Quality kinetics of microwave and pasteurised processed tomato juice

To understand sterilization methods on the impact of the quality and shelf life of tomato juice, a kinetic study of post processing quality loss was conducted after microwave processing (800 W, 20 s) or thermal pasteurisation (85℃, 4 min) of tomato juice. Selection of processing conditions was only based on microorganism inactivation. Total plate count, Vitamine C, and colour changes were measured at intervals during storage under different isothermal conditions (0, 4, 10, 25, 37℃). The results indicated that the rates of increasing of total plate count, lossing of Vitamine C, the browing rate have increased with the increasing of storage time and temperature for both types of processing, and browing rate was linearly correlated to Vitamine C loss. Based on the remainder of Vitamine C 9.1-17.5 days shelf life for microwave treated tomato juice was longer than the respective values of thermally pasteurised juice at low storage temperatures (0-10℃) used, and based on the degree of browing the difference was 14.9-71 days. however, the difference between pasteurize and microwave sterilization method was not significant at 25-37℃. And based on the total plate count, there was no obvious difference, it was only one or two days. Microwave processing resulted in better retention of the quality of untreated juice and superior sensory characteristics compared to thermal pasteurisation. The remaining shelf-life of microwave treated tomato juice could be predicted at the storage temperature at 0-37℃ based on Vitamine C and the total plate count. It showed from the reliability assessment between predicted and observed shelf-life that accurate rate was within 90% calculated by the prediction model for the shelf-life of tomato juice. It was better to take the total number of colonies of tomato juice as the ultimate standard for shelf life. At low storage temperatures (0- 10℃) 5-8 days were proposed as the shelf life of microwave treated tomato juice, and 5-9 days were proposed as the shelf life of thermally pasteurized tomato juice. The results provide the technical basis for the application of microwave technology in processing and storage of fruit juice.