Abstract
•The ultrasound and vacuum enhanced the mass transfer during OD of garlic slices.•A novel OD method for garlic slices was proposed – VUOD.•VUOD markedly enhanced the mass transfer compared to NOD, VOD and UOD method.•The mass transfer mechanism of VUOD was proposed.•The quality of dehydrated garlic slices was improved by VUOD.
This study investigated the effects of multi-frequency mode ultrasound and vacuum technology on the water loss (WL) of garlic slices during osmotic dehydration (OD), and their effects on the microstructure of garlic. A new method of OD for garlic slices was proposed – Vacuum pretreatment coupled to ultrasound assisted osmotic dehydration (VUOD). The results indicated that the WL of the garlic slices treated with VUOD (21.12%) was significantly (p < 0.05) higher than slices treated with normally OD (NOD) (10.67%), vacuum pretreatment OD (VOD) (14.18%), and multi-frequency mode ultrasound assisted OD (UOD) (11.20–13.56%). A mass transfer mechanism of VUOD was proposed. Low-field nuclear magnetic resonance results quantified the moisture migration in the vacuole, cytoplasm and intercellular space, and the cell wall of garlic cells. The quality properties (allicin content, surface color change and firmness) of VUOD treated garlic slices are predominately better than NOD, VOD and UOD treated samples.