Pectin based Maillard reaction products: Formation mechanism and fluorescence characteristics

Pectin-based MR fluorescent product (PCD) was prepared using green-renewable pectin and l-lysine under the hydrothermal condition, which was characterized by bright yellow scaly powder. The chemical structural analysis showed that α-1,4-glucoside bonds linked active carbonyl compounds produced by demethoxylation and decarboxylation reactions in pectin, further react with l-lysine to form PCD with a moderate amount of π-conjugated structure, CN, CN, pyridine ring and pyrrole ring structure, causing yellow fluorescence in solid-state and stable blue fluorescence in liquid-state. Importantly, the steric hindrance and structural rigidity caused by pectin-like reticulated structure, more crystalline surfaces and structural complexity made PCD a good optical performance including covert apparent color, higher fluorescence quantum yield, less susceptibility to aggregated fluorescence quenching, excellent photostability, higher ion resistance, better solvent stability and wider pH application range than glucose-based MR product (GCD). This is favorable in the future for its potential application in anti-counterfeiting, fluorescence-responsive film preparation and bio-imaging.