Effects of pulsed electric fields on the quality of foods

Papain, a cysteine protease in papaya, was chosen as a model enzyme for enzymatic inactivation by Pulsed Electric Fields (PEF). Irreversible reduction of activity was observed in PEF-treated papain after 24 hr storage at 4°C. Oxidation of papain active site, a cysteine residue, was not the major cause of papain inactivation by PER Temperature did not increase over 35°C during PEF treatment. The pH of papain solution was not changed after PEF treatment. Structural change was observed in PEF-treated papain by absorbance at 280 nm and CD analysis. Inactivation of papain by PEF was related to the loss of α-helix structure.;Orange juice was treated with PEF in a pilot plant system to optimize PEF processing conditions for maximum microbial inactivation and to investigate the effects of PEF on the pectin methyl esterase (PME) activity. Electric field strengths of 20, 25, 30 and 35 kV/cm and total treatment time of 39, 49 and 59 μs were used. The higher electric field strength and the longer total treatment time were the more effective to inactivate microorganisms and PME (p < 0.05). PEF treatment of orange juice at 3 5 kV/cm for 59 μs caused 7 log reduction in the total aerobic plate counts and the yeast and mold counts. About 90% of PME activity was inactivated by PEF treatment at 35 kV/cm for 59 μs.;Effects of PEF at 35 kV/cm for 59 μs on the quality of orange juice were investigated and compared with heat pasteurization at 94.6°C for 30 s. The PEF treatment prevented the growth of microorganisms at 4, 22 and 37°C for 112 days and inactivated about 90% of PME activity. The inactivated PME did not regenerate at 4 and 22°C for 112 days. The PEF treated orange juice retained more vitamin C and flavor compounds than the heat pasteurized orange juice during storage at 4°C (p < 0.05). The PEF treated orange juice had lower browning index, higher L value and lower a value than the heat pasteurized orange juice during storage at 4°C (p < 0.05). The PEF treated orange juice showed more stable cloud than the heat pasteurized orange juice that might be due to smaller particle size (p 0.05).