Reduction Of Indigo Research Articles

Cathodic reduction of 2-hydroxy-1,4-naphthoquinone (lawsone) to generate 1,2,4-trihydroxynaphthalene as regenerable reducing agent for dispersed indigo

A central chemical step in the application of vat dyes is their reduction into the alkali soluble leuco-form. In denim production the indigo dye is reduced by catalytic hydrogenation, by use of a chemical stock vat or by cathodic electron transfer in presence of soluble mediator systems. In this study the potential of 2-hydroxy-1,4-anthraquinone (lawsone) to serve as reversible redox couple for indirect cathodic reduction of dispersed indigo was investigated. Results from cyclic voltammetry, voltammetry in flow cells equipped with different cathode material and batch electrolysis experiments in presence of dispersed indigo demonstrate successful electron transfer from cathodically reduced lawsone to dispersed indigo above pH 12.5. At this pH the di-anion of 1,2,4-trihydroxynaphthaline is present in solution. At lower pH e.g. pH 11.5 the mono-anion is present, which is not able to reduce indigo molecules. For the study synthetic chemicals have been used as a model, however when the chemically equivalent natural colorants henna and indigo are used instead a new route for a fully bio-based indigo dyeing becomes available.

Effect of Fermentation Scale on Microbiota Dynamics and Metabolic Functions for Indigo Reduction.

During indigo dyeing fermentation, indigo reduction for the solubilization of indigo particles occurs through the action of microbiota under anaerobic alkaline conditions. The original microbiota in the raw material (sukumo: composted indigo plant) should be appropriately converged toward the extracellular electron transfer (EET)-occurring microbiota by adjusting environmental factors for indigo reduction. The convergence mechanisms of microbiota, microbial physiological basis for indigo reduction, and microbiota led by different velocities in the decrease in redox potential (ORP) at different fermentation scales were analyzed. A rapid ORP decrease was realized in the big batch, excluding Actinomycetota effectively and dominating Alkalibacterium, which largely contributed to the effective indigo reduction. Functional analyses of the microbiota related to strong indigo reduction on approximately day 30 indicated that the carbohydrate metabolism, prokaryotic defense system, and gene regulatory functions are important. Because the major constituent in the big batch was Alkalibacterium pelagium, we attempted to identify genes related to EET in its genome. Each set of genes for flavin adenine dinucleotide (FAD) transportation to modify the flavin mononucleotide (FMN)-associated family, electron transfer from NADH to the FMN-associated family, and demethylmenaquinone (DMK) synthesis were identified in the genome sequence. The correlation between indigo intensity reduction and metabolic functions suggests that V/A-type H+/Na+-transporting ATPase and NAD(P)H-producing enzymes drive membrane transportations and energization in the EET system, respectively.

Production scale test for indirect cathodic reduction of indigo opens a route for greener denim

Textile and garment industry is one of the biggest industrial consumers of high quality water and belongs to most polluting industries worldwide. Development of textile chemical processes which allow reuse of chemicals and water thus is an imperative. Cathodic reduction of vat dyes e.g. indigo is a promising technology to replace non regenerable reducing agents in dyeing processes. Experiments at laboratory scale are not sufficient to achieve scalable results. In this study a full scale production test for replacement of dithionite based indigo reduction in denim production by cathodic dye reduction has been performed to demonstrate the potential of the technology. A 1000 A electrolyser was coupled to a open width yarn dyeing unit and 11,000 m (3,600 kg) of warp yarn was dyed with use of a cathodically regenerated iron-triethanolamine complex as reducing agent instead of a continuous dosage of dithionite into the dyebath. A time constant production was achieved over the full duration of the 5.5 h production. The dyed warp then was woven into denim fabric and only very minor colour deviations were observed between the electrochemically dye fabric and the reference quality, which demonstrates the ability of the technology to reproduce shade and ring-dying of a denim yarn. Model calculations to compare the chemical consumption of an electrochemical dye reduction with standard chemical processes indicate the importance of a recycling of the waste water by membrane filtration. Compared to a typical indigo range which consumes 100 g min−1 dithionite the chemical consumption of the new process falls below to 30% when 60% of the iron-complex therein is recovered. The demonstration of the technology in a full scale test can be understood as a relevant break through for future introduction of indirect cathodic dye reduction as cleaner technology in denim production.

