Effects of Drying Methods on the Quality of Dried Kiwifruit

In this study, 'Xuxiang' kiwifruit was used as the research object, and vacuum drying, hot air drying and freeze drying were used to process kiwifruit. The effects of several drying methods on the color, texture, nutritional quality and volatile compounds of kiwifruit were studied to determine the appropriate drying methods for kiwifruit, which would provide theoretical support for the deep processing of kiwifruit. The results showed that the freeze-dried kiwifruit could maintain the original color to the maximum extent, and it's a^* value was −7.24, which was closest to the fresh sample. The firmness, toughness and chewiness of freeze-dried kiwifruit were significantly lower than the other two groups (P<0.05). The V_C content of kiwifruit produced by freeze drying was 278.56 mg/100 g, total phenol content was 1.35 mg/g, which were significantly higher than those produced by vacuum drying and hot air drying. Therefore, freeze-drying treatment could significantly reduce the loss of nutrients in kiwifruit. As for volatile components, 46 volatile components were detected in fresh samples, and the main volatile components were (E)-2-hexenal and methyl butyrate. Fifty-three volatile components were detected in hot air dried kiwifruit, the main volatile components were ethyl caproate and ethyl octanoate. Forty-eight volatile components were detected in vacuum dried kiwifruit, and the relative contents of furfural and 6-methyl-5-heptene-2-one were higher. Forty volatile components were detected in freeze-dried kiwifruit, and the content of ethyl butyrate was the highest. However, some negative odors such as 4-methyl-3-penten-2-one, butyric acid and hexanoic acid were produced after hot air drying and vacuum drying. The kiwifruit produced by freeze drying method contains more volatile substances in fresh samples, and (E)-2-hexenal and methyl butyrate were detected only in freeze drying group. In general, freeze-drying can maintain the flavor of fresh kiwifruit.