Scientists Discover Greener Way to Get Blue Jeans
What if blue plants could give denim its signature indigo hue?
A research team in Denmark has developed a new dyeing method that uses an enzyme for dyeing by leveraging a natural precursor to indigo called indicant that turns indigo plant leaves blue when mushed together.
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The enzyme would replace the more than 84,000 tons of sodium hydrosulfite used as a reducing agent to make the roughly 50,000 tons of synthetic indigo consumed by the global denim industry.
As outlined in a study published by Nature Communications, this technology could facilitate large-scale production and application of indican without the need for toxic chemicals.
“Indican is a natural compound made by indigo-producing plants and with the potential to be converted to indigo upon enzymatic treatment,” Ditte Hededam Welner, a biologist at the Novo Nordisk Foundation Center for Biosustainability and lead researcher on this new study, told Rivet.
Welner and the research team found that its engineered enzyme— PtUGT1-stable—is “extremely stable,” meaning it can withstand the industrial manufacturing process better than previous methods employing the precursor.
“[We found] that we could synthesize indican at high concentration (100 mM), which is crucial for economic feasibility,” Welner said. “The wildtype enzyme is dead at 100 mM indican.”
However, a bulk source of indican is missing, meaning that indican is not produced on a global scale, Welner explained, though they haven’t tried scaling it yet.
Indican is colorless, meaning that the compound must be converted into indigo after being applied to a material. Welner’s team achieved this by leaving it in the sunlight for a few hours.
“We got the idea that light can cleave indican to indoxyl, and we showed that it is indeed the case—natural sunlight, a household bulb, and energy-efficient LEDs all work to produce the blue color from indican,” Welner said. “And our new methods produce exactly the same hues as traditional indigo, so replacement is possible.”
Welner and her research team aren’t the only ones interested in replacing indigo.
Last October, AGI Denim inked a deal with sustainable indigo dye startup Huue, which uses microbial processes to create bio-based indigo.
“Our technology involves mirroring the way nature produces color; we’re programming microbes to use the same enzymatic reaction in plants to directly produce a high-purity indigo. What sets Huue apart is our focus on creating a bio-identical match,” Huue’s co-founder and CEO Michelle Zhu previously told Rivet. “This means that our technology provides the same performance and application as the petrochemical product, making it compatible with existing equipment in the denim industry and a true drop-in replacement.”
French bio-tech company Pili is also in the business of making high-performance bio-based indigo. Compared to classic petrochemical dyes, Pili states that its microorganisms produce the same amount of dye without petrol or chemicals, and need just one-fifth of the usual water amount while growing at room temperature.
