Study On The Effects Of High Pulsed Electric Fields To Activity And Structures Of POD

Pulsed electric field (PEF) is a very promising non-thermal food processing technology, and it has become the hot spot of food industry recently. Currently most researches focused on the mechanism and kinetics of microbial inactivation, however, few researches related to the effects of PEF on enzymes, and the mechanism of enzyme inactivation under PEF is still unclear. Several hypotheses about the inactivation of enzyme were proposed but these hypotheses still has not been proved yet.PEF treatment was performed by using a laboratory scale pulse generator system (designed by Dalian University of Technology). The relative residual activity of commercial enzymes of horseradish peroxidase (POD) which is thermal resistance was investigated. The inactivation and conformational transitions of POD by PEF were studied systematically from theories and experiments. The change in tertiary structure of POD under PEF also was studied by computer molecular imitation. By doing so the enzyme inactivation kinetics studied previously was verified.1,The PEF-treatment system consisted of a square wave generator, a co-field tubular treatment chamber and a cooling system. The voltage, pulse duration and pulse frequency were available from 0 to 22 kV, 5 to 20μs and 10 to 1000Hz respectively.2,The activity of POD declined significantly after PEF treatment: the parameters in the experiment included square wave pulses of 17μs, electric field strength (0 kV/cm～20 kV/cm). The results showed that the inactivation of POD was significantly (P<0.01).And with the increasing of electric field strength, the inactivation effect of POD enhanced.The kinetic equation (?) may describe therelationship between electric field strength and relative activities of POD. The kinetic equation showed that the critical electric strength (E_c) of POD existed, which was 10.12±0.34 kV/cm. 3,Measured by size exclusion chromatography, the result showed that polypeptide chain of POD was not fractured by PEF treatment which meant the primary structure of POD did not change after PEF treatment.4,Measured by infrared spectrophometry the result showed that the secondary structure units of POD, including a-helix,β-strands, P-turn and random coil, presented nonmonotonic variation, with the increase of electric strength theβ-turn and random coil were transformed into a-helix andβ-strands.5,Measured by spectrofluorimetry, the result showed that the fluorescence intensity of POD declined in different degree after being treated by pulsed electric fields. And then it led to local variations on tertiary structure of POD. The higher the electric field intensity, the more obvious the effect is. The result also showed that just as in the process of inactivation, there was a same critical electric strength (E_c) during the fluorescence quenching which meant the relationship between the tertiary structure variation and the inactivation of POD was close.6,Computer molecular imitation vividly verified and showed that the whole molecular structure of POD did not change, but part of the groups of POD changed under PEF treatments.