Study On The Technology Of Apple Blanching And Color Protection Using Radio Frequency Heating

China is one of the greatest world in apple production. Apple is mainly consumed in fresh. In recent years, apple processing industry is developing rapidly. Deep processed products of apple are growing day by day. Blanching is an important procedure in the process of product, such as jam, preserved fruit, juice, wine and chips. Blanching effect directly affects the quality of the product. Shortcomings, such as slow heating transfer, nutrition lost, great water consumption and difficult in sewage treatment exist in the traditional hot water and steam blanching.Radio frequency(RF) is a new type of heating method with the characteristics of deep heating penetration and high heating speed. There appeared a lot of researches in the aspects of drying, sterilization and disinsectization of nuts and grains using RF heating. And certain achievements had been obtained. Exploring RF heated blanching of apple is of great significance in improving the quality of processed products of apple.The extraction conditions and activity measurement methods of apple polyphenol oxidase(PPO) was studied in this article. The inactivation kinetics of apple PPO enzyme were studied by 27.12 MHz RF heating and traditional water bath. The changes of the micro and macro properties of apple slices were researched to explore the changing mechanism of apple slices after RF heating. The results were as follows:(1)The optimum absorption wavelength of the reaction of apple PPO enzyme and catechol was 410 nm. The activity of PPO was the highest with the ratio of extracting liquid and material 100 mL·g- 1, pH 7.0, extracting time 30 min. The reacting speed was the fastest of apple PPO enzyme with catechol at pH 5.2 and 30℃.(2)The decline of PPO enzyme activity with time showed a linear relationship and fitted the first order kinetics well by water bath heating. The Log-Logistic model and Dosed-Response model fitted apple PPO enzyme inactivation well by RF heating.(3)It showed that apple PPO enzyme solution could be heated the fastest under electrode gap of 115 mm and conductivity of 0.25 S/m. The heating curve of apple slices by RF heating was approximately linear. It could be heated fast with temperature higher in the middle and lower around the edge.(4)With the temperature increase of apple slices, the relative activity of apple PPO enzyme gradually declines. The curve showed as S type. Weight loss rate, hardness, L value and a value of apple slices regularly changed with temperature by RF heating.(5)The microscopic structure of the apple slices was observed with SEM before and after RF heating. The cytoplasm of fresh apple cell was surrounded by thick cell wall. After RF heating, parenchyma of apple cells collapsed, plasmolyzed, cell shrank and deformed and the cell wall burst. The microstructure of apple slices influenced and determined the change of external physical and chemical properties.