Effect of Atmosphere Modification on Internal Physiological Browning of 'Fuerte' Avocados

Fuerte' avocados were stored under controlled atmosphere (CA), modified atmosphere (CO2 shock) and regular atmosphere (RA) conditions for 4 weeks. Prior to, during and after storage, fruit samples were analyzed for PPO activity and ABA-content. Both PPO activity and ABA content were lowest in CO2 shock-treated fruit which indicated that these fruit may have been subjected to lower post harvest stress than fruit from the other treatments. PPO activity was highest in ripe CA-treated fruit, but these fruit had the lowest incidence of physiological browning. The highest incidence of browning was found in RA- treated fruit. CO2 shock can extend the storage life and maintain the quality of avocados because it decreases the potential for postharvest disorder development and is relatively easy and cost effective to apply. South Africa is separated from its overseas markets by more than 9000 km and avocados exported to these markets can take up to 30 days to reach their destination, sometimes arriving in an advanced stage of maturity (Bower and Cutting, 1988). Lowering the shipping temperature to prevent this is not feasible due to the danger of chilling injury (Couey, 1982). In South Africa, it was shown that CA storage decreased the risk of chilling injury considerably (Truter and Eksteen, 1987). The optimum CA- conditions for avocados are 2% O2/10% CO2 at 5.5C (Hatton and Reeder, 1972; Truter and Eksteen, 1987). Internal physiological disorders may also be induced by low temperature storage (Engelbrecht and Koster, 1986). Eaks (1976) found that a period of longer than 14 days at a temperature of 5.5C increases the risk of physiological disorders. In order to land South African avocados in Europe in an unripe state, exporters are forced to use temperatures around 5.5C during the shipping phase.