Nationalgeographic.co.id—Is “Jelly” It could one day replace the cube that has been cooling your drink. This reusable jelly traps water within its sponge-like structure. The water freezes but doesn’t escape. Researchers at the University of California, Davis, hope their innovations can open up new frontiers in food refrigeration technology.
Ice jelly is made of hydrogel “water gel”. Hydrogels sound technical. But you’ve probably eaten hydrogel before—Jell-O. You can even freeze the popular food. But there is a problem. Once thawed, it turns into goop (semi-liquid).
But not with jelly ice cubes. They can be frozen and thawed, again and again. They are also environmentally friendly. Reusing it can save water. Plus, the hydrogel is biodegradable. Unlike plastic freezer packs, at the end of their useful life, they won’t leave any long-lived plastic waste behind. They can even be composted. After about 10 uses, you can use these cubes to increase garden growth.
Finally, they can make frozen food storage cleaner. In fact, that’s where the “original idea started”, says Luxin Wang. He is a microbiologist on the UC Davis team. When regular ice melts, bacteria can hitch a ride in the water to other foods stored in the same place. In this way, “it can cross-contaminate,” Wang said. But the hydrogel will not turn liquid again. After use, it can even be rinsed clean with liquid bleach.
The team described its hydrogel ice cubes in a paper published on November 22. This research was published in ACS Sustainable Chemistry & Engineering.
Alternative cooler
Just like ordinary ice, the substance in this hydrogel cooler is water.
Ice absorbs heat, making objects around it cooler. Think of “cold” simply as the absence of heat. When you hold an ice cube, it feels like cold is moving into your hand from the ice. But that cool feeling really comes from the heat escaping your hands. When the ice absorbs enough heat, it melts. But in jelly ice cubes, Wang explains, the water is “trapped in a gel structure.”
The team compared the hydrogel’s ability to cool food—its “cooling efficiency”—to that of ordinary ice. First, they pack food samples into foam-insulated containers and cool the food with jelly or regular ice cubes. Sensors measure changes in food temperature. Regular ice works better, but not by much. For example, after 50 minutes, the temperature of an ice-cooled sample is 3.4º Celsius (38º Fahrenheit). The gel-cooled sample was 4.4 C (40 F).
They also tested the strength of the hydrogel. Its spongy structure is made mostly of a protein called gelatin (as in Jell-O). Hydrogels with higher gelatin percentages were stronger but exhibited lower cooling efficiency. Tests revealed that hydrogels with 10 percent gelatin showed the best balance between cooling and strength.
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During manufacture, jelly ice cubes can be shaped into any shape. And that’s what research, medical, and food companies are interested in.
“We got an email from the lab manager,” Wang said. “They said, ‘That’s cool. Maybe you can make it into this shape?’ And they sent us pictures.”
For example, a small ball shape can be used as a cold delivery material. Or maybe a hydrogel could be used to hold the test tube. When scientists need test tubes to keep them cold outside the freezer, they often put them in an ice bath. But perhaps, Wang said, the gel could instead be made into “a shape where we can put a test tube in it.”
Work in progress
The jelly ice cubes are not ready to launch yet. “This is a prototype,” said Wang. “As we move forward, there will be additional improvements.”
Price is probably one of the downsides. Compared to regular ice, “most gels won’t be cheaper,” says Wang. At least not at first. But the option to cut costs exists—as if it was reused over and over again, for example. The team is already working on it. Wang said a new study showed better gel stability due to the different types of connections made between proteins in the gel sponge structure.
Another problem may be the use of gelatin itself. It’s an animal product and some people, such as vegetarians, won’t eat gelatin, says Michael Hickner. He teaches materials science at Penn State University in University Park. With these cubes, he notes, “You can get gelatin in foods you don’t want.”
Polymer scientist Irina Savina at the University of Brighton in the UK also has concerns. “It might be good to have a refrigerant that doesn’t leak; I would agree with that.” But cleaning with bleach can be a problem, she says. You don’t want to get bleach in your food, but gelatin can absorb the bleach and release it when it touches your food. He had other concerns. “Gelatin itself is food for microbes.”
Vladimir Lozinsky is a polymer scientist at the Russian Academy of Sciences in Moscow. He echoed Savina’s point. “I’m afraid the thawed cubes could be a source of nutrition for the microbes,” he says — including those that could make you sick. Even without the melted water, the cubes may still be in direct contact with the food. And that, he continued, “could be a problem.”
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Hickner agrees there are problems to be solved. But he also envisions possibilities for future applications, such as “food innovation.”
Freezing food can affect its texture. Especially when it comes to something like meat, which is made of whole cells. “Freezing destroys cells by creating long, knife-like ice crystals,” said Hickner of Penn State. Finding ways to reduce the damage caused by the freezing process can open up new possibilities. And in this hydrogel study, “they used a polymer to control the size of the ice crystals. It makes all the difference,” he said. Using a gelatin hydrogel may be “a great eco-friendly way to do this without using any really exotic preservatives.”
The eco-friendly potential of the cube is a “big goal,” according to Wang. Hydrogels can promote a “circular economy,” he says. “When you use something, like these cubes, they can come back into the environment, with minimal footprint on Earth.”
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