| Title:Study on Non-thermal Inactivation of Peach Juice by High Intensity Pulse Electric FieldMajor:Agricultural Product Processing and Storing EngineeringSupervisor:Professor Yongguang Yin, Jilin UniversityThe many problems that the factories have met were resulted from theuncompetent quality produced by microbes'pollution during food production.Many kinds of inactivation methods have been used, but it was important thathow we could inactivate the microbes utmost in the condition of saving energyand reducing environment pollution. The paper has elaborated the problems thatwe should notice during inactivation combined with the inactivation condition ofhome and abroad. It included that ①determined the inactivation temperatureand time based on PH value; ②determination of inactivation condition; ③theheat transfer problems of food heating; ④noticed the original number ofmicrobes and spores; ⑤food component and inactivation; ⑥the association ofdifferent temperature and time; ⑦the inactivation choices before and afterpacking; ⑧the cooperation effect of different methods.The inactivation was the most crutial technology during fruit juiceproduction. The traditional method was inactivated by heating, but if thetemperature was lower, it would result in corruption of product; if the temperaturewas too high, it would destroy the nutrition component, make the flavor bad, andresult in quality decreasing of product. Therefore, the inactivation technologieswhich could inactivate microbes efficiently, save energy, raise the nutrition andsensory quality of product and attain the required product index have emerged asthe times required.In order to find out the most effective and most safe method of inactivation,the paper has analyzed and compared the inactivation mechanic, efficiency,shortage and advantage of present domestic and international general foodinactivation method, including food resistance heating technology, microwaveinactivation technology, superhigh pressure inactivation technology, high intensityelectric field (PEF) inactivation technology, radiate inactivation, pulse strong lightinactivation and photocatalytic technology of sterilization. The inactivationsystem of PEF has been analyzed and designed through analyzing the inactivationmechanics and major effect factors of PEF. Furthermore, a series of experimentshave been carried out to inactivate the Escherichia Coli in the peach juice throughorthogonal experiment, the regression equations between microbe remains andPEF strength, pulse number, inactivation temperature have been got. Finally, thequality of the peach juice has been analyzed from the aspect of sensory qualityassessment, total acid, Vc, total sugar, aminonitrogen, electrical conductivity andviscosity. The influences of PEF on the quality of peach juice during storage havebeen studied. The major content and conclusions were as following:1. The conclusions have been reached through studying on influence of PEFstrength, pulse number and temperature on the inactivation effect of PEF, and thenumber of microorgansims in initial fruit juice was 5.0×107 cfu/mL. Theconclusions were as following:(1) In the condition of 4 pulses and room temperature, we modified different electric field strength (70 kV/cm,60 kV/cm,50 kV/cm,40 kV/cm,30 kV/cm, 20 kV/cm,10 kV/cm) to process peach juice. And it has been found that the inactivation effect of PEF on peach juice increased with the increase of PEF strength, the corresponding regression equation wasy = 1E-09x16 -2E-07x15 + 1E-05x14 -0.0004x13 + 0.0059x1 -0.0429x12 + 7.7(R12 = 1);(2) In the condition of PEF strength 40 kV/cm and room temperature, we modified different pulses number (2, 4, 6, 8, 10, 12) to process peach juice. And we have found that the inactivation effect of PEF on peach juice increased with the increase of pulse number, and the corresponding regression equation was y = 9E-05x26 -0.0036x25 + 0.0525x24 -0.3651x23 + 1.2353x22 - 1.9997x2+ 7.7(R22 = 1);(3) In the condition of 4 pulses and PEF strength 40 kV/cm, we modified different electric treatment temperature (20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃) to process peach juice. It has been found that the inactivation effect of PEF on peach juice increased with the increase of inactivation temperature, and the corresponding regression equation was y = -3E-06x35 + 0.0005x34 -0.0333x33 + 1.0324x32 -15.728x3 + 100.7(R32 = 1);2. Orthogonal test was carried out by chosing three reasonable levels of electricfield strength, pulse number and treatment temperature respectively, the microbes'number in initial peach juice was 5.0×107 cfu/mL. The conclusions were: thePEF strength and sterilization temperature were notable factors while handlingpeach juice with PEF in which the PEF strength was the most important factorand its significant level was 0.01, the significant level of treatment temperaturewas 0.05. The significant level of pulse number was 0.25, so pulse number wasnot notable factor. The best level of PEF strength, treatment temperature and pulsenumber were 60kv/cm, 40 ℃and 6 respectively.3. In the condition of PEF strength 40 kV/cm, pulse number 6 and roomtemperature, the juice of which concentration was 20%, 40%, 60%, 80%, 100%respectively was inactivated with PEF. The microbes'number in initial peachjuice was 5.0×107 cfu/mL. The conclusion was that microbial survivors increasedwith the increase of the concentration of peach juice. We could conclude that PEFhas more efficiency on the solution with lower electric conductivity.4. The relation between inactivation effect of different juice (with theconcentration of 20%, 40%, 60%, 80%, 100% respectively) and the parameters ofhigh intensity electric field has been researched. The relation curves betweeninactivation effect of different concentration peach juice and PEF strength, pulsenumber and treatment temperature respectively were got. The microbes'numberin initial fruit juice was 5.0×107 cfu/mL.(1) In the condition of 4 pulses and room temperature, PEF strength waschosen 10 kV/cm,20 kV/cm,30 kV/cm,40 kV/cm,50 kV/cm,60 kV/cm,70 kV/cm to process peach juice. The conclusion was that the microbes'surviorsin all kinds of juices decreased with the increase of PEF strength, in the conditionof the same PEF strength, the microbes surviors increased with the increase of theconcentration of peach juice.(2) In the condition of PEF strength 40 kV/cm and room temperature, thepulse number was chosen 2, 4, 6, 8, 10, 12 to process peach juice. The conclusionwas that the microbes'surviors in different concentration of peach juice decreasedwith the increase of PEF strength. In the condition of the same pulse number, themicrobes'surviors increased with the increase of the concentration of peach juice.(3) In the condition of PEF strength 40 kV/cm and pulse number 2, thetemperature was chosen 45 ℃,40 ℃,35 ℃,30 ℃,25 ℃,20 ℃to process peachjuice. The conclusion was that the microbes'surviors in all concentrations ofpeach juice decreased with the increase of temperature. In the condition of thesame inactivation temperature, the microbes'surviors increased with the increase...
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