超声预处理对真空冷冻干燥猕猴桃片品质的改善作用

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

目的 探究超声预处理对真空冷冻干燥猕猴桃片品质的改善作用。方法 分别采用不同功率(60、120、180、240、300W)和时间(1、5、10、15、20min)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60~180 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1~10min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、糖酸比均略有提高,但维生素C含量平均下降9.66%。超声预处理降低真空冷冻干燥猕猴桃片的水分活度,60~300 W超声组的水分活度下降4.29%~20.86%;1~5min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*均下降,且多数超声组的a*显著下降(P<0.05),其中300W超声波使a*下降20.95%,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120~240W和时间1~5min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。

Objective To explore the effects of ultrasonic pretreatment on improving the quality of vacuum freeze drying kiwifruit slices.Methods Kiwifruit slices were prepared by vacuum freeze drying after ultrasonic pretreatment with different powers(60,120,180,240,300 W) and time(1,5,10,15,and 20 min),the moisture,soluble sugar,titratable acid,vitamin C content,moisture activity,and color of the vacuum freeze drying fruit slices were analyzed,and the effects of ultrasonic pretreatment on the quality of the vacuum freeze drying fruit slices was explored.Results The moisture content of the vacuum freeze drying kiwifruit slices increased by 2.51%-13.70% when the ultrasonic power was 60-180 W;the moisture content increased by 9.23%-11.75% when the ultrasonic time was from 1 to 10 min.Compared with the blank group,the soluble sugar content,and sugar acid ratio were slightly increased in all ultrasonic groups,but the vitamin C content was decreased by 9.66% on average.Ultrasonic pretreatment reduced the water activity of vacuum freeze drying kiwifruit slices,and the water activity of the 60-300 W ultrasonic group decreased by 4.29%-20.86%;the water activity of the vacuum freeze drying kiwifruit slices in the 1-5 min ultrasound group was decreased by 4.91%-15.34%.The a* of all ultrasound groups were decreased,and the a* of most ultrasound groups were significantly lower than those of the blank group(P<0.05),among them,300 W ultrasound reduced the a* by 20.95%,and the color of the ultrasonic lyophilized fruit slices was greener.Conclusion Before vacuum freeze drying processing,ultrasonic wave with power of 120-240 W and time of 1-5 min is used for pretreatment on kiwifruit,which is helpful to improve the overall quality of kiwifruit slices in vacuum freeze drying.