Experimental Study On Vacuum Freeze-drying Of Astragalus

The drying of Chinese medicinal materials has become an important content in the dry field of agricultural products, with the development of technology there are a growing number of drying methods of Chinese medicinal materials, every drying method has its own advantages and disadvantages. There is a contrast experiment analysis of six different drying methods of astragalus, and there is a optimization experiment analysis of the process parameters to the vacuum freeze-drying method by response surface design.The following is the main contents and conclusions:1. There is an experimental analysis and comparison of the effect of vacuum freeze-drying, vacuum drying, microwave drying, hot-air drying, drying in shade and drying in the sun on the rehydration ratio, value of chromatism, contraction percentage, microstructure and the content of effective components. The test results show that:(1)The rehydration ratio of astragalus with vacuum freeze-drying are the biggest, the next are vacuum drying, drying in shade, microwave drying and drying in the sun, the smallest is the astragalus with hot-air drying.(2)The smallest value of chromatism is the vacuum freeze-drying, the next are vacuum drying and hot-air drying, the color of astragalus with microwave drying, drying in shade and in the sun brown seriously.(3)The contraction percentage of astragalus with vacuum freeze-drying is the smallest, the nest are vacuum drying, hot-air drying, microwave drying and drying in the sun, the biggest contraction percentage of astragalus is the method of drying in shade.(4)The organization structure of astragalus after vacuum freeze-drying are loose and uniform, the drying method maintains the original state of the organization structure, there are different degrees of destruction of the organization structure with other drying method, causing the collapse of the organization structure.(5)Vacuum freeze-drying can retain the effective components of astragalus fully, the next are vacuum drying and microwave drying, while the content of effective components with the drying method of hot-air are the least2. The vacuum freeze-drying method was carried out optimizing test of technology parameters by using response surface design, the experimental factors are temperature of the heated plate, the pressure of the drying box, the thickness of the astragalus slice. The response value are energy consumption per unit of water, the value of chromatism, rehydration rate. Put the three response value together by using the weighted coefficient distribution, then using SAS software to carry out the data processing to get the best integrated response value and the optimal solution. The following are the results:The influence of the heating plate temperature on the integrated response value is the most obvious, the next is the thickness of the astragalus slice, the effect of the drying box pressure on the integrated response value was not significant. The process parameters when the integrated response value is the best in the range of the test is that:the temperature of the heating plate is 75.2467℃, the pressure of the drying box is 49.6629Pa, the thickness of the astragalus slice is 3.4152mm,at this time the energy consumption per unit of water is304.849 MJ·g-1, the value of chromatism is 45.8091,the rehydration rate is 2.3475.