Abstract: The invention provides a process of decolorising annatto-containing whey or products produced therefrom, by oxidation with hydrogen peroxide, characterised in that the oxidation is carried out in the presence of a catalytic amount of an active peroxidase, in that the amount of hydrogen peroxide used is sufficient to effect the oxidation of the annatto and in that the time for which the peroxidase is exposed to a deactivating concentration of hydrogen peroxide is insufficient to permanently deactivate the peroxidase. The process is generally applicable to inter alia whey, demineralised whey, reconstituted whey powders, whey protein concentrates and reconstituted whey protein concentrate powders. It may be applied as a batch, semicontinuous or a continuous in line process.