Submitted to: Postharvest Unlimited
Publication Type: Proceedings
Publication Acceptance Date: 7/21/2017
Publication Date: 10/17/2017
Citation: Mctavish, C.K., Torres, C., Mattheis, J.P., Rudell Jr, D.R. 2017. Metabolism characterizing sun exposed and shaded side peel of four apple cultivars during cold storage. Postharvest Unlimited. October 17, 2017, Madrid, Sprain.
Technical Abstract: Solar and heat stress can result in apple peel damage in the orchard and following harvest during cold storage. Sunburn can be apparent at harvest and worsen into a more brown or black color, called sunscald, during storage. In some cultivars, such as ‘Granny Smith’, sunscald can also develop entirely during storage on otherwise asymptomatic peel rendering fruit unexpectedly unmarketable. To date, the majority metabolic analyses associated with these disorders have focused on pathways associated with photoprotection within the chloroplast or phenolic compounds that ostensibly confer photoprotection. Our study used untargeted metabolic profiling to also examine changes outside these pathways including membrane, wax, and volatile components associated with processes during storage yet reflecting the general attitude with respect to the sun prior to harvest. The metabolome of sun-exposed and shaded peel of every cultivar was different at harvest and continued to differentiate during cold storage. As reported in earlier work, flavonol glycoside and chlorogenic acid levels were elevated on the sun exposed side. Examples within the volatile profile, where aldehyde production, particularly E-2-pentenal, were more prevalent in sun exposed peel and more varietal characteristic alcohols and esters on the shaded side. Epicuticular components derived from ursolic and oleanolic acid were also consistently different at harvest and continued to differentiate during storage. Results outline far more dramatic local differences based on sun exposure beyond the obvious visual differences and continued changes based on the dual stimuli of solar followed chilling stress. Changes that may reflect or be attributed to sunscald are indicated by potential roles of individual pathways.