Abstract
Chlorophyll plays a fundamental role in plants and fruits, and its disappearance is typically associated with senescence due to the autumnal leaf coloring. Chlorophyll breakdown, however, is not limited to senescence: fruits change color during ripening and early leaf yellowing or chlorosis is a well-studied symptom of biotic and abiotic stress. Recent work on apple (Malus domestica Borkh.) and other species has shown that chlorophyll is broken down to the same class of metabolites (phyllobilins), PBs, like the non-fluorescent chlorophyll catabolites, NCCs) via a common metabolic pathway mediated by pheophorbide a oxygenase (PaO) in all three cases: senescence, ripening and stress. Physiological roles for PBs have been proposed based on their antioxidative properties, and health benefits have been deduced from pharmacological activities, including anti-inflammatory properties and inhibiting activities against cancer cells. To gain a deeper understanding of the breakdown of chlorophyll in fruit species beyond the autumnal leaf yellowing, the abundance and diversity of PBs in ripe apples were investigated for the first time using ultra-high pressure liquid chromatography-high resolution quadrupole-time of flight-mass spectrometry (UHPLC-Q-TOF-MS) together with an inclusion list with 51 PBs. Ten chlorophyll catabolites, including five NCCs, one YCC, and four DNCCs (including a previously unknown one) were described for the first time in apples fruits.