Oxidation behaviour of vanillin in dairy products

The stability of vanillin in dairy products was investigated by means of highperformance liquid chromatography. While vanillin was oxidised to vanillic acid in fresh and pasteurised milk, it was stable in all other milk products investigated (UHT milk, pasteurised and UHT cream, yoghurt, curd and butter). The oxidation of vanillin to vanillic acid was shown to be pH-dependent. The relatively thermolabile enzyme xanthine oxidase was shown to be partly responsible for the formation of vanillic acid. However, peroxidase, which is also present in dairy products, did not lead to vanillic acid. Oxidation to the dimeric product, divanillin, occurred in the presence of peroxidase and hydrogen peroxide. The oxidation rate of synthetic vanillin to vanillic acid was very similar to that of vanillin from natural vanilla extracts or vanilla capsules. Both were shown to be stable in dairy products for subvention, such as butter and cream.