Peroxidase is one of the most heat resistant enzymes and may cause undesirable quality changes in thermally processed foods. Peroxidase activity and its resistance to thermal inactivation in fresh and pasteurized lump, claw and flake meat of both male and female blue crabs was determined spectrophotometrically. Activity was greatest in the flake and least in the claw. Male crabs usually exhibited a greater initial activity (λ 0D 460/min) than did females of equal size. The larger the crab for a given sex, the greater the initial activity.

Eight isozymes of peroxidase were detected in raw extracts of a 115 g female blue crab following starch gel electrophoresis and nine in a 116 g male. A smaller female crab (96 g) revealed seven bands which were less intense than those of larger females. By extending the time of electrophoresis, twelve bands were detected in the gel containing an extract from the 96 g female crab.

The optimum thermal processing times needed to denature peroxidase and to prevent regeneration were studied. Heat inactivation curves indicated two straight line decreasing segments which varied by rate of descent. The first segment which decreased at a faster rate was considered due to heat-labile isozymes and the second segment which decreased at a slower rate due to heat stable isozymes. D values obtained for the enzyme based on the second straight line segment were D80=47 min, D110=18.2 min and D150=11.2 min. A "z" value of 92 F was also obtained for the enzyme.