Crude polyphenol oxidase (PPO) was extracted from pawpaw (Asimina triloba)
fruit. The enzyme exhibited a maximum activity at pH 6.5–7.0 and 5–20 °C, and had
a maximum catalysis rate (Vmax) of 0.1363 s-1 and a reaction constant (Km) of 0.3266
M. It was almost completely inactivated when incubated at 80 °C for 10 min. Two
isoforms of PPO (MW 28.2 and 38.3 kDa) were identified by Sephadex gel filtration
chromatography and polyacrylamide gel electrophoresis. Both the concentration and
the total activity of the two isoforms differed (P < 0.05) between seven genotypes of
pawpaw tested. Thermal stability (92 °C, 1–5 min) and colorimetry (L* a* b*)
analyses showed significant variations between genotypes. Pawpaw fruit samples that
were briefly heated (1–2 min) had improved color storage stability due to PPO
inactivation. Moreover, antioxidants were extracted from the same seven genotypes of
pawpaw fruit. All genotypes demonstrated significant (P < 0.05) radical-scavenging
capability and inhibited lipid oxidation in a liposome system. Overall, these findings
suggested that PPO-induced browning during pawpaw fruit processing may be
minimized through controlling pH and temperature. All genotypes of the fruit also
proved to be a good source of antioxidants.