Indigo reduction by using microorganism: Comparison of reducing power between Dietzia sp. KDB1 and yeast (Saccharomyces cerevisiae)

AbstractThis study aims to develop microbial indigo reduction by comparing the reducing power between Dietzia sp. KDB1 and yeast (Saccharomyces cerevisiae) at some reduction conditions. Oxidation–reduction potential (ORP), colour strength (K/S), and fluorescence intensity (FI) were applied to evaluate the reduction level as a function of microorganism concentration, pH, and glucose addition at 30°C. For both of the microbial systems, ORP decreased further −20 mV and K/S increased more than two by adding glucose. The reduction level became higher slightly by adding glucose, which played a role of metabolite in both of the reduction systems. Overall, reduction level of the yeast system was about a half of KDB1 system at the same reduction condition of 45 mL volume, 15 g/L natural indigo, 6 g/L reducing agents, pH 10.0, 30°C and glucose added.

The use of RGB-tracking of color changes during indigo-reduction processes based on LabVIEW machine vision.

The use of an RGB-tracking chart for monitoring the reduction of indigo (color changes) based on the LabVIEW machine vision is demonstrated for the first time. In contrast to a normal analytical chromatographic chart, the time scale is used on the X-axis, but the sum of "RGB-pixels" is used on the Y-axis, instead of "signal intensity". The RGB-tracking chart was obtained from an investigation of the process involved in the reduction of indigo, in which a PC camera was used as a detector and LabVIEW machine vision was simultaneously operated. As a result, when sodium dithionite (Na2S2O4) and yeast were used, respectively, during the indigo-reduction processes, two types of reduction processes were found; the optimized timing for dyeing can be easily determined from the RGB-tracking charts. Furthermore, based on the changes in HSV (hue, saturation, lightness), the use of sodium dithionite provides a higher number of hue and saturation when clothes & fabric were dyed. In contrast to this, a longer time was required for the yeast solution to reach the same high number for hue and saturation. After comparing several series of dyed fabrics, we found that the use of an RGB-tracking chart is indeed a reliable novel tool for measuring color changes that occur during the chemical reactions that are associated with this process.

Environmental factors contributing to the convergence of bacterial community structure during indigo reduction.

Indigo is solubilized through the reducing action of the microbiota that occurs during alkaline fermentation of composted leaves of Polygonum tinctorium L. (sukumo). However, the environmental effects on the microbiota during this treatment, as well as the mechanisms underlying the microbial succession toward stable state remain unknown. In this study, physicochemical analyses and Illumina metagenomic sequencing was used to determine the impact pretreatment conditions on the subsequent initiation of bacterial community transition and their convergence, dyeing capacity and the environmental factors critical for indigo reducing state during aging of sukumo. The initial pretreatment conditions analyzed included 60°C tap water (heat treatment: batch 1), 25°C tap water (control; batch 2), 25°C wood ash extract (high pH; batch 3) and hot wood ash extract (heat and high pH; batch 4), coupled with successive addition of wheat bran from days 5 to 194. High pH had larger impact than heat treatment on the microbiota, producing more rapid transitional changes from days 1 to 2. Although the initial bacterial community composition and dyeing intensity differed during days 2-5, the microbiota appropriately converged to facilitate indigo reduction from day 7 in all the batches, with Alkaliphilus oremalandii, Amphibacillus, Alkalicella caledoniensis, Atopostipes suicloalis and Tissierellaceae core taxa contributing to the improvement of when the dyeing intensity. This convergence is attributed to the continuous maintenance of high pH (day 1 ~) and low redox potential (day 2~), along with the introduction of wheat bran at day 5 (day 5~). PICRUSt2 predictive function profiling revealed the enrichment of phosphotransferease system (PTS) and starch and sucrose metabolism subpathways key toward indigo reduction. Seven NAD(P)-dependent oxidoreductases KEGG orthologs correlating to the dyeing intensity was also identified, with Alkalihalobacillus macyae, Alkalicella caledoniensis, and Atopostipes suicloalis contributing significantly toward the initiation of indigo reduction in batch 3. During the ripening period, the staining intensity was maintained by continuous addition of wheat bran and the successive emergence of indigo-reducing bacteria that also contributed to material circulation in the system. The above results provide insight into the interaction of microbial system and environmental factors in sukumo fermentation.

