Inactivation Of Escherichia Coli In Fresh Cucumber Juice And A Shelf Life Study Using High Hydrostatic Pressure

High pressure is a technology that using the special liquid as pressure transmission medium and processing the food with 100-1000MPa pressure. This technology can kill microorganisms and inactivate food quality related enzymes and extend product shelf-life.The objective of this work was to study the sterilizing and preservation effect in fresh cucumber juice.The main contents are:(1) study on the relationship between the experiment parameters(pressure and holding time) and the sterilizing effect after inoculated E.coli.Then estabilish sterilization kinetic model. (2) After squeezing juice and treatment,cucumber juice stored up in three temperatures.Then study on the preservation effect.The main conclusions are as follows:The first one:Sterilizing Effect of Fresh Squeezed Cucumber Juice(1)When holding time is constant,the sterilization effect of high pressure gradually strengthen following pressure rise.And the effect is not a linear relation with pressure.When the temperature is ambient temperature(25℃),and the holding time is 2min;200MPa and under pressure almost has no influence on the microorganisms.In contrast,when pressure riseing to 600MPa there is no microorganism. (2)The model parameters in VRBA(Violet Red Bile Agar) is different from those in BHIA(Brain Heart Infusion Agar).The D value and zp value are smaller in VRBA,while the velocity k and volume change of activation are larger.(3)Pre frozen samples shows a synergistic effect which increasing its susceptibility to high pressure.This sample's velocity k is larger than common samples and D value is smaller.The second one:Preservation Effect of Fresh Squeezed Cucumber Juice(1)High pressure and thermal processing can extend the shelf life of cucumber juice, but these processing have a impact of a different degree in cucumber juice. And the effect of high pressure processing is better than the effect of thermal processing.(2)Both high pressure and thermal processing could affect the color of cucumber juice; and with the extension of storage time, the L value and total color difference are getting worse. But the processed samples'rate of change is less than the raw samples'.And the effect of thermal processing is similar to the effect of 500MPa processing.(3)The samples has been processed by high pressure or heat show increase at first then turn to be decrease in pH value. And the pH value of processed samples is larger than the raw samples.The pH value of thermal processing is similar to the value of high pressure processing.(4)The soluble solid content of processed samples is almost no change. The centrifugal sedimentation of thermal processing samples is the worst, the high pressure processing samples is next, and the raw samples is the best.When storage temperature is 10℃,centrifugal sedimentation rate of the thermal processing samples after storing up 10 days is similar to the high pressure samples after storing up 15 days; When storage temperature is 25℃,centrifugal sedimentation rate of the thermal processing samples after storing up 56 hours is similar to the high pressure samples after storing up 64 hours; When storage temperature is 37℃,centrifugal sedimentation rate of the thermal processing samples after storing up 20 hours is similar to the high pressure samples after storing up 24 hours.