Consumers like to see what they are buying and the supermarkets use special lighting in order to sell more. The price consumers must pay for being able to see the food is that products can be damaged by the light. Dairy products develop "off" smells and tastes, meat products become grey, products rich in oil and fat turn rancid and vitamins are broken down.
Damaging light gets through the packaging even with UV filter (left).
Light of damaging wavelength is released by fluorescent tubes in the shop (right).
There is a widely held belief that it is UV light that is most damaging to food products and for some foods this is true. But the visible light from normal fluorescent tubes in the supermarkets is just as damaging to foods as the small amount of UV light they produce.
Nofima Mat is working on identifying the important light sensitive substances in various food products. This knowledge will then be used to develop and document necessary requirements for packaging. Various forms of light barrier built into the packaging can reduce the quality impairment of food.
Link to testing of light
Light and dairy products
Using fluorescence spectroscopy, sensory analyses and advanced data analysis, researchers at Nofima Mat have found that there are at least five light sensitive substances in dairy products in addition to riboflavin. These are chlorophyll a and b, protoporphyrin, hematoporphyrin and substances that contain chlorine. These substances appear to contribute significantly more to photo-oxidation than riboflavin. The studies that have been carried out at Nofima Mat cover milk, ice cream, butter, low fat soured creamed, cream cheese and white cheese (Norvegia). The measurement method used is fluorescence spectroscopy. This method, which is extremely sensitive, can measure the initiation of photo-oxidation in dairy products.
Light and sliced meat
The pigments in meat products such as cooked ham (pure meat) and saveloy (meat mixture) are very sensitive to light when oxygen is present in the pack and can easily develop a grey colour. When the product is exposed to light, residual oxygen in the pack must be as low as <0.2% to avoid discolouration. The product can tolerate some oxygen in the pack if it is in the dark and can tolerate light if there is no oxygen present, but oxygen and light together create problems.
The fresh pink colour turns grey in a matter of 6-8 hours in the chill counter if sufficient oxygen and light affect the product. The problem of discoloured sliced meat products has increased in recent years, which has been largely caused by a change from vacuum packing to packing in modified atmospheres.
The problem of discoloured food due to oxygen and light is greatest in the Nordic countries, where transparent packaging solutions have been chosen. In southern parts of Europe there is much greater use of a lightproof upper film and a transparent underfilm, so that the consumer can turn the pack over to judge the appearance of the product.