Improving Indigo Reduction to Leuco-Indigo by Glucose by Means of Direct Electron Transfer and Electron Carriers of Enzymes

Improving Indigo Reduction to Leuco-Indigo by Glucose by Means of Direct Electron Transfer and Electron Carriers of Enzymes

Electrocatalytic hydrogenation of indigo by NiMoS: energy saving and conversion improving.

An NiMo alloy bonded with sulfur (NiMoS) exhibits enhanced surface affinity toward water and organic molecules, thereby enhancing electrocatalytic hydrogenation (ECH) reactions through synergistic effects. In industrial processes, indigo, an ancient dye employed in the denim industry, is typically chemically reduced using sodium dithionite. However, this process generates an excess of toxic sulfide, which heavily contaminates the environment. ECH is a sustainable alternative for indigo reduction due to its reduced reliance on chemicals and energy consumption. In this study, carbon-felt (CF)-supported NiMoS was synthesized in a two-step process. First, the NiMo alloy was electrodeposited onto the CF surface, followed by sulfidation in an oven at 600 °C. NiMoS exhibits a larger electrochemically active surface area and a smaller charge transfer resistance compared to pure Ni and NiMo. Furthermore, NiMoS demonstrates excellent thermodynamic and kinetic properties for water splitting in strong alkaline solutions (1.0 M KOH). Additionally, optimal reaction conditions for the ECH of indigo were explored. Under the conditions of a 1.0 M KOH hydroxide medium with 10% methanol (v/v), an indigo concentration of 5 g L-1, a reaction temperature of 70 °C, and a current density of 10 mA cm-2, NiMoS/CF achieved remarkable improvements in both conversion (99.2%) and Faraday efficiency (38.1%). The results of this experimental work offer valuable insights into the design and application of novel catalytic materials for the ECH of vat dyes, opening up new possibilities for sustainable and environmentally friendly processes in the dye industry.

Indigofera tinctoria L. leaf powder promotes initiation of indigo reduction by inducing of rapid transition of the microbial community.

Water-insoluble indigo is solubilized by the reducing action of microorganisms which occurs during fermentation. In natural indigo fermentation, composted leaves of Polygonum tinctorium L. (sukumo) are the raw material that has been used as both the indigo source and the bacterial inoculum. Ideally, indigo reduction occurs shortly after preparation of the fermentation vat. The time-to-reduction depends on the quality of the sukumo and the methods for preparation and management of the fermentation batch. We estimated the effect of adding Indigofera tinctoria L. leaf powder (LP) to indigo fermentation in two fermentations originally exhibiting either rapid or slow time-to-reduction (T-sukumo and D-sukumo, respectively). Alkalihalobacillus spp. (97.7%–98.4% similarities with Alkalihalobacillus macyae) were observed only in the LP-added T-sukumo fermentation liquor. They appeared from day 1 (0.7%) and increased to 24.4% on day 6, and their presence was related to indigo reduction. Differences in functional ratio between LP-added and its control batches revealed enhancement of pathways related to reconstitution of cellular functions and substrate metabolisms, to all of which Alkalihalobacillus spp. contributed intensively. In D-sukumo batch, appearance of bacteria necessary to initiate indigo reduction (principally Anaerobacillus/Polygonibacillus) was comparatively slower. LP promotes earlier indigo reduction in both T- and D-sukumo-based batches, owing to its promotion of microbiota transition. The effect of the LP was intensified from day 1 to day 2 in both sukumo using batches according to the assumed function of the microbiota. The initial effect of LP on the T-sukumo batches was more intense than that in the D-sukumo batches and was continued until day 3, while the duration in the T-sukumo batches was continued until day 5. Based on these observations, we propose that the LP functions through its phytochemicals that eliminate oxygen, stimulate the microbiota, and accelerate its transitional changes toward a suitable function that opens the pathway for the extracellular electron transfer using carbohydrates as a substrate.

Fermentation Blues: Analyzing the Microbiota of Traditional Indigo Vat Dyeing in Hunan, China.

