DISTRIBUTION AND HEAT INACTIVATION OF PEROXIDASE ISOENZYMES IN SWEET CORN

The distribution and heat inactivation of peroxidase (EC 1.11.1.7) isoenzymes in the pericarp, germ and endosperm of three sweet-corn ( Zea mays ) hybrids (Hawaiian hybrid H68, high-lysine hybrid o₂su COMP 1c, and a high-sucrose hybrid sh2 SYN 2e) were investigated. Polyacrylamide gel electrophoresis showed that the isoenzyme content of all three tissue fractions were complex with the pericarp having the largest number of isoenzymes. Isoenzyme distributions in the three varieties were similar but with exceptions, the most notable being the relatively simple distribution in the endosperm of H68. Studies on relative heat stabilities of the peroxidase isoenzymes at 71°C showed that no fraction was completely heat resistant although most bands did contain some heat resistant forms. Only one isoenzyme fraction, which was present in all three varieties, was completely heat labile. In contrast, some isoenzyme bands in the germ and endosperm were completely heat labile in some varieties but not in others. These results suggest that heat inactivation and consequently, residual peroxidatic activity found in processed corn is determined not only by isoenzyme content but also by the variable heat resistance of some isoenzyme fractions.