Study proposes sustainable leather production from bread fungi

This Wednesday (23), research was presented at the spring meeting of the American Chemical Society (ACS) that describes how scientists harnessed a fungus to convert food waste into sustainable synthetic leather, as well as paper products and cotton substitutes. , and with properties comparable to traditional materials.

Will your next fashion bag be made from “fungus leather”? Whether this will be applied anytime soon remains to be seen, but fungal leather, according to its discoverers, takes less time to produce than substitutes already on the market and, unlike most of them, is 100% bio-based.

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Like textiles and petroleum-based leather, cotton production is associated with environmental concerns. At the same time, a lot of food goes to waste. Faced with this scenario, the Ph.D. from the University of Borås, Sweden, Akram Zamani decided to make use of new sustainable, bio-based materials derived from fungi. “We hope they can replace cotton or synthetic fibers and animal leather, which can have negative environmental and ethical aspects,” says Zamani, the project’s principal researcher. “When developing our process, we were careful not to use toxic chemicals or anything that could harm the environment.”

To feed the fungal organisms, the team collected stale bread from the supermarket, which they dried and ground into crumbs. The researchers mixed the bread crumbs with water in a pilot-scale reactor and added spores of the species Rhizopus delemar, which can normally be found in decaying food.

As this fungus fed on the bread, it produced microscopic natural fibers made of chitin and chitosan that built up in its cell walls. After two days, the scientists collected the cells and removed lipids, proteins and other byproducts that could be used in food or feed.

In turn, the remaining gelatinous residue, consisting of the fibrous cell walls, was then organized into threads, which could be used in sutures or wound-healing fabrics and perhaps in clothing.

Alternatively, fungal cells were laid out horizontally to be dried to make paper or leather-like materials. According to Zamani, the first fungal leather prototypes the team produced were thin and not flexible enough.

Now, the group is working on thicker versions that consist of multiple layers to more closely mimic real animal leather. These composites include layers treated with tree-derived tannins – which give the structure softness – combined with alkali-treated layers that give it strength.

In addition to strength, flexibility and gloss were also improved by treatment with glycerol and a bio-based binder. “Our recent tests show that fungal leather has mechanical properties quite comparable to real leather,” says Zamani.

Thread derived from the fungus Rhizopus delemar, which can be used in the production of biodegradable leather. Image: University of Borås

Types of fungus leather available on the market are not biodegradable.

Some other fungal leathers have already reached the market, however, little information about their production has been published, and their properties still do not correspond to real leather, according to Zamani.

As far as she can tell, commercial products are made from harvested mushrooms or fungi grown in a thin layer over food scraps or sawdust by solid-state fermentation.

According to Zamani, these methods require several days or weeks to produce enough fungal material, while fungus submerged in water takes just a few days to produce the same amount of material. Some other researchers are also experimenting with submerged cultivation, but on a much smaller scale than the efforts of Zamani’s team.

In addition, some of the fungal leathers already available on the market contain environmentally harmful coatings or reinforcement layers made from synthetic petroleum-based polymers such as polyester. This is in contrast to the products from the University of Borås team, which only consist of natural materials and will therefore be biodegradable.

Zamani says his team is working to further refine its fungal products. They’ve also recently started testing other types of food waste, including fruits and vegetables. An example is the paste that is left over after the juice is squeezed from the fruit. “Instead of being thrown away, it could be used to grow fungi”, says the scientist. “So we are not limiting ourselves to bread, because we hope that a day will come when there is no waste of bread.”

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