Sterilization Process Of Canned Pineapple By Radio Frequency Heating

Canned pineapple is the main processed product of pineapple. Canned pineapple not only maintains the taste of fresh fruit but also solves the storage problem. However, traditional sterilization method of can needs long heating time which leads huge loss of nutrients. To solve this problem, this test tries to take radio frequency(RF) technology into the canned sterilization technology to transform the traditional sterilization technique. RF heating has the potential to develop into a substitution for the traditional sterilization technique. RF heating food has the features of uniform heating and rapid sterilization to get high-quality products. In order to obtain the RF heating process for canned pineapple sterilization, this paper has carried on a system research.This paper preliminarily studies the RF heating process conditions. Specific contents are as follows:(1) Using the optical fiber probe and fluorescence optical fiber temperature measuring system, it monitors the temperature changes in canned during RF heating on-line and measures the temperature distribution of canned and finds out the hot and cold spots.(2) By changing the plate spacing, fruit size, initial sugar solution temperature, it improves the effect of the heating uniformity.(3) Comparing with the traditional water bath sterilization, the temperature rising characteristics and sterilization effect of RF sterilization are researched.(4) Measuring the quality after RF sterilization for canned pineapple, and comparing it with traditional water bath sterilization. The main conclusions are as follows:(1) The cold spot position of RF is different from cold spot position of traditional water bath heating. RF cold spots locates in the liquid sugar center at the bottom of the canned. The uniformity of the RF heating canned is poor. The temperature difference between the highest and lowest reached more than 15℃ at end of heating.(2)Water bath auxiliary RF heating can improve the heating uniformity, and the temperature difference is reduced to 7℃. The best parameters are the plate spacing at 210 mm, the quality of fruit piece at 12 g, initial sugar liquid temperature at 80℃.(3)When the cold spot temperature of RF heating reached to 80℃, it takes 3 min for RF heating, and 9 min for water bath heating, achieving the same sterilizing effect.(4) RF processed samples can maintain the hardness of pineapple, vitamin C retention rate, and color. The color change of water bath heating treatment is bigger. The ΔE * is 10, which has obvious differences, While the ΔE * of bath auxiliary RF heating is 3.19. It shows that pineapple can better keep the original golden after water bath auxiliary RF treatment. Pulp hardness and brittleness of water bath auxiliary RF treatment was obviously higher than that of water bath heating processing. The final hardness of water bath treatment is about 90 g, while water bath treatment of is still about 100 g. Vc in the pineapple of traditional heating have been destroyed, which the sample of the Vc retention rate is only 10.58%. Compared to the traditional heating system, the sample VC retention rate is significantly improved aquired by water bath auxiliary RF treatment, which reach to 64.67%.Accordingly, it is better to replace water bath heating sterilization with RF assisted water bath sterilization, and RF assisted water bath sterilization can significantly improve the quality of canned. Therefore, there is important meaning to use RF for the actual production process.