Page last updated at 19:37 GMT, Saturday, 15 August 2009 20:37 UK

Sub-zero proteins transform dessert

By Victoria Gill
Science reporter, BBC News

Ice cream cone
Do Antarctic fish hold the key to stopping your ice cream from dripping?

"You might remember, when you were a child, being able to suck out the fruity goodies from an ice pop, leaving just the colourless, flavourless ice behind," says Jim Crilly.

"With this new ingredient, you can't do that."

Dr Crilly is head of research at multi-national corporation Unilever's ice foods centre in Colworth.

He spent 17 years in ice cream research before becoming taking up his present post.

Dr Crilly is particularly excited about this new ingredient, which he calls "the biggest development in ice cream technology in 40 years".

The ingredient is a protein that controls the growth of ice crystals. "It allows us to use ice in an entirely new way," says Dr Crilly.

Ice structuring proteins have a long and very cold scientific history. The first ones were discovered in 1969 in the blood of Antarctic fish.

In polar regions, seawater temperatures can dip below 0C - at which point less saline liquids, such as the blood of fish, should freeze. Yet this does not happen, and scientists wondered how the fish were able to swim contentedly in those icy waters.

Nature created this - we just discovered that it had a practical use
Jim Crilly, Unilever

In his quest to find out, US animal biologist Arthur DeVries, examined their blood - looking for what might be different about these cold water survivors.

What he found was a protein that seemed to prevent ice crystals from growing.

As studies of these intriguing "anti-freeze" proteins progressed, they were discovered in many more organisms - fish, insects, bacteria, fungi and plants that have to survive freezing temperatures.

Many of our more hardy frost-surviving vegetables and even our humble lawns produce these ice structuring proteins when there is a harsh frost.

"In fact, when we were investigating them, we mowed the grass here at the research centre on a very cold day to extract the proteins," Dr Crilly recalls.

"Nature created this - we just discovered that it had a practical use."

Antarctic ice cream

For 15 years, Dr Crilly and his team have been studying and developing what are now referred to as ice structuring proteins. As well as stopping the ice in its tracks, these proteins can be used to grow it into a kind of bespoke pattern of ice crystals.

Eel pout fish
Biologists puzzled over how fish survived in icy waters

Unilever is now licensed to add them to ice creams and ice lollies.

The company is manufacturing one specific type of protein, based on one that was originally found in eel pout - a fish native to the North-West Atlantic.

But there are many types of ice structuring protein - that evolved in different organisms - which have to survive in their own specific environment.

Each one changes the ice in a slightly different way - by preventing the crystals from growing in a particular direction.

"You can produce unusual shaped ice crystals with these proteins and interesting properties of the ice itself," says Dr Crilly.

"You can have spicular, spherical and even rhomboid-shaped ice crystals."

"The one we're using inhibits growth in the lateral direction," explains Dr Crilly. This means the ice crystals cannot expand to grow fatter, but can get longer.

"It leads to ice particles of spicular (or needle-like) shape," he says.

These spiny ice crystals form a sort of scaffold, creating stable, non-drippy and slow-melting ice cream.

Stability is everything

It is all down to microstructure. Ice cream consists of ice crystals, air cells, fat droplets and a matrix - of water, sugars, fat and milk protein - that glues it all together.

Iced lollies
Protein scaffolds keep all the "goodies" locked into your iced lolly

It is very thermodynamically unstable, so it has to be kept cold, and it starts to deteriorate as soon as it is made.

"As the air cells 'coarse' and merge together, the ice cream collapses like a soufflé," says Dr Crilly. At the same time, ice crystals grow, leading to that hard lump of ice cream peppered with crunchy ice crystals you often find in the bottom of your freezer.

"Everyone knows the best ice cream comes straight from the factory line," says Dr Crilly. "But this (protein scaffold) can stop that coarsening and make the ice more stable."

And how do they stop you from sucking all the flavour out of an ice pop?

All the other ingredients are locked inside this continuous spiny scaffold, with no pockets of flavour and clumps of ice that you would have found if you had looked at your traditional ice pop under a microscope.

Dessert meets medicine

But there is a more serious side to these proteins.

According to Ido Braslavsky, a researcher from Ohio University in the US, who has spent more than a decade studying ice, the proteins could also find important medical applications.

Ice crystals
Fluorescent microscopy revealed how the tiny proteins bound to ice crystals

Dr Braslavsky is currently trying to find out exactly how ice structuring proteins work, and which ones could be tailored for medical use.

"When I heard about (these) proteins, I was very intrigued, because I was looking at how ice grows, and here were additives that you could use to manipulate it."

"I had the idea of studying these proteins using fluorescent microscopy," he says.

With the help of Professor Peter Davies from Queens University in Kingston, Canada, Dr Braslavsky has been able to attach fluorescent dye to the proteins, to look directly at how they interact with ice crystals.

"They stick to the surface of the ice crystal," explains Professor Braslavsky.

"There is very good match between the shape of the protein and the ice crystal (it binds to)."

Exactly how the proteins then go on to influence ice crystal growth is still not fully understood, but Professor Braslavsky has already started to look more closely at the interactions between the atoms of the protein and those of the ice crystal.

Through his fluorescent labelling studies, he is trying to find out why some ice structuring proteins are more active than others, and he thinks these "hyperactive" proteins could prove medically useful.

"The hyperactive ones bind to more surfaces and are able to prevent the ice from growing in (any) direction," he explains.

These proteins are found mainly in dry-land-dwelling bacteria and insects. "In terms of evolution, terrestrial organisms need to cope with colder temperatures than those that fish need to deal with," explains Professor Braslavsky.

"Salty water in the ocean doesn't get colder than about -2C, while the air in winter can drop to much colder that this."

He thinks it is these natural anti-freeze proteins that will eventually be used to protect human organs - transported on ice for transplantation - from deterioration.

Donor organ being transported
The "hyperactive" proteins could protect donor organs from damage

Currently, organs have to be transported at or just above 0C and are only viable outside of a body for a few hours. With these proteins, medical scientists hope that they could be kept at lower temperatures without being damaged by ice.

Other research teams are also testing the proteins' potential role in "cryomedicine" - for example, driving ice formation in a particular direction to freeze and destroy a tumour in the skin, whilst minimising damage to surrounding tissue.

Fermenting anti-freeze

Up until now, the fact that ice structuring proteins fulfil their role so efficiently has actually proved to be an obstacle for the scientists hoping to use them.

"When we were first studying them we tried to extract them from vegetables," says Dr Crilly.

"But they're produced in such tiny amounts that you would have to plant the whole of Wales with carrots in order to extract about 100g of the proteins."

So the company has developed a protein manufacturing process based on fermentation.

"We produce it with bakers' yeast, genetically modified to include the DNA extracted from fish," explains Dr Crilly.

This is a process used commonly in food production - to produce vitamins' flavourings, enzymes and vegetarian cheese.

"We also engineered the yeast cells so that the protein can break through the cell wall," explains Dr Crilly. The fermented yeast produces the protein, which is then micro-filtered and purified.

The result is a relatively cheap and easy way to produce large quantities of the proteins.

And Professor Braslavsky thinks that the ice cream revolution - and more specifically the availability of ice structuring proteins in large amounts - could have a positive impact on the other avenues of research into "ice control".

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