), osmosis (OM) and freeze-thaw (FT) pretreatments on the hot-air drying characteristics, physical characteristics, rehydration characteristics, and allicin content of garlic. The results showed that the application of different pretreatments increased the drying efficiency and reduced the total energy consumption, compared with unpretreated garlic. Particularly, drying garlic with US pretreatment reduced the drying time by 450, 270 and 90 min and the total energy consumption was 24.45%, 20.60% and 18.09% less at 50, 60 and 70 °C, respectively. These improvements attribute to an increasement in porous structure by US, which leads to an increase in water diffusion capacity. Moreover, US drying had lowest color difference, highest rehydration rate and allicin content. The Midilli model could satisfactorily describe the drying curves of US pretreated garlic.