Effect of high carbon dioxide concentration on PAL activity and phenolic contents in ripening cherimoya fruit

Cherimoya fruit (Annona cherimola, Mill.) were kept at 20 degreesC in air or in 20% CO2 for 3 days and then transferred to air, to study the effect of a high CO2 treatment on phenolic metabolism and ripening-related changes. Total polyphenol levels remained constant while a rapid decline in lignin content was observed in cherimoyas stored in air. However, a sharp increase in PAL activity up to the second day at 20 degreesC was observed. The maximum ethylene production was observed 2 days later. At the end of the CO2 treatment, ethylene production was inhibited and PAL activity was similar to that found in air-treated fruit. These data suggest that the increase in PAL activity at 20 degreesC was not affected by high CO2 and does not relate to ethylene. The CO2 treatment inhibited flesh softening and maintained lignin at levels found in freshly harvested fruit. Exposure to 20% CO2 also improved internal colour and increased the non-tannin polyphenol fraction, but prevented the decline in the tannin fraction otherwise observed upon ripening in air. We concluded that high CO2 treatment at 20 degreesC did not enhance PAL activity and lignin deposition although treated fruits retained more lignin after transfer to air. The possible involvement of PAL activity in the supply of important metabolic compounds for early events of ripening will be discussed. (C) 2001 Elsevier Science B.V. All rights reserved.