Abstract:

The aim of this study was to investigate how combined treatment with Pichia membranefaciens and chitosan
could affect defensive enzymes and substances in citrus fruits. The changes of defensive enzymes and substances during 7
and 28 days of storage were examined by inoculating or dipping citrus fruits with Pichia membranefaciens combined with
chitosan respectively. The results were reported as follows: compared with the control group, the activities of the defensive
enzymes phenylalanine ammonialyase (PAL), peroxidase (POD), polyphenoloxidase (PPO), chitinase, and β-1,3 glucanase
in citrus fruits inoculated with Pichia membranefaciens in combination with chitosan were increased significantly during
storage. PAL, POD, and β-1,3 glucanase were most evidently increased and reached the maximum on day 3. On the other
hand, the activities of PAL, POD and chitinase and lignin content were increased significantly and reached the maximum on
day 14 in citrus fruits dipped with Pichia membranefaciens in combination with chitosan. In conclusion, disease resistance in
citrus fruits can be enhanced by Pichia membranefaciens combined with chitosan through inducing an increase in defensive
enzymes and substances such as phenolics and lignin. Defensive enzymes and substances play a major role in disease
resistance in the early and late stages of storage, respectively.

Key words: induced defense responses, defensive enzymes, defensive substances, citrus fruit