Further differential-pulse polarographic and visible spectrophotometric studies of the degradation of permitted synthetic food colouring matters with and without the addition of ascorbic acid: degradation in the dark and in the light without the stabilising action of EDTA

Abstract

In general, solutions of food colouring matters have been shown by differential-pulse polarography and visible spectrophotometry to degrade faster under accelerated light degradation conditions at pH 5.5 in the presence of asorbic acid when EDTA is absent. A full yield of ammonia from azo nitrogen atoms is obtained, and for Red 2G and Black PN the acetamido nitrogen atoms are also converted into ammonia in the absence of EDTA.

Degradation of food colouring matters in the dark in the presence of ascorbic acid, but in the absence of EDTA, has been shown to occur extensively over a period of several days. The relatively high concentration of ascorbic acid used degraded in a time similar to that required for the disappearance of colour of the food colouring matters and for this reason the simple amines formed, particularly naphthionic acid, remained in appreciable yield. Red 2G was observed to degrade by deacetylation to Red 10B, which is relatively stable to attack by ascorbic acid. Black PN also was observed to degrade initially to a coloured product, which could be either the deacetylated derivative of Black PN or a monoazo compound.

Ascorbic acid solutions stored in the dark became yellow and the unidentified product gave a polarographic reduction wave at -0.90 V (versus S.C.E.) at pH 5.5.