超声处理对中短波红外干燥红枣时间及品质的影响

为提高红枣干燥品质，减少干燥时间，以干燥时间为响应值，响应面优化得到红枣中短波红外干燥前超声处理条件为：频率40 kHz、时间40 min、功率350 W。最优超声处理后中短波红外干燥红枣至其干基含水率约为40%时所需干燥时间为9.55 h；未超声处理中短波红外干燥需13.33 h；传统热风干燥需17.13 h。扫描电镜观察红枣果皮，超声处理40 min使果皮表面产生大量裂缝，表皮层变薄，仅38.8 μm，表皮层和亚表皮层易分离，利于干燥过程中水分扩散，显著缩短中短波红外干燥时间。红枣超声处理后中短波红外干燥的干制品品质显著优于未超声处理红外干燥，极显著优于传统热风干燥。最优超声处理条件结合中短波红外干燥，所得干制品在3 种处理方式中总VC、总酚、总黄酮含量最高，糖酸比最高，色泽最优，能耗最少，是适合红枣干燥的技术方法。

Impact of Ultrasonic Treatment on Drying Time and Quality of Red Jujubes Dried by Medium-and Short-Wavelength Infrared Radiation

In order to improve the quality of dried products and reduce the drying time, red jujubes were subjected
to ultrasonic treatment before medium- and short-wavelength infrared drying. The optimal conditions for ultrasonic
pretreatment determined by response surface methodology were 40 kHz, 40 min and 350 W. The drying time to reach
a moisture content of 40% by medium- and short-wavelength infrared radiation was 9.55 and 13.33 h with and without
ultrasonic pretreatment, respectively, while the drying time for untreated samples by traditional hot air drying was 17.13 h.
After ultrasonic treatment for 40 min, red jujube peel produced a large number of cracks and became thin, only 38.8 mm in
thickness, and were easily separated into cuticular and epidermal layers, which was advantageous for moisture diffusion in
the drying process and reducing the drying time of red jujube dried by medium- and short-wavelength infrared radiation.
The quality of jujube products dried by medium- and short-wavelength infrared radiation after ultrasonic treatment was
significantly better than that of those without ultrasonic treatment and that obtained by traditional hot air drying. Jujubes
dried by infrared radiation after ultrasonic treatment contained the highest contents of total vitamin C, total phenols and total
flavonoids and the highest sugar/acid ratio, had the best color, and required the lowest energy consumption. Thus, infrared
radiation after ultrasonic treatment is an appropriate method for jujube drying.