Indican—a colourless compound derived from indigo-producing plants—could reduce the environmental and societal impacts associated with dying jeans by around 90% because it does not need toxic chemicals, researchers have found.
- Their study, published in the journal Nature Communications, suggests ditching the classic dye altogether.
- The researchers engineered a variant of an enzyme found in the indigo-producing plant that could produce indican on an industrial scale. Indican, however, could be slightly more expensive than traditional dye.
THE INDIGO ISSUE: Scientists have been searching for ways to make a more sustainable form of indigo, used for centuries to colour textiles, but which in its modern synthetic form needs toxic chemicals, large quantities of water and is linked to substantial carbon dioxide emissions.
- Indigo is the only known molecule yielding the unique and beloved hue of blue denim. It is a vat dye requiring harsh reducing agents such as dithionite and alkaline conditions for dyeing.
- Indigo dyeing has significant negative environmental and social implications, including pollution of waterways and soil with concomitant crop loss, as well as human toxicity.
- Indican, the β-O-glucoside of the indigo precursor indoxyl, is the natural storage form of indigo in indigo-producing plants. It has been suggested as an environmentally mild blue denim dyeing agent since indican dyeing would eliminate reducing agents while still ending as indigo in the yarn.
- To efficiently leverage indican in denim dyeing, two processes must be developed that have environmental benefits over the conventional method while still being affordable: a production process and a dyeing process.
THE RESEARCH: The scientists addressed these two aspects, considering the three dimensions of sustainability, i.e. (1) economic viability, (2) environmental performance, and 3) social impacts.
- To achieve economically feasible indican production, they engineered a stabilised glycosyltransferase mutant to convert indoxyl to indican at high substrate titers, a process with little environmental impact and no significant social impact.
- They demonstrated economically feasible and low-impact enzymatic and light-driven denim dyeing processes, which have the potential to alleviate the current pressure on textile workers’ health and livelihood.
- The study found light-driven dyeing could cut the environmental damage of traditional indigo dyeing by 73%, while using the enzyme could slash the impacts by up to 92%. In both cases, the classic blue jean colour turns up the same as when conventional indigo is used.
- If indican were to replace indigo to dye the nearly four billion jeans traded annually, there would be a significant reduction in production of toxic waste and global CO2 emissions.
- While they said production of indican would still require polluting petrochemicals, so would not be significantly better than producing synthetic indigo, the benefits come when the dye is put to use.
- Indican in powdered form can be dissolved in water then used on fabric and activated with either an enzyme or exposure to light.
THE RESEARCHERS: Ditte Hededam Welner a researcher at the Novo Nordisk Foundation Center for Biosustainability Enzyme Engineering and Structural Biology, is the corresponding author.
- The other researchers are Gonzalo Nahuel Bidart, David Teze, Eleonora Pasutto, Natalia Putkaradze, Folmer Fredslund and Sumesh Sukumara from the Novo Nordisk Foundation Center; Charlotte Uldahl Jansen and Katrine Qvortrup from the Department of Chemistry at the Technical University of Denmark; Anna-Mamusu Sesay from the 3Lab for Sustainability and Design, Designskolen Kolding; Leila Lo Leggio from the Department of Chemistry at the University of Copenhagen’; and Olafur Ögmundarson from the Faculty of Food Science and Nutrition at the University of Iceland.
- The authors, who have a published patent for their study, acknowledged limitations to their work, including a lack of facilities to simulate indican production at scale.
