Effect of trehalose and ultrasound-assisted osmotic dehydration on the state of water and glass transition temperature of broccoli (Brassica oleracea L. var. botrytis L.)

The effects of trehalose and ultrasound-assisted osmotic dehydration on the glass transition temperature (Tg′) and the state of water in broccoli were analyzed by using differential scanning calorimetry (DSC), low field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI). The results showed that osmotic dehydration using trehalose can affect the Tg′ of broccoli by changing the state of water within the sample structure. The values of Tg′ of the osmotically dehydrated broccoli samples ranged between −27.52 °C and −23.31 °C, which constituted an increase of about 2-6 °C compared with that of the untreated sample. Compared with the normal osmotic dehydration with 2 h, ultrasound-assisted dehydration with shorter time (30 min) could get the higher value of Tg′ by increased the water loss and accumulation of trehalose and decrease the mobility of water in the broccoli cell tissue. However, when the ultrasound treatment time was 40 min, it resulted into decrease in Tg′ indicating the important role of treatment time in ultrasound-assisted osmotic dehydration process.