Effect of infrared drying temperature on the drying characteristics and quality of jujube with ultrasonic pre-treatment

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. ©, 2015, South China University of Technology. All right reserved.