Studies related to the degradation of food colouring matters
A differential pulse polarographic method has been developed for the determination of ascorbic acid and food colours in the same solution. Aniline, sulphanilic acid and naphthionic acid were shown to be formed from particular food colours: visible spectrophotometric methods involving diazotization and coupling with N-l-naphthylethylenediamine dihydrochloride.were developed for monitoring their formation. The method is not subject to interference from the other amines formed from the cleavage of the azo bonds. Ammonia was shown to be present in the degraded solution and an indophenol method was developed for following its formation. These methods have been used to monitor permitted food colouring matters and ascorbic acid during interaction in accelerated light and heat degradation studies in the presence and absence of EOTA. Heat degradation studies were also carried out in the absence of ascorbic acid. EOTA was found not only to stabilise ascorbic acid but also to stabilise food colouring matters in the presence of ascorbic acid. Full yields of ammonia were obtained from the degradation of azo groups via sulphanilic acid and naphthionic acid during the light degradation studies. Interaction of food colours and ascorbic acid has also been shown to occur at room temperature in the dark and to yield ammonia and simple amines. In the heat degradation studies (130°C) relatively low yields of amines and ammonia were obtained despite complete visible degradation of food colours. This indicated the formation of more complex nitrogen containing compounds. EOTA was shown to stabilise acetamido groups from photolytic hydrolysis in several drug compounds as well as in the food colouring matters Red 2G and Black PN. A rapid differential pulse polarographic method for the determination of food colours in boiled sweets directly without prior separation or extraction procedures has been developed. A detector cell designed and constructed in our workshops and previously used with a glassy carbon electrode has been adapted very successfully for use with a sessile mercury drop electrode. The use of the system in flow injection analysis has been demonstrated by determining food colours in the reductive and oxidative modes. Ascorbic acid, sulphite and other species have also been determined. In the determination of ascorbic acid deoxygenation is not necessary.