Voltammetric in-situ monitoring of leuco-indigo in indigo-fermenting suspensions

Cyclic voltammetry was successfully applied to in-vivo monitoring of leuco-indigo in indigo-fermenting suspensions under quiescent conditions without deoxygenation; the working and counter electrodes were kept on the surface of each suspension by a polyethylene vinyl alcohol tube holder. The anodic peak current was used as a measure of the leuco-indigo concentration. The voltammetric wave shape suggested partial solubilization of the indigo with some macromolecules in the fermenting suspensions, which lead to an in-situ method without any electrode surface pretreatment. The anodic peak current well reflected the dyeing activity of a suspensions. The results obtained for laboratory-level fermentation systems clarified the number of days required for dye fermentation, the effectiveness of addition of old suspension as an additive for preparing fresh fermenting suspensions, and the importance of addition of a nitrogen-based nutrient as well as a glucose-based one to recover the indigo-reducing activity. The method can also be applied to determine the amounts of indigo in used dye suspensions and extracts of fermented indigo leaves (sukumo) by adding a chemical reduction pretreatment. (C) 2021, The Society for Biotechnology, Japan. All rights reserved.

Automated summary

This study successfully applied cyclic voltammetry to in-vivo monitoring of leuco-indigo in indigo-fermenting suspensions, revealing no need for deoxygenation under quiescent conditions. The anodic peak current was used as a measure of leuco-indigo concentration. The method, which does not require electrode surface pretreatment, can reflect the dyeing activity of suspensions and clarify aspects such as the number of days required for dye fermentation and the importance of specific nutrient additions.