Relationship between flesh browning and the activities of polyphenol oxidase, peroxidase and phenylalanine ammonia-lyase in feijoa fruit

Abstract

Flesh browning is the main postharvest disorder limiting the storage life of feijoa fruit produced in southern Brazil. The aim of this study was to evaluate the relationship between the activity of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) and incidence of flesh browning in five Brazilian genotypes of feijoa: cultivars 'Alcântara', 'Helena', 'Mattos' and 'Nonante', and the access 2316. Fruit of all genotypes were harvested at commercial maturity in 2013, and cold stored for 7 and 14 days (4±1°C/90±5% RH), followed by 48 h of shelf life (23±1°C/75±5% RH). The activities of PPO, POD and PAL and incidence of fresh browning were assessed at the harvest and after 7 and 14 days of cold storage (followed by shelf life). On average of all genotypes, the activity of PPO increased 29% from harvest to 7 days of cold storage, and 37% from 7 to 14 days of cold storage. PPO activity after 14 days of cold storage was highest in 'Mattos' and lowest in 'Helena'. POD activity was low in all genotypes and decreased from harvest until 14 days of cold storage. In all genotypes, PAL activity did not change from harvest until 7 days of cold storage but increased from 7 to 14 days of cold storage (by 11-28%) in 'Alcântara', 'Helena' and 'access 2316'. 'Mattos' had the highest PAL activity, which did not change from harvest until 14 days of cold storage. The severity of pulp browning after 14 days of cold storage (followed by shelf life) was higher in 'Mattos', 'Alcântara' and 'access 2316', and lower in 'Nonante' and 'Helena'. The results show that the occurrence of flesh browning in the fruit of feijoa genotypes cultivated in southern Brazil is associated fruit senescence, and related to the increase of PPO and PAL activities during storage (especially of PPO). POD activity was low in all genotypes of feijoa and, therefore, the enzyme seems to have little effect on the internal browning.