Could milk get ultraviolet treatment?

01 Jun 2011

AT A 3000-cow dairy farm near Ithaca, New York, Rodrigo Bicalho wrestles a 3-week-old calf onto a scale. The calf totters about; the scale reads 52 kilograms, a healthy weight. Bicalho makes a note. He is trying to find out what happens if he gives his calves milk that, instead of being pasteurised, is treated with ultraviolet light.

While pasteurisation of foodstuffs has led to dramatic declines in foodborne illnesses, including tuberculosis, it does not kill all pathogens and can destroy some of the nutrients in milk, such as proteins and vitamins.

That can be a problem when using colostrum, for example. This is the first milk a mammal produces for its offspring, and it provides vital immunoglobulins to prevent disease in the newborn. Pasteurisation denatures these proteins, rendering them useless, says Bicalho, a veterinary scientist at nearby Cornell University. His is the first study to look at whether UV-treated milk might provide a viable alternative.

Exposure to UV light does not kill pathogens, but it damages their DNA enough to prevent them from reproducing. Although the technique can be used to purify water, it is still fairly new technology and it is not yet clear how effectively it deals with viruses and protozoans such as Giardia. What's more, the technique relies on light reaching all parts of the liquid; that's easy with water, but tricky with liquids such as milk and juice because of their opacity and coloration.

To get around this problem, Bicalho is using a device called the Turbulator, made by SurePure of Zug, Switzerland. It consists of a series of grooved cylinders with UV lamps running down the centre and a space 1.5 millimetres wide in between, through which the milk is passed. The grooves create a turbulent flow, and this ensures that all of the milk is exposed to UV light as it travels through the pipes.

Replacing pasteurisation with UV treatment promises to both inactivate pathogens and preserve a food's beneficial properties. The technology also uses a fraction of the energy of heat treatment, and could knock out those microbes that are unaffected by, or even thrive on pasteurisation.

Back at the farm, Bicalho pours a batch of cow colostrum into the Turbulator. The calves will receive either pasteurised or UV-treated milk until they are weaned and their weight and general health will be monitored.

The ultimate aim of work like this is to find out whether UV treatment would be suitable for baby milk. If a new mother cannot produce breast milk the baby is often given donated colostrum, which is typically pasteurised and so loses some of its quality.

Wine, beer and fruit juices might also benefit from UV treatment. Grape juice, for example, is used as a sweetener in many foodstuffs. It is often contaminated with a yeast called Zygosaccharomyces bailii, which is unaffected by pasteurisation but might be inactivated by UV.

It is still early days, though. UV treatment for juices was approved by the US Food and Drug Administration many years ago, but pasteurisation is still by far the most widely used method. Some 98 per cent of juice sold in the US is pasteurised.

Catherine Donnelly, a food microbiologist at the University of Vermont in Burlington and colleagues have shown that UV treatment inactivates Escherichia coli in cider. SurePure's technique is promising, Donnelly says, but adds that milk contains more pathogens than juice or cider. Proving that UV treatment renders milk safe for consumption is the next big challenge, she says.

Wine under the lamps

Too much sulphite, a common preservative in wine, can make for an unappealing taste and for some people, like Neil Patterson, head winemaker at the Anthonij Rupert winery in Franschhoek, South Africa, it can even cause allergic reactions.

Legally, sulphites in wine can reach 200 parts per million. But by replacing the chemicals with UV treatment during fermentation, some Rupert wines have dropped to a quarter of that level.

Reducing sulphite content brings out a wine's natural fruitiness, Patterson says. It also expedites the maturation process, so UV-treated wines could hit the shelves faster than their sulphite-treated counterparts.

Source: Cornell University