Quinone-mediated non-enzymatic browning in model systems during long-term storage

Non-enzymatic browning induced by polyphenol oxidation is an essential problem during the processing and storage of fruit and vegetable products. Here, the non-enzymatic browning mechanism between catechin (CAT), chlorogenic acid (CQA) and their corresponding quinones was investigated in model systems during the 32-d long-term storage. The results showed that CAT and catechin quinone (CATQ), which contains both A ring with a resorcinol structure and an o-diphenol B ring, are important precursors for browning, while chlorogenic acid (CQA) has a minor effect on browning. Chlorogenic acid quinone (CQAQ)-mediated CAT oxidation (k_{CAT-degradation} = 0.0458 mol·L^-1·d^-1) was faster than CAT autoxidation (k_{CAT-degradation} = 0.0006 mol·L^-1·d^-1), and there was no significant difference between CQAQ-mediated CAT oxidation and CATQ-mediated CQA oxidation. These indicate that CQAQ oxidizes CAT to CATQ quickly, and CATQ reacts with CAT subsequently through complex reactions to produce brown pigments in model systems during long-term storage.