红外温度对超声处理红枣的干燥特性及品质影响

Effect of Infrared Drying Temperature on the Drying Characteristics and Quality of Jujube with Ultrasonic Pre-treatment

摘要:

为提高红枣干燥品质，减少干燥时间。不同温度下（50、55、60 ℃）中短波红外分别干燥超声处理和未超声处理的红枣，对比传统分段热风干燥，研究不同干燥方法对红枣的干燥特性及品质的影响。结果表明：比较传统分段热风干燥，随温度增加，中短波红外干燥未超声处理红枣的干燥时间减少6.67~13 h，能耗减少7.05~13.05 kW?h，而超声处理红枣的干燥时间减少9~13.67 h，能耗减少9.67~14.93 kW?h。随着中短波红外干燥温度的增加，干燥速率提高，能耗降低。中短波红外干燥过程中，红枣内外温度迅速达到设定温度，表面温度高于内部温度，水分在表皮易汽化，干燥速度快，褐变小，营养成分损失少。综合评判7种干燥方法，50 ℃中短波红外干燥超声处理的红枣，干燥能耗较低，糖酸比最高，总维生素C、总黄酮、总酚含量较高，咀嚼性最好，褐变最少，色泽和外观质量最好，是较好的红枣干燥方法。

Abstract:

In order to improve the quality of dried jujube and reduce the drying time, medium-short wave infrared radiations at different temperatures (50, 55, and 60 ℃) were utilized to dry jujubes with and without ultrasonic treatment. Compared with the traditional multi-stage air-drying, the effects of different drying methods on the drying characteristics and the quality of jujube were analyzed. The results showed that compared with the traditional multi-stage air-drying, the drying time and energy consumption for drying the jujube with no ultrasonic treatment but by medium-short wave infrared radiation were reduced to 6.67~13 h and 7.05~13.05 kW?h, respectively, while the jujube subjected to ultrasonic treatment were reduced by 9~13.67 h and 9.67~14.93 kW?h, respectively. With increasing medium-short wave infrared drying temperature, the drying rate increased and energy consumption decreased. During the medium-short wave infrared drying process, both the internal and external temperatures of jujube quickly reached the setted temperature, and the surface temperature was higher than the internal temperature. Moisture from the skin easily vaporized, the degree of browning was low, and small amounts of nutrients were lost. Seven kinds of drying methods were comprehensively evaluated. Compare to all the drying methods, when the jujube was dried by medium-short wave infrared radiation at 50 ℃, the drying energy consumption was low, the sugar acid ratio was the highest, the contents of total vitamin C, total flavonoids, total phenols were relatively high, and chewiness, color, and appearance quality were the best, while the degree of browning was the lowest. Therefore, these conditions were identified as a good method for drying jujube.