Light and copper catalysed oxidized flavours in stored milk

Oxidized flavour results from milk lipid oxidization which, in practice, is catalysed by either light (Λ around 450 nm) or Cu. Damaging levels of Cu may be present naturally in some milks but are usually due to contamination. Of the two defects. light‐induced flavour is today the more important by far, especially where milk is exposed to light in containers that transmit the damaging wavelengths and are, in addition, highly permeable to O 2 . Thus, in the UK. sterilized milk in blow‐moulded polyethylene bottles is especially at risk. The level of O 2 required to produce the development of Cu‐induced oxidized flavour is negligible compared with that in milk saturated with air. In contrast, light‐induced oxidized flavour develops only after considerable O 2 uptake has occurred in the milk due to ascorbic acid and other oxidations. In sterile milks exposed to fluorescent light with only the dissolved O 2 present, oxidized flavour did not develop. It did. however, develop where there was an additional supply of O 2 during storage. from a headspace or through an O 2 ‐ ‐ permeable container.