Study and uncover the green fermentation mechanism in the traditional indigo dyeing vat

Natural indigo is one of the oldest dyes in the
world.
In industrial indigo staining, the conversion of indigo into a soluble staining solution requires the use of a strong reducing agent sodium disulfite (_Na2S2O4), which has serious implications
for the ecological environment and human health.

Traditional indigo dyeing is still being done worldwide in various forms, and dyers use natural organic additives to configure dyeing vats for dyeing
.
But this is a complex fermentation process, and there are differences
in the recipes and various additives used by dyers of different regions, different ethnic groups, and even the same ethnic group in the same region.

To uncover the inner mechanisms and principles of traditional dyeing vats, the study investigated and examined six "hot spots" in
Southeast Asia and China, including Timor-Leste, India, Indonesia, Laos, the Philippines and Vietnam, where indigo-producing plant diversity is distributed.
Through the analysis of bibliometrics, combined with the field survey results of the research team for many years, the theoretical system of the system involved in the traditional indigo staining process was summarized, and 8 hypotheses
of plant addition were proposed.

Studies have found that the traditional indigo dyeing process is particularly clever, can effectively dissolve indigo, first dye blue and then black
.
The study documented 80 species of plants used in the dyeing process from blue to black, belonging to 39 families and 67 genera
.
Based on the reasons for plant utilization obtained from field investigations (including the preparation of grass and wood ash water, winemaking, fermentation recipes, accelerated fermentation, increased dyeing fastness, ceremonial plants that can bring good luck to newly formulated dyeing tanks), and the effective chemical or microbial substances (including reducing sugars, endogenous bacteria, quinones, flavonoids, tannins, and metal ions) contained in plants that have been confirmed in modern research, and the functions of these effective substances (including the ability of grass and wood ash water as an alkaline medium, Rice wine provides a source of carbon and nitrogen for microbial growth, flavonoids can be used as electronic donors, anthraquinone compounds can be used as electronic mediators, reducing sugars can be used as green reducing agents, some anaerobic bacteria can directly reduce indigo, tannins and indigo combined variable black, and metal ions can be used as mordants), the study puts forward eight hypotheses for the use of organic additives: providing an alkaline environment, providing functional microorganisms, providing substrates for microbial growth, providing electronic donors, providing electronic mediators, providing reducing sugars, As well as the provision of metal mordants or tannin mordants
.
Based on the existing research on dyeing theory, combined with eight hypotheses, the study developed an explanatory model of the traditional blue-black dyeing process for the first time, which initially clarified why ordinary people added these specific plants to the
dyeing tank.

The hypotheses and theories derived from the study pave the way for indigo staining using natural plant products instead of chemical additives, providing a green path
for industrial cleaner production.
The study bridges the gap between traditional knowledge and scientific principles and highlights the need for further experimental work to test the hypothesis of adding plant products to dyeing vats, hopefully providing a scientific method and theoretical basis for the application of
environmentally friendly dyeing techniques.

The findings are titled Blue to Black: Hypotheses on plant use complexity in traditional dyeing processes in Southeast Asia and China published in Industrial Crops & Products, a leading journal in the
field.
Li Shan is the first author of the paper, and researcher Wang Yuhua is the corresponding author
.
The research was supported
by the Strategic Pilot Special Projects of the Chinese Academy of Sciences (No.
XDA20050204, XDA19050301 and XDA19050303) and the Second Qinghai-Tibet Plateau Comprehensive Scientific Expedition Research Project (No.
2019QZKK0502).

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Figure 1 Sources of lye water in different regions

Fig.
2 Theoretical schematic diagram of traditional indigo dyeing process