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The intricate exoskeletons of lobsters, crabs, and shrimps are an immense untapped resource: several million tons of this seafood waste is dumped each year, when its abundant organic polymer, chitin, could instead be extracted to make biodegradable packaging, food, and even pharmaceutical and cosmetic additives.
While some have found a way to extract chitin from crustacean shells, that process requires corrosive industrial chemicals such as hydrochloric acid, which require high temperatures to work, are polluting to the environment, and need large amounts of water to neutralize their toxicity at end of life. But now, a team of researchers has found a greener alternative method to tap into this immense chitin reserve.
Their discovery takes the shape of a viscous solvent that can be applied to the crushed carapaces of shellfish to tease apart its dense multilayered network of chitin, protein, and calcium salts. In the conventional process, hydrochloric acid and other synthetic ingredients are added to break apart hydrogen bonds in the material. That step is crucial for releasing the valuable chitin within. To get around the need for corrosive industrial acids in the mix, the researchers went on a hunt for alternatives that could achieve the same end while causing less harm.
Two possibilities that stood out were the organic lactic and malic acids, two ingredients found in commonly-consumed foods. They also selected glycerol, a “non-toxic, biocompatible, and cost-effective byproduct of the biodiesel industry”, they explain, and choline chloride, a salt that’s frequently used as a food additive. Both of the organic acids and glycerol are what’s known as hydrogen donors, meaning they will release some of their hydrogen atoms in the presence of ingredients such as choline chloride, which is a hydrogen acceptor.
With this in mind, the scientists tested out two three-ingredient recipes: glycerol, choline chloride, and either lactic acid or malic acid. These unique combinations each formed what the researchers describe as a solvent that was “rich in hydrogen bonds”. This rich hydrogen mix is important, because it essentially overpowers and shatters the original bonds in the shellfish material, from there enabling the separation and release of chitin from other compounds in the shell’s complex matrix.
To test out their new green solvents, the researchers bought grocery store snow crab legs and claws, boiled off the meat, and then baked the leftover shells at a high heat before crushing them into a fine powder. They applied mainly two types of solvent: one with glycerol, choline chloride and lactic acid, and another that replaced the lactic with malic acid.
While both mixtures managed to break hydrogen bonds and draw out the chitin, the one that really stood out was the mixture containing lactic acid. This one, the researchers found, remained effective at breaking down crab shells after three uses, making it the more efficient and sustainable choice. What’s more, unlike regular solvents this one didn’t require high temperatures to function, nor did it need vast amounts of water to neutralize its toxicity at end of life.
This makes it all the more promising for real-world applications. Of the estimated eight million tons produced annually, a huge chunk of those crab, lobster, and shrimp shells end up in waste dumps inland or at the coast, where they leach out excess nutrients just like any other type of organic waste, polluting the soil, freshwater, and marine ecosystems.
The benefit of the more eco-friendly process, therefore, isn’t only that it replaces harsher chemicals, but that its relative efficiency and cost-effectiveness might make it easier to transform more of those seafood waste streams into something useful.
Chitin has big potential as a biodegradable replacement for plastic packaging, but now the research team are now looking into another specific use: turning salvaged chitin into a nutrient-rich fertilizer for crops. “We are hoping that we can turn this trash into a treasure — or at least into value-added products,” they say.
Luo et. al. “Glycerol/organic acid-based ternary deep eutectic solvents as a green approach to recover chitin with different molecular weight from seafood waste.” International Journals of Biological Macromolecules. 2024.
Image: Wirot Pathi/Vecteezy
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