PURIFICATION AND CHARACTERIZATION OF PEROXIDASE FROM FRESH-CUT ZIZANIA LATIFOLIA

Peroxidase (POD) from fresh-cut Zizania latifolia was purified using a combination of (NH4)2SO4 fractionation and anion exchange chromatography, resulting in one cationic (PODc) and two anionic fractions (PODa I and II). The cationic fraction, which accounted for 76% of recovered activity, was further purified by gel filtration. The POD activity was purified 61.51-fold with 9.32% recovery. The purified enzyme contains three POD isoenzymes (PODc13) as estimated by native polyacrylamide gel electrophoresis and showed molecular weights of 20.622.1 kDa on sodium dodecyl sulphate polyacrylamide gel electrophoresis. The optimum pH and temperature were 6.0 and 40C, respectively. The enzyme was stable in the pH range 4.07.0 while retained only 2.21% of the activity after 1 min at 60C. The Km for guaiacol and H2O2 were 10 mM and 0.15% (v/v), respectively. Influence of various chemicals on the enzyme activity were studied. These results provide a theoretical basis for inhibiting browning and lignification of fresh-cut Z. latifolia. PRACTICAL APPLICATIONS The marketing of packaged and refrigerated fresh-cut Zizania latifolia is a choice of increasing interest for vegetables processors. However, cut surface browning and tissue lignification in fresh-cut Z. latifolia are two major causes of loss in quality. It has been reported that peroxidase (POD) may be involved in enzymatic browning and lignification. This study investigated the purification and characterization of POD from fresh-cut Z. latifolia. Results showed that heat treatment and/or chemical dip (L-cysteine, N-acetyl-L-cysteine and ascorbic acid) might be suitable techniques for inhibiting browning and lignification of the fresh-cut Z. latifolia.