不同前处理和冻结方式对苹果片真空冷冻干燥效率及干制品品质的影响

冻干前处理和冷却固化环节是果蔬冻干的关键工序，为进一步缩短干燥时间并提高干制品品质，该研究选用苹果片作为试验对象，采用超声波技术、真空冻结技术、超声波-真空冻结技术，将苹果片分为常规组、超声-常规组、真空冻结组、超声-真空冻结组，比较不同前处理方式对苹果片冻干效率及干制品品质的影响。结果表明，超声-常规组苹果片冻干效率最高，由16.00 h缩短至11.83 h；干制品复水比最大，较常规组增加了62.16%；色泽指标b*值由28.24降至19.46，颜色更加洁白；维生素C保留率最高，可达83.90%；硬度最小且松脆可口，感官评价最好。真空冻结组苹果片冻干时间由16.00 h缩短至14.17 h；干制品复水比较常规组增加了17.99%；色泽指标b*值由28.24降至22.98，颜色较为洁白；酥脆性良好且有较好的咀嚼感，感官评价良好。研究结果为苹果片在冻干前处理环节参数优化及新型果蔬脆片的开发提供参考。
Pre-treatment, cooling, and solidification are key processes in the freeze-drying of fruits and vegetables. In order to improve the efficiency of vacuum freeze-drying and ensure the quality of freeze-dried products, apple slices were subjected to different pre-processing and freezing methods including ultrasonication, vacuum freezing, and ultrasound-vacuum freezing. The apple slices were randomly divided into 4 groups: conventional group, ultrasound-conventional group, vacuum-freezing group, and ultrasound-vacuum-freezing group. The drying times and quality indicators for these groups were compared. The results showed that the ultrasound-conventional group, which was subjected to ultrasound followed by vacuum freezing in the refrigerator, showed the best drying efficiency. The drying time reduced from about 16.00 h to 11.83 h. The rehydration rate of dried apple slices was also the highest in this group, which increased by about 62.16% compared to the conventional group. The b* value of dried apple slices reduced from 28.24 to 19.46, and the color was whiter. The retention rate of vitamin C was also the highest, reaching 83.90%. The hardness was the lowest, giving crisp apple slices, and the sensory evaluation gave the best results. The vacuum-freezing group, which was subjected to vacuum freezing during the process of pre-freezing, showed a reduction in the drying time of the apple slices from 16.00 h to 14.17 h and an increase in the rehydration rate of the dried products by 17.99%, compared to the conventional group. The b* value of dried apple slices decreased from 28.24 to 22.98, and the color became white. The dried apple slices acquired moderate crispness and good chewiness, and the sensory evaluation was good. This study provides a reference for optimizing the parameters for the vacuum freeze-drying of apple slices and the development of new fruit slices.