| PEF technology is a novel non-thermal processing technology in food processing. A laboratory scale PEF system, inactivation of microorganism and enzymes, and effect on the quality of freshly-squeezed apple juice by PEF were investigated, the conclusions were made as follows.(1) A laboratory scale PEF system was designed and constructed and optimized complying with experimental requirements, its pulsed wave was a decaying waveform, volume of treatment chamber was 5mL, gap between electrodes was 10 mm, max. of pulsed electric field strength was 30 kV/cm.(2) The inactivation of E. coli and S. cerevisiae by PEF increased with the increase of applied electric field strength and pulse number. E. coli was more resistant than S. cerevisiae with same parameters of PEF treatment. 3.97 log cycle reduction of E. coli and 4.50 log cycle reduction of S. cerevisiae was achieved after 1449 pulses of 25 kV/cm in the plate-plate electrodes, respectively, and 3.76 log cycle reduction of E. coli and 4.11 log cycle reducticii of S. cerevisiae was achieved after 1449 pulses and 1242 pulses of averaged 25 kV/cm in the co-axial electrodes, respectively. D-value of E. coli was bigger that of S. cerevisiae responding to the same electric field strength and their D-value decreased with the increase of applied electric field strength, D-value decreased from 16666.67 us and 3333.33 us to 769.23 us and 500 us, respectively.(3) Ecof E. coli was decreased with the increase of pulses based on Hulsheger I model and Peleg model, and Ec of E. coli in the plate-plate electrodes is smaller than Ec in co-axial electrodes. For plate-plate electrodes and co-axial electrodes Ecof E. coli was from 7.24 kV/cm and 4.06 kV/cm to 5.12 kV/cm to 1.61 kV/cm according to HOlsheger I and from 12.47 kV/cm and 8.04 kV/cm to 6.96 kV/cm and 2.57 kV/cm according to Peleg model, respectively. nc of E. coli and S. cerviase was decreased with the increase of applied electric field strength based on Hiilsheger II model. In the plate-plate electrodes nc of E. coli and & cerviase decreased from 144 and 137 pulses to 18 pulses and 50 pulses, respectively, and in the co-axial electrodes nc of E. coli and S. cerviase from 173 and 156 pulses to 3 pulses and 0.05 pulses.(4) The -lnS measured experimentally and the -lnS projected by Hiilsheger I model had a closer correlation, the regressive coefficient R2for E. coli was 0.9305 and 0.9617, the regressive coefficient R2 for S. cerviase was 0.7981 and 0.9317 in the plate-plate electrodes and co-axial electrodes, respectively.(5) Cell death of E. coli and S. cerevisiae was probablely caused by the combination of cell membrane rupture, cytoplasm clumping and loss of cytoplasm. The cell's structure of E. coli and S. cerviase had a markedly change with surface roughing, cytoplasm shrinkage, uneven distribution, cytoplasm clumping, and plasmolysis. Moreover, for E. coli local membrane blurry and loss of most or all cytoplasm occurred with cell membrane only left, and for S. cerevisiae an increase of bud scars existed with TEM after PEF treatment. Shape change of some cells for E. coli and S. cerviase was observed with cytoplasm outflow and for S. cerviase more bud scars occurred with SEM. Asignificant increase of cells of E. coli and S. cerviase stainted by PI was observed with the use of fluorescent microscope after PER(6) Activity of HRP and PE decreased with the increase of electric field strength and pulse number. PE was more sensitive to PEF than HRP in the plate-plate electrodes. The correlation between the residue activity of HRP and PE with electric field strength for 207 pulses was 0.90 and 0.988, and with pulse number with 25 kV/cm was 0.964 and 0.986, respectively. ZE value of HRP and PE was 34.3 kV/cm and 20.2 kV/cm in the plate-plate electrodes, ZE value of HRP 32.0 kV/cm in the co-axial electrodes,(7) Conformational change of HRP and PE after PEF was studied, the [ 6 ] and the intensity of two negative peaks at 208 nm and 222 nm at CD spectra of HRP decreased, indicating a loss of a-helix content...
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