Citric acid and the browning of solutions containing ascorbic acid

Model systems were used to simulate lemon juice so that the findings may be applicable to the non‐enzymic browning phenomenon which occurs on storage of citrus juices. The addition of citric acid to systems containing ascorbic acid resulted in augmented chromophore development. Evidence is given to show that citric acid neither acts as a catalyst nor yields reactive carbonyl compounds under aerobic incubation conditions. Thin‐layer chromatographic separation of the brown pigments in different systems demonstrated a specific chromophore which occurred only when citric acid and ascorbic acid were both present. The presence of amino acids in ascorbic systems is the major contributor to the development of browning but it is suggested that citric acid, or a derivative, is incorporated into some of the brown pigments.