MANILA, Philippines?The colors of products in sunlit display windows tend to fade faster compared to the items inside the store, making them look older than they actually are. Blame it on the heat and light that can unexpectedly age an item.

On supermarket shelves, a similar reaction has been noted in colorful beverages stored in bottles of varying shapes, colors and sizes. Beers and wines, for example, are among the beverages that are light-sensitive, which is why they?re bottled in colored glass. Still, not all light-sensitive food and drink are packaged the same way.

Sometimes products are kept in clear containers that expose them to light for design and marketing reasons. But temperature changes and the constant light from ceiling fixtures can change a drink?s flavor ahead of the labeled expiration date, especially if the product has been on the supermarket shelf for too long.

A better way

In the current issue of the Journal of Agricultural and Food Chemistry, Italian food scientists from the University of Udine describe a better way to predict how long a bottled drink could safely stay on the shelf without affecting flavor and color.

By means of a calculation that factors in room temperature and light levels, lead author Lara Manzocco and her colleagues say they can estimate a bottled liquid?s actual shelf life without conducting a taste test or relying on an expiration date.

To perfect their method, the researchers used a solution made of saffron powder mixed into water and stored in a test tube to simulate a bottled light-sensitive soft drink. The samples were then placed a few inches away from fluorescent lights, as if simulating direct sunlight. Manzocco and her colleagues then conducted a series of tests using the saffron-colored soft drink to find out how long it would take to lighten the solution?s color, indicating a negative change in product quality.

Sets of experiments

One set of experiments involved timing how long it took the color to change if the samples were kept under a constant light level while the temperatures were being steadily raised from 20 to 40 degrees Celsius, and then repeating the same test on samples kept in darkness.

In another set of experiments Manzocco and her colleagues kept the samples at a steady temperature (20 degrees Celsius, for example) but changed the light levels. From this they learned that it was light more than temperature that affected the color and thus the quality of the pretend soft drink.

Based on all the information, they came up with a mathematical formula that could one day be used to calculate an approximate shelf life for products in supermarkets and other similar outlets. The researchers also think the calculation could be used for fresh and frozen foods, whose shelf lives can?t be tested easily by checking their temperatures.

?The results obtained clearly show that shelf-life testing of light-sensitive foods must take into proper account the effect of light,? Manzocco and her colleagues wrote in the conclusion of their report. ?For photosensitive products, light was demonstrated to be a useful unconventional accelerating factor.?

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E-mail the author at massie@massie.com.