| As the standard life of people is rising, the requirement of consumers for food isimproving. The consumers need healthy, fresh and nutritional food. Milk is recognized thenutritional food all over the world, it contains not only protein and calcium, butalso all vitamin that needed by people and kinds of immunity alive gene. It'snutrition value is most closed to the perfect food, and it has been praised whiteblood. At present, milk is kept by inactivating microbes and killing enzyme. Themethod of inactivating microbes and killing enzyme for fresh milk in domestic ismainly heat processing. The heat treatment exist many problems that can't besolved, such as it influences the color, favor and function of fresh milk, and it alsodestroys nutrition composition of milk. Therefore, it is necessary to find a newmethod of inactivating microbes and killing enzyme that not only prolongs storageperiod, and keeps its nutrition value, but also saving energy consume.In order to keep the nutrition composition as much as possible, the hightemperature short time sterilization was used in industry, but it destroyed thenutrition more or less. Pulsed electric field (PEF) is one of the non-thermal processtechnologies. Effectiveness of pulse electric field (PEF) compared to thermalprocessing is well established for the inactivation of different microorganisms aswell as minimization of losses in volatile compounds and color in the course ofprocessing and storage. In order to prolong its storage period, keep the flavor to thebest extent. The research did a lot of experiments, the main work were introducedas following:1. The conclutions have been reached through Single factors experimentanalysis by studying influence of PEF strength, pulse number and temperature onthe inactivation effect. It was obviously found that Bacterial counts decreased withthe electric field strength, as previously found in most investigations. Effects ofdifferent electric fields strength differed in the bacteria inactivation in samples(P≤0.05);the bacterial survivals decreased with the increasing of number of pulses,however there were no significant differences (p≥0.05) in bacterial survivals ofsamples treated with different pulses number while in the same electric fieldstrength and temperature;there were statistical significant differences (p≤0.05)between samples treated with different temperatures. The higher the treatmenttemperature was, the better the inactivation effect was.2. In order to study the sensitivity of each factor to inactivation effects, wechose three reasonable levels of electric field strength, pulse number and treatmenttemperature respectively, and carried out orthogonal test based on orthogonal testtable L9 (34). The conclutions were as following: when we handled milk by PEF,electric field strength and treatment temperature were notable factor, among whichthe electric field strength was the most important factor and its significant level was0.01. The significant level of treatment temperature was 0.01 too, and that of thepulse number was 0.1. The best level of electric field strength, pulse number andtemperature were 70kv/cm,6,70℃ and the corresponding regression equation wasy=0.0816z1+0.034z2+0.061z3-1.23, after fitting inspect, the regression equation hasbeen proved reliable.3. The critical time that the Peroxidase was totally inactivated wasrespectively measured in the condition of different temperature and no PEFtreatment. The results were: while the temperature were 60℃,70℃,80℃,90℃,100℃ , the critical time were 30min,8.5min,3min,0.5min,0.11min respectively.Temperature has notable effect on killing enzyme, but it need longer time, then theheat treatment not only increased the treatment cost, but also destroyed the qualityof milk samples.4. When the samples were processed by PEF only, the effect of PEF onenzyme increased as the PEF strength and pulse number arised. The inactivationrate of peroxidase increased with PEF strength. While the PEF strength rangedfrom 30 kv.cm-1 to 60 kv.cm-1, the inactivation rate of peroxidase increased faster,and while the PEF strength ranged from 60 kv.cm-1 to 90 kv.cm-1,the inactivationrate of peroxidase increased slowly;inactivation rate of peroxidase increased withpulse number. When the pulse number was less than 10, the inactivation rate ofperoxidase increased faster, and when the pulse number was more than 10, theinactivation rate of peroxidase changed hardly. Since the more pulse number was,the longer the treatment time was, in order to inactivate the peroxidase well andshorten the treatment time, so 10 pulse number was chosen to process milk in thisresearch.5. When milk is processed by the method that combined PEF technology withpasteurization, all problems that the conventional heat processing can't solve canbe solved properly, that is the microbes and enzymes in milk can be completelyinactivated in the lower temperature. The result shows that in the aspect ofsterilization, PEF plays an important role, while the temperature gives auxiliaryfunction;in the aspect of killing enzyme, the temperature plays an important rolewhile PEF gives auxiliary function.6. The minimum PEF intensity and processed time in different temperaturehave been found by a series of Single factors experiment analysis in this research,and the losses of milk nutrition in different treatment condition have beenmeasured, the nutrition losses of milk except vitamine C processed in lowertemperature but higher PEF strength are much less than that of milk processed inhigher temperature but lower PEF strength, while vitamine C was relative with heattreatment time,the longer treatment time was, the more nutrition loss was. As thetreatment temperature was high, the nutrition loss of milk was more, while thetemperature rised from 70℃ to 90℃, the loss of protein increased four times,vitamine B2 increased 1.5 times. Meanwhile the nutrition composition of milksamples treated in the critical condition would not change with time. Therefore, themethod that combined PEF technology with pasteurization could solve theproblems that brought by enzyme after treatment.
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