Deep eutectic solvent-oriented integration of eco-friendly and efficient indican extraction and enzyme-based indigo preparation

Abstract

Indigo, one of the oldest dyes, finds widespread usage across multiple industries, encompassing food, medicine, printing, dyeing, as well as cosmetics. Indican is recognized as a precursor substance crucial for the synthesis of indigo, however, the current indican extraction and indigo preparation are largely limited due to the low efficiency of indican extraction, by-product production, as well as serious environmental pollution. To address the serial of issues, we developed deep eutectic solvent (DESs)-oriented integration of the efficient extraction of indican and the green preparation of indigo from Strobilanthes cusia (Nees) Kuntze. DESs were rationally designed and screened to make them able to destroy cell walls to facilitate the precipitation of the desired substance for specific indican extraction. And then optimized to obtain the final extraction rate of 22.8mg/g, which present the highest so far. More importantly, without additional treatment for DES-containing indican extractive, the β-glucosidase Asbg1 was able to convert indican to indigo at a molar conversion rate of 74.6%. By fully harnessing plant resources, the study introduced an innovative process that bypassed extreme acid-base conditions, ensuring rapidness and minimal pollution. This approach offered a promising avenue for the preparation of indigo, paving the way for sustainable production methods.