A versatile type of farm animal is emerging: the larvae of soldier flies are already booming as an alternative to fishmeal in the animal feed industry. Researchers have now shown that the adult insects that have not been used so far also have eco-use potential. They extracted raw materials for the production of biodegradable plastics from the flies. Another highlight is that the corresponding waste products could in turn serve as a source of food for the insect larvae – the circle can therefore be closed, say the scientists.
Littered to the ends of the earth – as is well known, mankind is struggling with increasing plastic pollution. The common polymers have two problematic aspects: Crude oil is required for their production and they can hardly be degraded in nature. Plastics based on natural substances have therefore already been successfully developed as alternatives. The research team led by Karen Wooley from Texas A&M University in College Station is also dedicated to this task. They are now reporting on their apparently unusual approach at the conference of the American Chemical Society in San Francisco.
“For 20 years we have been developing methods to convert natural substances – such as glucose derived from sugar cane or wood – into degradable polymers for plastics that do not remain in the environment,” says Wooley. So far, however, one aspect of sustainability has left a lot to be desired: “These natural products are mostly obtained from resources that can also be used for the production of food, fuel or building materials,” explains the scientist. Her team was therefore on the lookout for a previously untapped resource with potential for the production of bioplastics. The researchers came across a by-product of a currently booming industry that already serves sustainability: the breeding of soldier fly larvae.
Chitin from unused insect carcasses
The little “worms” are increasingly being used as a substitute for the ecologically more disadvantageous fishmeal in the feed industry – especially in the booming aquaculture of fish and in poultry farming. Various waste materials are suitable as food for the larvae. In order to provide for the offspring, however, significant numbers of adult insects must also mature in the breeding farms. After mating and laying eggs, however, these flies die quickly and are not suitable for food production. These enormous amounts of waste from fly carcasses were now the focus of Wooley and her colleagues. “We wanted to explore the possibility of making something useful out of this particular piece of junk,” says co-author Cassidy Tibbetts.
The team reports that the flies turned out to be a rich source of an already well-known sugar-based bio-polymer: chitin, which provides stability to the exoskeletons of insects and crustaceans. The researchers succeeded in extracting and purifying chitin from the insect carcasses using a series of adapted biochemical processes. In principle, this is not new – the substance has so far been obtained primarily from shrimp and crab shells and used for various purposes. According to the researchers, however, the flies can be used to extract high-quality chitin powder that lacks the yellowish color and lumpy texture of traditional products. It also eliminates the potential problem of seafood allergies. Insect chitin has been obtained before, but from larvae, the researchers emphasize. However, they have now utilized the adult fly’s throw-away element.
Applications that close circles
They have already implemented the substance in a sample application: To do this, the biochemists first converted the fly chitin into the polymer chitosan by splitting off the acetyl groups. This version has chemically reactive amino groups that can be activated and crosslinked. In this way, chitosan can be transformed into numerous useful bioplastics. To demonstrate, the team used fly chitosan to create a superabsorbent hydrogel that can absorb 47 times its weight in water in just one minute. This material can absorb excess moisture in the soil, for example, and release it to crops when needed. Because it is biodegradable, its molecular components can then gradually benefit soil fertility, the scientists say.
They now want to further explore the potential of the soldier flies as a source of raw materials and also work on processes for splitting the chitin into usable building blocks. Ultimately, Wooley and her colleagues also want to produce bioplastics that can serve as alternatives to problematic petrochemical products. Once disposed of, the soldier fly plastic is said to be biodegradable, so it doesn’t contribute to the current plastic pollution problem. Wooley’s vision is to effectively close the loop: “Ultimately, we want the insects to use the plastic waste again as a food source. In this way, it could in turn be used for the production of plastics again.”
Source: American Chemical Society, presentation at the American Chemical Society Meeting, August 13-17, 2023 in San Francisco