«To alleviate the problems associated with food waste, while simultaneously contributing to sustainable fashion». The problem statement tackled by scientist Akram Zamani
Fungi are ravenous microbes. When left to feed on moldy bread, they self-produced microscopic fibrous polymers. Scientists have been studying and treating them to create alternatives for leather, paper and even attempted spinning yarn.
Akram Zamani, principal investigator of the research, Fungal Textile Alternatives from Bread Waste at University of Borås, Sweden shares her hopes for the project.
«We hope they can replace cotton or synthetic fibers and animal leather, which can have negative environmental and ethical aspects». Since 2018, her team has run series of experiments to develop these materials, with the first prototypes presented at the American Chemical Society in March 2022.
Why leather and food waste make a sensible pair?
According to their presentation at ACS, the purpose of the project was multi-fold, «To alleviate the problems associated with food waste, while simultaneously contributing to sustainable fashion. [To investigate] the feasibility of making an alternative textile material with leather-like properties, from fungal biomass cultivated on bread waste».
Leather has evolved from ancient primitive clothing to a luxury commodity in the fashion industry. The global leather goods market is growing at 5.9% annually and valued over 349 billion USD in 2020; according to the International Trade Centre.
Apart from the environmental footprint of animal farming, the process of leather, in particular chrome tanning used to soften the leather, is detrimental; it leaks effluents like chromium, chlorides, sulphates and suspended solids in above acceptable concentrations.
On the other hand, FAO-UN states that global food waste generates over four giga tons of carbon dioxide equivalent or eight per cent of total anthropogenic GHG emissions. To draw a comparison, food waste’s footprint is almost equal to that of global road transport emissions.
Further, Sofie Svensson, doctoral student under Zamani shares «Bread waste is one of the biggest fractions of food wastage. We use bread waste for cultivation of filamentous fungi. This is used in production of new textile materials».
The team has also recently begun testing other types of food waste; including fruit and vegetable juices, in particular the mass left after juice is pressed from fruit.
«Instead of being thrown away, it could be used for growing fungi. So we are not limiting ourselves to bread, because hopefully there will be a day when there isn’t any bread waste» shares Zamani.
The process of fungal cultivation
A team of researchers went to the supermarket in search of sustenance for their subject – a filamentous fungus, Rhizopus delemar. Unsold, moldy supermarket bread was dried, ground into breadcrumbs and mixed with water in a thousand liter bioreactor.
To this vat, spores of the fungus were added and left to cultivate in a submersion. The fungi fed on the bread, producing microscopic natural fibers made of chitin and chitosan that accumulated in its cell walls. Within two days, the scientists were able to harvest the cells, subtracting lipids, proteins and other by-products.
The remaining jelly-like residue acts as the raw material for yarn and faux-leather. «The fungal cell walls contain fibrous biopolymer that can be spun into a yarn. The yarn can be woven into a fabric. It can also be used directly to product non-woven material», according to Svensson.
In the current study, the yield produced was 0.15 grams of biomass per gram of substrate. Records state that robust growth was displayed but the biomass required washing to clean away the bread particles unconsumed by the fungi.
Fungus to yarn and faux-leather sheets
The mucilaginous cell wall material is fibrous and was spun into yarn with ease. The scientists propose its use in medical sutures or wound-healing textiles due to anti-microbial properties. The suspension of fungal cells was also spread uniformly in order to dry out into sheets; they can be used as paper or leather substitutes.
However, the team encountered obstacles in mimicking the texture of leather as the initial prototypes were thin, inflexible, brittle-to-the-touch and almost transparent. To combat this, the biomass was subjected to a vegetable tanning pre-treatment, in the hopes of stabilizing the protein components.
This is perceived as a novel approach. Zamani confirms «To the best of our knowledge, this is the first-time vegetable tanning was researched on filamentous fungi to produce textile alternatives with leather-like properties».
Vegetable tannins are plant-based compounds used to convert animal hides into leather by enhancing the flexibility and resistance to heat and microbial degradation. The rationale behind this approach is rooted in sustainable procedures.
«In developing our process, we have been careful not to use toxic chemicals or anything that could harm the environment» shares Zamani, who maintains that the goal of the research work was to design a bio-based material without using high energy consuming processes and harmful chemicals.
Results were promising as the sheets made from tannin treated fungal biomass showed increased flexibility and opacity, tinged with a brown hue. However, post-treatments were still needed to augment mechanical performance as the drying process created minor wrinkling.
This was tackled using a wet-laid method, glycerol soaking. A solution of twenty per cent glycerol in water was used to immerse the fungal sheets for an hour. Post-drying, flexibility increased as the spaces between polymers increased by penetration of glycerol, which is hygroscopic in nature.
Scalability and future prospects of bread-fungi leather
There is an increasing demand for sustainably produced leather alternatives to address the environmental issues of the leather and leather goods industry. Zamani’s team furthers that cause by valorising food waste in a two-fold step towards mitigating the climate change crisis.
«The fungal fibers that we are using for production of the textiles are not only renewable but also in many cases, they are bio-compatible and show some anti-microbial properties. Therefore we believe, in the end, the fungal textiles will have very high potential for different applications, especially in medical textiles». Facilitating scalability, pending further research, is the adoption of common processes used in biotechnology, leather and paper industries.
Sustainable faux-leather alternatives in the market
In a 2021 study by Meyer, natural leather was compared to nine diverse commercially sold leather substitutes that were either bio-based or petro-chemical based. It revealed that none of the alternatives could substantially mimic the quality and properties of naturally produced leather. Further, the study showed that environmentally adverse substances were used in coatings and reinforcement layers.
Despite this, faux-leather fabricated from bio compunds has paved many promising roads for large-scale production. Case in point: Mylo, which was developed using mycelium (mushroom) grown on sawdust, ZOA, collagen-based with genetically modified yeast, made using similar proteins to those present in animal hides and Piñatex, popularly known pineapple fibre.
However, the scientists believe that there is a lack of this knowledge in academia with few studies reported. One such study was presented in 2019 by García and Prieto; it evaluated a potential leather-like material to substitute footwear leather from Komagataeibacter, a bacterial strain that can synthesise cellulose.
Unfortunately, its water absorption properties wiped off the possibility of its application as a leather-substitute. In this race, fungi-generated leather has high prospects in planet-friendly production and decomposition.
Competitive advantages of bread-fungi leather
Zamani can ascertain that commercial leather alternatives are made from harvested mushrooms or by growing fungi in a thin layer over sawdust. This process utilises solid state fermentation to cultivate the fungi. She explains that this method require weeks to produce enough fungal material.
In comparison, her team’s process uses a submerged in water cultivation process that is completed in forty eight hours. Another competitive advantage is the completely natural production of their leather with vegetable tannins from chestnut wood and glycerol as opposed to synthetic coatings on other commercially available products.
Research scientist at University of Borås and principal investigator of the research: Fungal Textile Alternatives from Bread Waste. Her team recently presented their study at a convention by the American Chemical Society in March 2022. Further experimentation is being carried by her team out with other food waste for fungal cultivation.