Carbonyl compounds and the non-enzymic browning of lemon juice

During the non‐enzymic browning of lemon juice the build‐up of carbonyl compounds is believed to be associated with the breakdown of ascorbic acid. This has been studied by separation of their 2,4‐dinitrophenylhydrazine derivatives on thin‐layer chromatograms, and by spectroscopic examinations. The results have been compared with those from model systems. Twelve carbonyls were found in browned samples, half of these have been tentatively identified and the remainder have been classified as aldehydes or ketones. Work with model systems confirmed that the α,β‐unsaturated carbonyls are potent browning agents and also that dicarbonyls of the glyoxal type make a contribution to browning in the early stages. The rǒle of sugars in these systems has been considered.