Postharvest Biology and Technology 23 (2001) 33 – 39 Effect of high carbon dioxide concentration on PAL activity and phenolic contents in ripening cherimoya fruit Joston S. Assis 1 , Roberto Maldonado, Teresa Mun ˜ oz, Marı ´a I. Escribano, Carmen Merodio * Departamento de Ciencia y Tecnologı ´a de Productos Vegetales, Instituto del Frı ´o, Consejo Superior de Inestigaciones Cientı ´ficas, Ciudad Uniersitaria, 28040 -Madrid, Spain Received 20 September 2000; accepted 9 February 2001 Abstract Cherimoya fruit (Annona cherimola, Mill.) were kept at 20°C in air or in 20% CO 2 for 3 days and then transferred to air, to study the effect of a high CO 2 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°C was observed. The maximum ethylene production was observed 2 days later. At the end of the CO 2 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°C was not affected by high CO 2 and does not relate to ethylene. The CO 2 treatment inhibited flesh softening and maintained lignin at levels found in freshly harvested fruit. Exposure to 20% CO 2 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 CO 2 treatment at 20°C 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. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Cherimoya; Ambient temperature; High CO 2 levels; Lignification; PAL; Polyphenols www.elsevier.com/locate/postharvbio 1. Introduction The responses of fruit and vegetables to high CO 2 levels vary considerably among cultivars and spe- cies, and include both undesirable and beneficial physiological and biochemical changes (Beaudry, 1999). Moreover, it is well known that the effect of CO 2 depends on its dosage and environmental conditions such as temperature (Smith, 1992). * Corresponding author. Tel.: +34-91-5445607; fax: +34- 91-5493627. E-mail address: merodio@if.csic.es (C. Merodio). 1 Present address: Embrapa Semi-Arido, CP 23, CEP 56.300-000 Petrolina-Pernambuco-Brasil. 0925-5214/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0925-5214(01)00100-4