Tuesday, December 06, 2022

Grainy ice cream is unpleasant. Plant-based nanocrystals can help

You can never have too much ice cream, but you can have too much ice cream in your ice cream. The addition of plant-based nanocrystals to the frozen delicacy could help solve that problem, researchers reported at the American Chemical Society spring meeting in San Diego on March 20.

Ice cream contains small ice crystals that become larger when natural temperature fluctuations in the freezer cause them to melt and recrystallize. Stabilizers in ice cream – typically guar gum or locust bean gum – help inhibit crystal growth, but do not stop it completely. And as soon as ice crystals hit 50 micrometers in diameter, ice cream acquires an unpleasant, coarse, grainy texture.

Cellulose nanocrystals, or CNCs, obtained from wood pulp, have properties similar to gum, says Tao Wu, a food scientist at the University of Tennessee at Knoxville. They also share similarities with freezer proteins, which are produced by some animals to help them survive temperatures below freezing. Antifreeze proteins work by binding to the surface of ice crystals, which inhibit growth more effectively than gums – but they are also extremely expensive. CNCs may work similarly to freeze-free proteins, but at a fraction of the cost, Wu and his colleagues thought.

An experiment with a sucrose solution – a simplified ice cream instant server – and CNCs showed that the ice crystals stopped growing completely after 24 hours. A week later, the ice crystals remained at 25 micrometers, well below the threshold of ice crystals cracking. In a similar experiment with guar gum, ice crystals grew to 50 micrometers in just three days.

Microscope Images Of Large Ice Crystal Growth Compared To Small Ice Crystal Growth
Researchers have frozen a sucrose solution to see if cellulose nanocrystals, or CNCs, have slowed ice crystal growth. After a week, ice crystals in the solution with CNCs (right) did not grow as large as ice crystals in the solution without CNCs (left).Min Li

“This in itself suggests that nanocrystals are much more potent than gum,” said Richard Hartel, a food engineer at the University of Wisconsin-Madison who was not involved in the research. If CNCs do function in the same way as antifreeze proteins, they are a promising alternative to current stabilizers, he says. But this has yet to be proven.

Until that happens, you still have a good excuse to eat your ice cream quickly: You still would not want large ice crystals to form.

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