ABSTRACTTraditional indigo dyeing through anaerobic fermentation has recently gained worldwide attention in efforts to address concerns regarding the sustainability of industrial indigo dyeing and the impact of toxic reducing agents such as sodium dithionite (Na2S2O4) on human health and the ecological environment. Intriguingly, changes in the microbiota during indigo fermentation are known to potently affect the onset of indigo reduction, and thus elucidation of the microbial community transitions could help develop methods to control the initiation of indigo reduction. Here, we investigated the microbiota associated with the traditional indigo dyeing practiced in Hunan, China. Specifically, we identified the bacterial and fungal components of the microbiota at distinct stages in the indigo fermentation process by analyzing 16S rRNA gene and internal transcribed spacer sequences. Our analyses revealed two substantial changes in the microbiota during the traditional indigo fermentation process. The first change, which was probably caused by the introduction of Chinese liquor (featuring a high alcohol concentration), resulted in decreased bacterial diversity and increased proportions of Pseudomonas, Stenotrophomonas, and Bacillaceae family members. The second change, which could be attributed to the addition of specific plant species, led to an increase in the abundance of Alkalibacterium, Amphibacillus, the obligate anaerobe Turicibacter, the facultative anaerobe Enterococcus, and ZOR0006, as well as to a decrease in the pH and redox potential values. Our results indicate that the specific plant mixture included in the procedure here could be used as an effective additive to accelerate the initiation of indigo reduction during the fermentation process. To the best of our knowledge, this is the first report revealing the fungal diversity during the indigo fermentation process and, furthermore, showing that the fungal diversity has remained in transition despite the relatively stable bacterial diversity in the proper indigo fermentation process. Although traditional indigo fermentation in China is challenging to manage, we can benefit from local knowledge of the fermentation process, and understanding the scientific bases of traditional indigo fermentation will facilitate the development of environmentally friendly procedures.IMPORTANCE Chemical reducing agents included in modern indigo dyeing to initiate indigo reduction can be harmful to both human health and the environment. Given that traditional indigo dyeing involves natural fermentation in a dye vat using natural organic additives without the use of toxic chemicals and that changes in the microbiota during traditional indigo fermentation potently affect the onset of indigo reduction, elucidation of these microbial community transitions could help develop methods to control the initiation of indigo reduction. This study on the microbiota associated with the traditional indigo dyeing practiced in Hunan, China, has identified the bacterial and fungal communities at distinct stages of the indigo fermentation process. Notably, the addition of specific plant species might yield the desired microbial communities and appropriate fermentation conditions, which could be used as an effective additive to accelerate the initiation of indigo reduction. This study has also revealed the fungal diversity during the indigo fermentation process for the first time and shown that the fungal diversity has remained in transition despite the relatively stable bacterial diversity. Thus, this work provides new insights into the traditional indigo fermentation process used in China and substantially enhances current efforts devoted to designing environmentally friendly methods for industrial indigo dyeing.

Application of Fluorescence Spectroscopy in Indigo Reduction Process : Identification of Reduction Stages and Reduced Indigo Concentration

Application of Fluorescence Spectroscopy in Indigo Reduction Process : Identification of Reduction Stages and Reduced Indigo Concentration

Isolation and characterization of indigo-reducing bacteria and analysis of microbiota from indigo fermentation suspensions.

In natural indigo dyeing, the water-insoluble indigo included in the composted indigo leaves called sukumo is converted to water-soluble leuco-indigo through the reduction activities of microorganisms under alkaline conditions. To understand the relationship between indigo reduction and microorganisms in indigo-fermentation suspensions, we isolated and identified the microorganisms that reduce indigo and analyzed the microbiota in indigo-fermentation suspensions. Indigo-reducing microorganisms, which were not isolated by means of a conventional indigo carmine-reduction assay method, were isolated by using indigo as a direct substrate and further identified and characterized. We succeeded in isolating bacteria closely related to Corynebacterium glutamicum, Chryseomicrobium aureum, and Enterococcus sp. for the first time. Anthraquinone was found to be an effective mediator that facilitated the indigo-reduction activity of the isolated strains. On analysis of the microbiota in indigo-fermentation suspensions, the ratio of indigo-reducing bacteria and others was found to be important for maintaining the indigo-reduction activity.

