Effects of Three Drying Methods on Drying Quality of Mu-jujube at Different Harvest Periods

In order to make full use of jujube resources and further explore the processing and utilization value of jujube fruit, the changes of jujube nutrition, color and quality indexes after natural drying, hot air drying and vacuum freeze-drying in different harvesting stages were compared and analyzed using mu-jujube fruit as the test material. The results showed that the contents of V_C, crude fiber, flavonoids and triterpenoids of white ripe dates were higher than those of semi-red dates, and those of semi-red dates were higher than those of all-red dates under the same drying methods. The contents of soluble sugars and polysaccharides of white ripe dates were significantly (P<0.05) lower than those of semi-red dates and the semi-red dates were significantly (P<0.05) lower than those all-red dates. Except for soluble sugars, all three harvesting stages of jujube had the highest content of functional nutrients after vacuum freeze-drying, but the content of crude fiber, flavonoids and triterpenoids after natural drying or hot air drying were higher at the white ripening stage and the semi-red stage than that of all-red stage of jujube fruit after vacuum freeze-drying. Flesh color of jujube during three harvest stages were green and white. The jujube texture at white ripe period was relatively hard, there was no significant difference between half red period and full red period (P>0.05). The original color, quality and texture of jujube were kept by vacuum freeze drying, while the flesh of white ripe period and half red stage jujube turned green to red, and the color difference and hardness increased after natural drying and hot air drying, which were close to or even higher than that of full red stage jujube. It could be concluded that the early harvested white and semi-red jujube fruit had better processing characteristics, and vacuum freeze-drying was the best drying method for high-value drying process. The results would provide a theoretical basis for early harvesting and processing of jujube fruit.