Meat Iridescence ~ Corned beef pictured by John Flyte Jr of Pennsylvania.    Although of repulsive appearance, the colours are solely due to optical interference effects and the meat is as edible as that without colours.   Iridescence particularly afflicts sliced meats - Some sliced pork pictured by Steven Boersma is below.

Images ©John Flyte Jr & ©Steven Boersma. Shown with permission

Meat iridescence colours are a known issue.    They occur on raw meat but are perhaps more common on smooth surfaced cooked/cured meats.   They depend on the lighting angle. They could depend on the cutting blade and meat moisture content. Unpleasant greens are common, also reds and pinks.

Animal muscle is composed of quasi regularly spaced and oriented bundles of individual fibres.   In turn, the fibres contain long oriented myofibrils also regularly positioned.   When meat is sliced the fibres and fibrils can partly protrude from the surface to form a two-dimensional stepped array that forms a diffraction grating.   Microfibrils at cut fibre ends can also act as quasi-periodic scattering areas.

Light waves scattered by the regularly spaced protrusions and microfibrils constructively interfere and send coloured light in particular directions.

Birefringence could also contribute.

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Bright green, gold and pink iridescence in sliced pork. Image by Steven Boersma. Thanks also to Steven Boersma for alerting OPOD to the topic and for further reading references (1,2,3).