Study On Effect Of Ultra-high Pressure Processing On The Sterilization Of Raspberry Juice

In the interest of eliminating adverse effects on nutrients and flavor of rasperberry by the traditional heat sterilization, inactivation experiments were done treated by ultra-high pressure (UHP) processing in order to overcome the lack of heat sterilization. Our target is to obtain the processing method and prametersof a variety of inactivation of microrganisms in raspberry juice and giving some references to the rasperberry processing.In the first, the effect of pressure and holding pressure time on inactivation of the mildew and yeast, E. coli, salmonella in the fresh raspberry juice were investgated.It was showed that:the higher the pressure, sterilization effect is better; with holding pressure time become longer, the lethal effect to these microorganisms become stronger. However, the effect of holding pressure time is weaker than the pressure. If holding pressure time become beyond certain range,the effect was little to extend holding pressure time. At room temperature (30℃)under pressure 200MPa and holding pressure time is 5.0min, E. coli was totally killed. Under pressure 300MPa and holding pressure time is 15.0min, Salmonella was totally killed. Under pressure 400MPa and holding pressure time is 15.0min, mildew and yeast was totally killed.Furthermore, in according to the survival curve of salmonella, the inactivation kinetics of salmonella was investigated.It was showed that the experiment data of inactivation of salmonella fitted well to Weibull model and Log-logistic model, and Log-logistic model has better performances in all aspects of eavaluation.Expriments of inactivation of natural microflora by ultra-high pressure processing were did..It was showed that under the pressure of 500MPa and holding pressure time is 25.0min, although the micro-organisms in the juice were not completely killed, but the total number of colonies can be reduced to<10cfu/ml, which meet the criterion of National Food Hygienic Standard of China(NFHSC). By variance analysis and response surface analysis, it was showed that pressure is the most influential factor, while temperature comes next and the holding pressure time is the least influential factor,In the end, effect of UHP on sensory evaluation was also investigated. It was showed that the sensory quality, soluble solids and pH value of juice treated by ultra-high pressure processing is close to the fresh raspberry juice, so treating raspberry by ultra-high pressure processing is a meaningful way to solve problem of rasperberry storage.