Photostability study of natural high-potency sweetener monatin in a model beverage system and characterisation of the degradation products

Abstract

Photodegradation of the naturally occurring high-potency sweetener monatin was studied in a lemon–lime beverage model system under simulated conditions. Most of the monatin disappeared after treatment with the equivalent of four days of ultraviolet light exposure and resulted in the formation of a number of degradation products. These degradation products have been isolated and characterised in the present study. On the basis of these identified structures, a photodegradation pathway has been proposed suggesting that monatin gets oxidised on the indole C-2 position to result in 2-hydroxymonatin. It also undergoes decarboxylation resulting in a 4-oxopentanoic acid analog and a major rearrangement resulting in an isonicotinic acid analog. Monatin also degrades into 3-formylindole and indole-3-carboxylic acid. Besides these, a partial monatin dimer and a monatin lactone were identified as additional degradation products. Details of the isolation and characterisation are given.