Studies On The Microwave Vacuum Drying Of Arillus Longan

Arillus Longan (alternate name cassia pulp) is arillus of Sapindaceae, Dimocarpus Longan Lour, which has high nutrition and medical function. Microwave vacuum drying (MVD)technology was applied to the process of Arillus Longan in this thesis. MVD Characteristics of Arillus Longan were studied, and optimal drying technology is searched for establishment of kinetic model for MVD of Arillus Longan. By systematically analyzing variation rule of quality change in the drying process of Arillus Longan, optimum process condition of MVD of Arillus Longan was determined. Meanwhile effect of different drying technique on quality characteristics of Arillus Longan was investigated. Objective of all above research was to offer the theoretical foundation for industrialized application of Arillus Longan process by MVD technology.1. The MVD equipment was used to research drying characteristics of Arillus Longan in this paper. Effects of microwave power, vacuum degree and load on the drying rate were also studied, by which the rule of moisture content change during the process of microwave vacuum drying was ascertained. The results indicated that drying process could be divided into three stages: acceleration, constant speed and deceleration. During the drying process, the higher microwave power and vacuum drgree and the less load was, the more frequent the rate of water loss and the less time the drying process needed.2. According to the drying characteristics of MVD, the drying kinetics model for Arillus Longan was established. The drying kinetics model satisfied with Page equation MR = e^-rtN, where r = e^{-3.3788 -0.0054L-0.0174V+ 0.2715P}, N= 1.4624 + 0.0011L+0.0076 V + 0.0686(R² =0.9998).It was proved that predicted datas were nearly accordant to experimental datas, and the change of moisture of Arillus Longan during the processes of MVD could be described accurately by this model.3. The effect of microwave power, vacuum drgree, and load on color change, content of polysacchardes and activity of SOD during MVD were studied. The content of polysacchardes declined with the increase of microwave power; while the content of polysacchardes increased with improving of vacuum drgree.With increase of loadage the content of polysacchardes climbed up firstly then declined. With low microwave power Arillus Longan showed a light yellow appearance and too high microwave power lead to a black burned result,a appropriate microwave power made Arillus Longan showed a brilliantly gloden color. The activity of SOD decreased with increase of microwave power,while increased with improving of vacuum drgree.With increase of loadage,the activity of SOD increased at first and then declined.4. The quadratic regression equations to describe color clearation, drying time, Arillus Longan polysaccharide contents and Specific Energy Consumption (SEC) for MVD were established by using two factors quadratic regression general rotary unitized design. Based the experimental data, effect of the interaction was analyzed to determine that microwave intensity and vacuum degree had significant influences on color clearation, drying time, polysaccharide contents and SEC.The optimal MVD technology for Arillus Longan was determined as follows: vacuum degree was -85kPa and microwave intensity was 6 W/g.5. Effects of four drying technologies, including hot-air drying, microwave drying, vacuum drying and MVD on the shrinkage, rehydration rate, polysacchardes content, activity of SOD and sensory quality were studied systematically. The results showed that: the shrinking percentage of hot-air and MVD was the highest, the second one was vacuum drying, the lowest was microwave drying. MVD had the highest rehydration rate, the second was vacuum drying, the third was microwave drying and the lowest was hot-air drying. The retention rate polysacchardes of MVD was the highest and the second one is vacuum drying, then hot-air drying while the microwave drying get the lowest retention rate polysacchardes. MVD had the highest retention activity of SOD.The second one is hot-air drying, then vacuum drying. Microwave drying had a great loss of SOD. The sensory evalution of MVD got the highest score, and the second was hot-air drying and vacuum drying, microwave drying got the lowest score. Based on an overall consideration of quality influences with different drying technologies.The comprehensive evaluation results showed that Arillus Longan had optimal quality by using MVD.