The influence of crop maturity and ethylene on postharvest browning in celery

Celery (Apium graveolens L.) is a leafy vegetable which is commonly eaten raw and appreciated by consumers for the bright green and fresh petioles. Cut-end browning is one of the most relevant postharvest “disorders” negatively affecting visual quality and it renders products unmarketable. Cut-end browning is thought to be due to the enzymatic activity of polyphenol oxidases (PPOs) which oxidase phenolic compounds to produce dark pigments on damaged tissues. Given the relevance of this postharvest problem, in the present study we investigated the influence of crop developmental stage and the plant hormone ethylene on cut-end browning in celery. The experiment was replicated across two growing seasons; early and late. The crop reached commercial maturity 19 and 12 weeks after planting respectively. The cultivar 'Monterey' was used and grown in Spain (Murcia). In each replicate trial, celery heads were trimmed every week to obtain immature, commercially mature and over-mature plants. After harvest, samples were divided into two batches to run two experiments in parallel. The first batch was stored at 20°C temperature and 55.5% relative humidity and the second was further divided into three sub-batches for postharvest treatments (continuous air, continuous ethylene and continuous air after 1-methylcyclopropene treatment) at 5°C temperature and 95% relative humidity. During the storage period (12 days) samples were periodically assessed for subjective and objective colour at both apical petiole and butt ends surfaces. Results showed that browning developed over storage in general and intensified as crop maturity increased. Conversely, ethylene did not have any significant effect on cut-end discolouration. In conclusion, findings suggest that cut-end browning seems to be more prevalent in later stages of crop maturity, whilst ethylene does not seem to be involved in its underlying mechanism.