Changes in the activities of pro- and anti-oxidant enzymes in peach fruit inoculated with Cryptococcus laurentii or Penicillium expansum at 0 or 20 °C

Peach fruit (Amygdalus persica cv. Okubao) were inoculated with either antagonist Cryptococcus laurentii or pathogen Penicillium expansum and stored at 20 and 0 °C to investigate the effect of antagonist and pathogen on some pro- and anti-oxidant enzymes in non-infected flesh of fruit during storage. Both C. laurentii and P. expansum markedly induced activities of polyphenol oxidase (PPO), peroxidase (POD) and superoxide dismutase (SOD) in peach fruit at 20 °C, whereas only P. expansum had a significant effect on the inducing of malondialdehyde (MDA) content of the fruit. C. laurentii showed more efficiency in the promotion of PPO, POD and SOD activities of peach fruit than P. expansum. At 0 °C the inducing effect on the pro- and anti-oxidant enzymes by the yeast and pathogen was complex. The results indicated that both C. laurentii and P. expansum could induce anti-oxidant enzyme synthesis at 20 and 0 °C, but the rate of induction depended on storage temperature, inoculation time and treatment. PPO might play a key role in the defence system at both temperatures.