Study On Microwave Vacuum Drying On Qualities Of Chinese Yam

Chinese yam was one of the most important Chinese medicines which have dual-purpose of medicine and food, and it was best of all"four huaiqing Chinese medicines". Chinese yam was rich in saponins, phlegmatic, sugar, protein, yam element, choline, dopamine, mannan, phytic acid, allantoin, crude fiber, pectin, amylase, such as trace elements. Drying was an important method to preserved Chinese herbal medicine deteriorated. Microwave vacuum drying combines the advantages of microwave and vacuum, one was faster, shorten time, high energy efficiency and easy to control in microwave, the other one can reduce the water evaporation temperature, make it quickly evaporate at a low temperature. In order to improve the quality of huaiqing yam, solve processing and fresh problems, and promote the development of huaiqing yam industry, in this paper, the method of microwave vacuum drying of yam was used to research the drying characteristics and study quality were explored. The main conclusions are as follows:1. Drying characteristics and drying quality of the qualities of Chinese yam were studied that used the three drying method of hot air, vacuum and microwave. Test results show that the drying rate was fastest, Material deformation degree was lowest, rehydration rate was highest, Polysaccharides rate was the highest in microwave drying; drying rate was the slowest, Colour and lustre was best, rehydration rate was the worst in vacuum drying; Colour and lustre was the worst, the appearance deformation was most serious, Polysaccharides rate was the lowest in hot air drying.2. The Chinese yam was dried using the microwave vacuum dry, the drying characteristics and drying quality of the qualities of Chinese yam were studied in different drying conditions, and the thin layer of microwave vacuum drying mathematical model of Chinese yam was established. Test results show that the increase of microwave power rised gradually, the improvement of vacuum increased gradually, but the thickness had little effect on the drying process in the drying process of microwave vacuum drying; The three dry factors have significantly affected on dry quality; The thin layer of microwave vacuum drying mathematical model of Chinese yam was established, and the model applicable scope was that loading capacity was 300 g, thickness was 6 mm, -0.08 MPa≤vacuum≤-0.02 MPa, 800 W≤microwave≤2400 W.3. The regression experiment of the second general rotation design was employed, combination drying with microwave and vacuum tests of Chinese yam was studied, and regression equation of polysaccharides rate and drying time were established, then significant test was carried out. Obtained the optimal processing parameters was the polysaccharides yield was the highest (10.16%) when the vacuum pressure, microwave power and slice thickness were 0 Mpa, 2400 W and 10 mm respectively; the saponins yield was the highest (0.53%) when the vacuum pressure, microwave power and slice thickness were -0.08 MPa, 1600 W and 2 mm respectively; the rehydration rate was the highest (78.26%) when the vacuum pressure, microwave power and slice thickness were -0.04 MPa, 2400 W and 2 mm respectively.