马铃薯超声强化冷风干燥及品质特性

为探讨直触式超声对马铃薯冷风干燥的强化效应，利用超声-热泵式冷风干燥设备进行干燥实验，研究不同超声功率及冷风温度对马铃薯干燥过程、微观结构及主要营养成分的影响。结果表明：提高超声功率及干燥温度能够明显缩短马铃薯所需干燥时间，较低温度下的超声强化效果优于较高温度；马铃薯超声强化冷风干燥呈先恒速、后降速的干燥过程，表明该干燥过程由表面扩散控制转化为内部扩散控制；超声强化能够增大和增多物料表面的微细孔道，从而有利于水分传递；Weibull分布函数可很好地拟合马铃薯超声强化冷风干燥过程，利用该模型计算所得的估算水分扩散系数Dcal随着干燥温度和超声功率的升高而增大，表征干燥时间的尺度参数α则随着超声功率的升高而减小；冷风温度和超声功率对干燥产品的总酚、总黄酮、VC含量有显著影响（P＜0.05），在冷风干燥过程中施加超声辅助处理有利于提高营养成分含量。利用层次分析法计算得到的优化参数为干燥温度10 ℃、超声功率48 W时，对应的总酚、总黄酮、VC含量分别为296、52、96 mg/100 g。因此，将超声强化技术用于马铃薯冷风干燥中能够显著缩短干燥时间并有效保护产品品质。

Drying Characteristics and Quality of Potato Slices Subjected to Ultrasound-Assisted Cold Air Drying

In order to investigate the enhancing effect of ultrasonic treatment on cold air drying of potato slices, an ultrasonic-assisted heat pump cold air dryer was applied to explore the influence of ultrasonic power and drying temperature on the drying process and the microstructure and several major nutritional components of dried potato slices. The results showed that the drying time was reduced significantly by increasing either ultrasonic power or drying temperature and that drying enhancement was more remarkable at a lower drying temperature than at a higher temperature. The drying rate initially remained constant and then declined during the ultrasonic-assisted drying process, indicating transformation from surface diffusion control to internal diffusion control. The application of ultrasonic treatment could enlarge the size and number of micro-channels on the material surface, being beneficial for moisture transfer. The Weibull distribution function could fit the drying process with high precision. The estimated value of moisture diffusion coefficient increased with increasing drying temperature and ultrasonic power, whereas the value of scale parameter α, characterizing the drying time, decreased with the increase in ultrasonic power. Both ultrasonic power and cold air temperature had significant effects on the contents of total phenols, total flavonoids and vitamin C in dried potato products (P < 0.05). It is clear that the application of ultrasonic treatment to cold air drying of potato slices can increase the contents of major nutritional components. The analytic hierarchy process was applied to obtain the optimal parameters as follows: drying temperature 10 ℃ and ultrasonic power 48 W, and the contents of total phenols, total flavonoids and vitamin C in dried potato slices prepared under these conditions were 296, 52 and 96 mg/100 g, respectively. Therefore, the application of ultrasonic treatment to the cold air drying process of potato slices can remarkably shorten the drying time and improve the product quality.