Internal browning in apples is a significant post-harvest disorder that affects the quality and marketability of fruit. This phenomenon is influenced by a variety of factors, including genetics, environmental conditions, and storage practices, and although there are numerous studies, currently there is limited understanding of how internal browning can be prevented routinely, or observed without the destruction of the apple.
This presentation will highlight the progress of how using un-targeted metabolomic analysis focusing on semipolar and nonpolar compounds in apple skin and flesh could provide a tool to identify apples with a predisposition of internal flesh browning during apple storage. Greater understanding of the changes in metabolomic pathways before the onset of the non-reversible appearance of melanin, may help identify which of the influence factors associated with internal browning is the main driver in a particular orchard or storage setting.
In our study we observed amongst other lipids, an increase of Galactolipids (MGDG (36:6), DGDG (36:6)) in flesh from apples at harvest, originating from orchards with a higher browning incidence post storage. This indicates differences in thylakoid membrane composition in chloroplasts, compared to apples unaffected by browning, possibly caused by differences in light exposure in the affected orchards. Increased levels of secondary metabolites especially procyanidins, and their precursor epicatechin have also been observed in the flesh of apples at harvest with a predisposition to browning after storage. Procyanidins have been suggested to hold UV protection functions, therefore further indicating that growing conditions such as exposure to sunlight varies between apple orchards, and mitigating strategies might need to be implemented in orchards with higher browning incidences.