Submitted to: Phytochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2011
Publication Date: 6/2/2011
Citation: Rudell Jr, D.R., Buchanan, D.A., Leisso, R.S., Whitaker, B.D., Mattheis, J.P., Zhu, Y., Varanasi, V. 2011. Ripening, storage temperature, ethylene action, and oxidative stress alter apple peel phytosterol metabolism. Phytochemistry. 72:1328-1340. Interpretive Summary: Changes in the natural peel chemistry of apples precede the apple peel browning disorder, superficial scald that can significantly impact fresh fruit value of susceptible apple varieties. This report identifies important chemicals called phytosterols and natural derivatives of these chemicals. Storage conditions, including temperature and various commonly applied postharvest crop protectants impact both scald incidence and development in addition to changes in the amount of phytosterols and related natural peel chemicals. It was concluded that these peel components may have a role in protecting the fruit from chilling and oxidative injury at a cellular level as well as a potential use as a harbinger of postharvest stress and thereby a component of a postharvest management tool.
Technical Abstract: The chilling conditions of apple cold storage can provoke an economically significant necrotic peel disorder called superficial scald (scald) in susceptible cultivars. Disorder development can be reduced by inhibiting ethylene action or oxidative stress. We found previously that scald is preceded by a metabolomic shift that results in altered levels of various classes of triterpenoids, including metabolites with mass spectral features similar to ß-sitosterol. In this study, a key class of metabolites was identified. Changes in levels of acylated steryl glycosides (ASG), as well as steryl glycosides (SG) and steryl esters (SE) comprised of the free sterols (FS) ß-sitosterol and campesterol were evaluated during the period of scald development in response to pre-storage treatment with the ethylene action inhibitor 1-methylcyclopropene or an antioxidant (diphenylamine), rapid temperature elevation, and cold acclimation using intermittent warming treatments. Diphenylamine, 1-MCP, and intermittent warming all reduced or prevented scald development. ASG levels increased and SE levels decreased in untreated control fruit during storage. Removing fruit from cold storage to ambient temperature provoked rapid shifts in ASG and SE acyl moieties from unsaturated to saturated. FS and SG levels remained relatively stable during storage but SG levels increased following temperature increases after storage. ASG, SE, and SG levels did not increase during 6 months cold storage in fruit subjected to intermittent warming treatment. Overall, the results show that apple peel phytosteryl conjugate metabolism is influenced by storage duration, oxidative stress, ethylene action/ripening, and storage temperature.