Enzyme reactions leading to avocado fruit mesocarp discoloration

Ethylene involvement in chilling injury symptoms of avocado during cold storage

“…On the other hand, continuous application of ethylene (4 ml l − 1 at 5°C) caused 100% pulp browning and the highest PPO activity. 'Fuerte' fruit easily develops mesocarp discoloration when exposed to oxygen, because the mesocarp contains high levels of phenols, as well as high PPO activity (Kahn, 1977;van Lelyveld and Bower, 1984). In previous work, we showed that low O 2 atmospheres or application of acetaldehyde at 17°C reduced CI symptoms in 'Fuerte' fruit and reduced browning of fruit mesocarp (Pesis et al, 1994(Pesis et al, , 1998.…”

“…Mesocarp discoloration in the form of brown pulp results from oxidation of o-diphenols to oquinones, by polyphenol oxidase (PPO), and these continue to oxidize to form brown melanin pigments (Kahn, 1976). Kahn (1977) demonstrated a relationship between degree of pulp darkening and PPO activity in various avocado cultivars, and a relationship has also been shown between pulp browning and phenol content (van Lelyveld and Bower, 1984).…”

“…Darkening of the mesocarp during cold storage is one of the chilling injury (CI) symptoms expressed in avocado fruit (Chaplin et al, 1982;Bower et al, 1989;Cutting et al, 1990), and browning of the pulp causes major export losses every year (van Lelyveld and Bower, 1984). Mesocarp discoloration in the form of brown pulp results from oxidation of o-diphenols to oquinones, by polyphenol oxidase (PPO), and these continue to oxidize to form brown melanin pigments (Kahn, 1976).…”

Avocado Fruit Development and Ripening Physiology

“…While an alteration in the normal atmosphere surrounding the fruit may have positive effects during storage as discussed in the section on fruit ripening, incorrect ratios of oxygen to carbon dioxide may result in physiological disorders. Van Lelyveld and Bower (1984) and Bower and Van Lelyveld (1985) found that restricted ventilation leading to oxygen depletion, particularly towards the end of a prolonged (30 days) low-temperature shipping period, caused enhanced PPO activities, both soluble as well as total, implying activation and release of the enzyme. Visible browning also occurred, which is in accordance with the earlier work of Spalding and Marousky (1981).…”

“…There are, however, many references in the literature to mesocarp discoloration (Van Lelyveld and Bower 1984) and chilling injury (Chaplin et al 1982) which Couey (1982) attributed to long periods of cold storage during the transport of avocado fruit.…”