超声预处理对真空冷冻干燥猕猴桃片品质的改善作用

目的 以“海沃德”猕猴桃为原料，采用超声预处理改善真空冷冻干燥猕猴桃片的品质。方法 分别采用不同功率（60 W，120 W，180 W，240 W，300 W）和时间（1 min，5 min，10 min，15 min，20 min）的超声波预处理猕猴桃，经真空冷冻干燥制成真空冷冻干燥猕猴桃片，分析真空冷冻干燥果片的水分含量、可溶性糖、可滴定酸、维生素C含量、水分活度、色度等指标，探讨超声预处理对真空冷冻干燥果片品质的影响规律。结果 超声功率为60 W~180 W时，真空冷冻干燥猕猴桃片的含水量提高2.51%~13.70%；超声时间为1 min~10 min时，含水量提高9.23%~11.75%。与空白相比，所有超声组的可溶性糖含量、可滴定酸含量、糖酸比均略有提高，但维生素C含量平均下降9.66%。超声预处理显著降低真空冷冻干燥猕猴桃片的水分活度，60 W~300 W超声组的水分活度下降4.29% ~20.86%；1 min~20 min超声组的真空冷冻干燥猕猴桃片水分活度下降4.91%~15.34%。所有超声组的a*值均下降，显著低于空白，其中300 W超声波使a*值下降25.08%，超声冻干果片颜色更绿。结论 猕猴桃在真空冷冻干燥加工之前，使用功率120 W ~240 W和时间1 min ~5 min超声波进行预处理，有助于改善真空冷冻干燥猕猴桃片的整体品质。

Improvement of quality of vacuum freeze drying kiwifruit slices by ultrasonic pretreatment

Objective To improve the quality of freeze drying kiwifruit slices, ultrasonic technology was used to pretreat kiwifruit slices. Methods Hayward kiwifruit slices were pretreated with different power (60 W,120 W,180 W,240 W,300 W) and time (1 min, 5 min, 10 min, 15 min, 20 min) of ultrasonic, then dehydrated by freeze drying. The moisture content, soluble sugar content, titratable acid content, Vc content, water activity and chromaticity of freeze drying kiwifruit slices were analyzed. Results The moisture content of freeze drying slices was increased by 2.51% ~ 13.70% when the ultrasonic power was 60 W ~ 180 W. When the ultrasonic time was 1 min ~ 10 min, the moisture content was increased by 9.23% ~ 11.75%. Compared with the blank group, the soluble sugar content, titratable acid content and sugar acid ratio were slightly increased by ultrasonic pretreatment, but Vc content of freeze drying slices was decreased by 9.66% on average after ultrasonic pretreatment. The water activity of freeze drying slices was decreased by 4.29% ~ 20.86% after 60 W ~ 300 W ultrasonic pretreatment. The water activity of freeze drying slices was decreased by 4.91% ~ 15.34% after 1 min ~ 20 min ultrasonic pretreatment. Compared with the blank group, the a* value of freeze drying slices was decreased significantly after ultrasonic pretreatment, and the a* value was decreased by 25.08% after 300 W ultrasonic treatment. the freeze drying slices were greener by ultrasonic pretreatment. Conclusion All showed that pretreatment with 120 W ~240 W and 1 min ~5 min ultrasonic was helpful to improve the overall quality of freeze drying kiwifruit slices before freeze dried.