Effects of microwave-hot air drying process on quality and surface microorganism quantity of Lycium barbarum

In order to study the effect of microwave hot air drying on the quality and microorganism quantity of L. barbarum. In this paper, the microwave hot air drying method and the traditional hot air drying were used to dry L. barbarum. The main quality indexes of L. barbarum polysaccharide, total sugar, crude protein, crude fat were determined. The number of microorganism on the surface of L. barbarum was measured. Hot air drying refers to drying after alkali liquor dewaxing and hot air drying at a constant temperature of 50 ℃. Microwave hot-air drying means that the alkali liquor is dewaxed first and then dried, and the hot-air drying is carried out at a constant temperature of 50 ℃, and then dried by microwave (Power: 215 W, microwave pulse ratio: 1.67). When the moisture content reaches 80%, 50%, 30% and 10%, the samples were taken to determine the content of L. barbarum polysaccharide, total sugar, crude protein and crude fat. The total number of bacteria and Escherichia coli on the surface were determined. Staphylococcus aureus, Salmonella and Shigella were detected. The results showed that the loss rate of L. barbarum polysaccharide and total sugar was significantly different between microwave hot air drying and traditional hot air drying (P < 0.05). Compared with the traditional process, the combined drying process reduced 15.44 and 11.06 percentage points, 18.46% and 20.98% respectively. The loss rate of crude protein was 21.46% and 20.12% respectively, but the difference was not significant. The difference of crude fat loss rate was not significant, 10.56% and 12.29% respectively. In terms of sterilization rate, there was significant difference between the two processes (P < 0.05). The composite drying process was 91.26% and the traditional drying process was 82.25%. Dewaxing before drying could kill 65.24% of surface microorganisms. After drying, the bactericidal rate of composite drying process was 91.26%, which was 9.01 percentage points higher than that of traditional drying process. E. coli was used as the contaminating bacteria for artificial pollution test. After the combination of the two processes, the sterilization rate was 83.21%, which was 12.93 percentage points higher than the traditional hot air drying process. Therefore, compared with the traditional hot air drying process, microwave hot air drying process retains more nutrients of L. barbarum, has better sterilization effect, and is conducive to the quality and food safety of dried L. barbarum. However, the L. barbarum contaminated by E.coli after dewaxing could't be completely sterilized by microwave hot air combined drying process and traditional hot air drying process, so the existing technology needs to be improved or combined with other sterilization methods. The results provide a reference for the application and improvement of microwave hot air drying in the processing of L. barbarum.