Foaming indigo: An efficient technology for yarn dyeing

The global production of denim fabric is more than 9 billion meters, and indigo dye, an essential dye in the denim field, uses about 30–50 tons of water per million meters in the washing process after dyeing in order to remove the floating color. At present, the most common cotton yarn dyeing process is the traditional process of dyeing, using the multi-vat immersion dyeing method of the assembly line. In order to successfully reduce the water and energy consumption with the foaming process, it is necessary to combine the foam system by indigo reduction method. This study through the foam system selection and process optimization,The results showed the concentration of sodium dodecyl sulfate is 3 g/L, the concentration of citric acid is 1.2 g/L, the temperature is 50 °C, the speed is 1200r/min, and the stirring time is 5min. A simulated factory yarn-dyeing line was built, Through orthogonal test, sodium Hydrosulfite concentration and sodium hydroxide concentration required for 5 g/L indigo reduction were 7 g/L and 3 g/L, respectively. When the temperature was 80 °C, the reduction effect of indigo was the best. Taking the K/S value of cotton dyed with 5 g/L traditional process as the control, the required concentration of indigo dye foaming process was determined to be 14 g/L at 50 °C, and the foam indigo foaming technology was realized. By comparing the twist, single yarn strength, and hairiness tests of the dyed cotton yarn with the two technology, the results showed that the properties of the dyed cotton yarn with the foam indigo technology dye are better than the traditional technology. Compared with traditional technology, foam technology saves about 53.5% water and has an efficiency ratio of 1:10.

Indigofera tinctoria leaf powder as a promising additive to improve indigo fermentation prepared with sukumo (composted Polygonum tinctorium leaves).

Being insoluble in the oxidize form, indigo dye must be solubilized by reduction for it to penetrate textile. One of the procedures is the reduction by natural bacterial fermentation. Sukumo, composted leaves of Polygonum tinctorium, is a natural source of indigo in Japan. Although sukumo has an intrinsic bacterial seed, the onset of indigo reduction with this material may vary greatly. Certain additives improve indigo fermentation. Here, we studied the effects of Indigofera tinctoria leaf powder (LP) on the initiation of indigo reduction, bacterial community, redox potential (ORP), and dyeing intensity in the initial stages and in aged fermentation fluids prepared with sukumo. I. tinctoria LP markedly decreased ORP at day 1 and stabilised it during early fermentation. These effects could be explained by the phytochemicals present in I. tinctoria LP that act as oxygen scavengers and electron mediators. Using next generation sequencing results, we observed differences in the bacterial community in sukumo fermentation treated with I. tinctoria LP, which was not influenced by the bacterial community in I. tinctoria LP per se. The concomitant decrease in Bacillaceae and increase in Proteinivoraceae at the onset of fermentation, increase in the ratio of facultative to obligate anaerobes (F/O ratio), or the total abundance of facultative anaerobes (F) or obligate anaerobes (O) (designated F + O) are vital for the initiation and maintenance of indigo reduction. Hence, I. tinctoria LP improved early indigo reduction by decreasing the ORP and hasten the appropriate transitions in the bacterial community in sukumo fermentation.

The Mechanism Underlying of Long-Term Stable Indigo Reduction State in Indigo Fermentation Using Sukumo (Composted Polygonum tinctorium Leaves).

Indigo fermentation fluid maintains its indigo-reducing state for more than 6 months under open-air. To elucidate the mechanism underlying the sustainability of this indigo reduction state, three indigo fermentation batches with different durations for the indigo reduction state were compared. The three examined batches exhibited different microbiota and consisted of two phases. In the initial phase, oxygen-metabolizing-bacteria derived from sukumo established an initial network. With decreasing redox potential (ORP), the initial bacterial community was replaced by obligate anaerobes (mainly Proteinivoraceae; phase 1). Approximately 1 month after the beginning of fermentation, the predominating obligate anaerobes were decreased, and Amphibacillus and Polygonibacillus, which can decompose macromolecules derived from wheat bran, were predominantly observed, and the transition of microbiota became slow (phase 2). Considering the substrate utilization ability of the dominated bacterial taxa, the transitional change from phase 1 to phase 2 suggests that this changed from the bacterial flora that utilizes substrates derived from sukumo, including intrinsic substrates in sukumo and weakened or dead bacterial cells derived from early events (heat and alkaline treatment and reduction of ORP) to that of wheat bran-utilizers. This succession was directly related to the change in the major substrate sustaining the corresponding community and the turning point was approximately 1 month after the start of fermentation. As a result, we understand that the role of sukumo includes changes in the microbial flora immediately after the start of fermentation, which has an important function in the start-up phase of fermentation, whereas the ecosystem comprised of the microbiota utilizing wheat bran underpins the subsequent long-term indigo reduction.

