PPO activity as well as PPO isoform distribution depended on ripeness
stage and part of the fruit. The highest PPO activity was found
in skin samples of very overripe Ataulfo. Samples with high PPO
activity displayed at least two PPO isoforms (53 and 112 or
144 kDa), whereas samples with low PPO activity showed only
one major band at 53 kDa in partially denaturing SDS–PAGE gels
stained for catecholase activity. The anionic detergent SDS was
an activator of PPO. SDS enhancement was notably stronger for
pulp compared to skin samples. The ripeness stage and the part
of the plant that was used for extract preparation should therefore
always be considered in the evaluation or comparison of enzymatic
browning reactions.
Acknowledgements
This research project was funded by a Faculty Support Grant
from California State University, East Bay. We thank Dr. Danika
LeDuc for carefully reading our manuscript.