Abstract:

The microwave-assisted vacuum freeze-drying of Dioscorea opposite was executed to obtain high-quality dried
products. Drying characteristics and quality traits of dried Dioscorea opposita were investigated. The effects of three drying
conditions including sample slice thickness, vacuum degree in drying chamber and microwave power on the rehydration
ration, polysaccharide yield and L value (brightness) of dried products were examined. Linear weighting method was used
to analyze comprehensive multi-objective optimization to determine the optimal values of the studied parameters. The
results showed that the influences of these three factors on the overall index score were in the decreasing order of slice
thickness > vacuum degree > microwave power. The optimal drying conditions were slice thickness of 5 mm, degree of
vacuum of 100 Pa, and microwave power of 3.75 W. The drying time to achieve safe moisture content of 0.12 g/g (dry
basis) was 150 min and drying energy consumption was 7 875.9 kJ/kg. Under these conditions, the quality of the dried
product was excellent with good rehydration ratio (95.6%), pure color (the value of color difference was 92.90) and
high polysaccharide yield (18.97%).

Key words: Dioscorea opposita, microwave, vacuum freeze-drying, quality