Study On Inactivation Kinetics Of POD & PG In Pulsed Electric Fields

Pulsed eletric fields (PEF) is one of the most promising technologies in the fieldof non-thermal food processing, which can maintain the original quality of the food ina great degree.In respect of the use of PEF as preservation technology, its impact on foodquality degrading enzymes is of particular interest.PEF treatment was performed using a laboratory scale pulse generator system(designed by Dalian University of Technology). The relative residual activities ofcommercial enzymes of horseradish peroxidase (POD) and polygalacturonase (PG)which are thermal resistance were investigated with PEF treatments in water andNa-acetate buffers solution respectively. The relationship between PEF electricintensities, treatments time and the relative residual activities of POD and PG werediscussed respectively, then the mathmetical models were built.1．This paper confirmed PEF belonging to non-thermal category ofpasteurization without thermal effect. The results showed that under the strongestprocessing condition in the experiments, the range of elevated temperature was lessthan 30℃which mean that PEF is non-thermal technology.2．The activities of POD was inhibited immediately with PEF treatment: theparameters in the experiment included square wave pulses of 17μs, differences inelectric field strength (10 kV/cm～20 kV/cm) and numbers of pulses (up to 110) . Theresults showed that the inactivation of POD was significantly (P<0．01) . The residualrelative activities of POD in water (pH=6．4) and Na-acetate buffer (pH=5．6) solutionswith PEF treatment at 20 kV/cm required 80 and 110 pulses, decreased to 1．98% and33．5% respectively.3．The activities of PG was inhibited immediately with PEF treatments: theparameters in the experiment included square wave pulses of 17μs, differences inelectric field strength (10 kV/cm～20 kV/cm) and numbers of pulses (up to 270) . Theresults showed that inactivation of PG was significantly (P<0．01) . The residualrelative activities of PG in water (pH=5．9) and Na-acetate buffer (pH=4．0) solutions with PEF treatment at 20 kV/cm required 270 pulses, decreased to 0．14% and 31．2%respectively.4．The first-order kinetic model ,RA＝e^-K_ε-1 , may describe the relationshipsbetween PEF treatment time and relative activities of POD & PG, and R²>0．98R²>0．93, respectively.The critical electric stength (E_c) of POD in water and Na-acetate buffer solutionsare 0．019±0．0035 kV/cm and 10．12±0．34 kV/cm, respectively. And E_c of PG in wateris 9．11±0．24 kV/cm, and 10．05±0．46 kV/cm it's when soluted in Na-acetate buffer.5．The relationship of electric strength (E) and constant K_E could be described bythe K_E＝K₀₁·e^[ω·(E-E_c)], and the R²>0．98．6．The kinetic model of inhibition of POD and PG activities after PEF treatmentwas studied, RA＝e⁽-K₀₁·e^{[ω·(E-E_c)]}_-t, which may describe the changes of PODand PG relative activities with the coexistence of PEF electric strength and treatmenttime.7．PEF treatment can decrease the POD activity in carrot juice, the residualrelative activity is down to 85．24% when electric field strength and numbers of pulsesare 12．5kV/cm and 20, respectively.