Abstract: The effects of microwave vacuum freeze drying (MVFD), microwave vacuum puffing (MVP), short- and medium-wave infrared drying (ID) and vacuum freeze drying (VFD) on the eating and nutritional qualities of Chinese jujube were determined. The results showed that the contents of total sugar and reducing sugar increased after drying. The total acid content declined after all drying treatments except short- and medium-wave ID. No significant changes in the color and browning degree occurred after MVFD and MVP. MVFD resulted in the highest retention rate of VC (98.62%), whereas jujube fruits dried by short- and medium-wave ID showed the lowest VC contents. The total phenolic content in jujubes after MVP and MVFD significantly increased to 4 721.30 and 4 516.25 mg/100 g md, respectively. The total flavonoid content after VFD was significantly higher than that in samples dried by other drying methods (P < 0.05). The eating and nutritional qualities of Chinese jujube after ID were more seriously damaged. Microscopic observation demonstrated that VFD fruits had a highly porous honeycomb structure. In addition, MVFD fruits displayed large and uniform pores, while the structure of MVP fruits was more loose, showing a large number of small granules. ID fruits exhibited a dense structure without cavities. In summary, dried jujube obtained after MVFD and MVP had better eating and nutritional qualities in terms of color, aroma, taste and appearance, which were similar to those of VFD samples. Due to their low cost and high efficiency, both MVFD and MVP are significantly advantageous for producing high quality jujube products in the future with broad application prospects.

Key words: microwave vacuum freeze drying, microwave vacuum puffing, short-and medium-wave infrared drying, vacuum freeze drying, nutritional qualities