Published by Communications and Public Affairs (519) 824-4120, Ext. 56982 or 53338
October 06, 2003
Light-blocking resin improves juice vitamin content, shelf life, researchers find
Plastic juice bottles that are enhanced with an ultraviolet light-blocking resin could help reduce degradation of colour and vitamin C by as much as half, researchers at the University of Guelph have determined.
When bottled juice is left in the sunlight, the sun’s ultraviolet (UV) rays can rob it of its colour and vitamin C. That’s because clear plastic juice containers are made of polyethylene terephthalate, which doesn’t block UV rays effectively. Now, food science professor Ian Britt, engineering professor Valerie Davidson and graduate student Karen Conrad say improving these containers with a resin called polyethylene naphthalate (PEN) can give consumers a healthier, longer-lasting product.
“Food packaging is central in delivering safe, nutritious foods to Canadian consumers,” Britt said. “This work is only part of a continuing effort at Guelph to develop a sound understanding of how packaging systems can be designed to protect sensitive food products.”
Typically, high temperatures cause juices to darken in colour. But the U of G researchers discovered that some juices are initially bleached by UV light. The intense rays also speed degradation, reducing product shelf life to as little as one-third of that found under commercial lighting and dark conditions.
For their study, the researchers bottled apple and orange juices in plastic blended without PEN and in plastic blended with PEN at levels of 0.25, one and four per cent. For seven months, they stored one group of the juices in dark, controlled-environment chambers, another group in commercial fluorescent lighting (conditions that are typical to retail outlets), and a third group in intense UV light conditions. They used a chemistry lab technique called high-performance liquid chromatography – which is used to separate mixtures and measure concentrations of their components – to detect the degradation of vitamin C. Colour degradation was measured in terms of lightening or darkening of juice colour using colour-detecting instruments.
The study showed that bottles with PEN provided greater protection against vitamin C and colour degradation in the tested juices, primarily under the UV storage conditions. “We were really surprised at how a small amount of PEN could have such a positive impact,” Conrad said. Further research will look at how other juices and sports drinks are affected by light conditions.
“This is just the beginning,” Davidson said. “The findings are interesting, but there are many things that are still unexplained,” including why certain synthetic dyes are more unstable in sunlight than others. Conrad added that some blue- and red-coloured sports drinks have been bleached under UV conditions to the point of becoming clear within two to four hours. “Now that we know PEN is efficient, the market potential is great for such a product,” she said.
Currently, there is no known industrial use of PEN-blended plastic juice bottles. While PEN is known for its resistance to high temperature and UV light, it’s a costly material to buy for use in plastics. Further studies will test new plastics with various PEN contents to find a balance between increased shelf life and affordability.
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