Cu(II)/sodium borohydride-based electrocatalytic system for reduction and dyeing of indigo

PurposeTo improve the problems as the heavy burden of sewage treatment and environmental pollution caused by the traditional sodium hydrosulfite reduction dyeing of indigo, this study aims to carry out the direct electrochemical reduction dyeing for indigo with the eco-friendly Cu(II)/sodium borohydride reduction system under normal temperature and pressure conditions.Design/methodology/approachThe electrochemical behavior of Cu(II)/sodium borohydride reduction system was investigated by cyclic voltammetry. And, the dyeing performance of the Cu(II)/sodium borohydride reduction system was developed by optimizing the concentration of copper sulfate in the anode electrolyte, applied voltage and reduction time via single-factor and orthogonal integrated analysis.FindingsThe dyeing performance of the Cu(II)/sodium borohydride reduction system is superior to that of the traditional reduction dyeing with sodium hydrosulfite. In the case of the optimized condition, the soaping fastness and dry/wet rubbing fastness of the dyed fabric in the two reduction dyeing processes were basically comparable, the K/S value of electrocatalytic reduction of indigo by Cu(II)/NaBH4 is 11.81, which is higher than that obtained by traditional sodium hydrosulfite reduction dyeing of indigo.Originality/valueThe innovative electrocatalytic reduction system applied herein uses sodium borohydride as the hydrogen source combined with Cu(II) complex as the catalyst, which can serve as a medium for electron transfer and active the dye molecule to make it easier to be reduced. The electrochemical dyeing strategy presented here provides a new idea to improve the reduction dyeing performance of indigo by sodium borohydride.

Mao berry as a green reducing agent in natural indigo dyeing on cotton fabrics

In this work, mao berry extract was tested to determine whether it could be a green alternative reducing agent in the indigo dyeing on cotton fabrics. Glucose and fructose, which are the main reducing sugars in the extract, could reduce natural indigo pigment into its water soluble leuco form in the alkaline solution. Sodium hydroxide and calcium hydroxide were compared for their effectiveness in the alkaline reduction of indigo. The reduction potentials of the indigo dyebath using mao berry extract were evaluated with reference to the conventional reducing agent, sodium dithionite (Na2S2O4), and different reducing sugars. The results from colour strength and colour fastness to washing, light and rubbing of the dyed cotton fabrics using the extract were comparable with other reducing agents especially in NaOH. Mao berry extract gave satisfactory results as a green alternative to Na2S2O4 in the natural indigo dyeing process. Moreover, the UV protection ability of the dyed cotton fabrics was enhanced by the natural indigo dyes applied.

Electrochemical reduction of indigo by combination of sodium borohydride and copper salt

PurposeThe purpose of this study is to improve the performance of sodium borohydride in reducing indigo at room temperature, the divalent copper ion complex was combined with electrochemical technology for the reduction of indigo by sodium borohydride.Design/methodology/approachAccording to the K/S value of the dyed cloth sample, find a more suitable ligand for the copper ion in the catholyte. Response surface analysis tests were performed to evaluate the effects of sodium borohydride concentration, sodium hydroxide concentration and copper sulfate pentahydrate concentration on the reduction potential of the dye solution and the K/S value of the dyed fabric samples.FindingsSodium gluconate was found to be a more suitable ligand for copper ions in catholyte. The effects of NaOH concentration as well as the interaction of NaBH4 and NaOH on the reduction potential of the catholyte and the K/S value of the dyed fabric samples were extremely significant. The optimal concentrations of NaBH4, NaOH and CuSO4•5H2O were 0.5, 2.5 and 0.65 g/L. In the case of the optimized condition, the absolute value of the reduction potential was 968, and the K/S value was 11.92, which is comparable with that of the conventional reduction process with sodium dithionite.Originality/valueThe divalent copper ion complex combined with electrochemical technology was applied in the process of reducing indigo with NaBH4 at room temperature.

Eco-friendly Indigo Reduction by Using Dietzia sp. KDB1 Strain : Some Variables Required to Develop Process Technology

This study was aimed to develop the reduction process of natural indigo (Indigo/era tinctoria) by using bacterial strain (Dietzia sp. KDB1) separated from Korean traditional fermentation bath. In detail, changes in pH, oxidation reduction potential (ORP), and color intensity (K/S) of dyed ramie fabric were evaluated by using some of alkaline mediums, pH adjustments, and concentrations of KDB1 and indigo, respectively. In terms of pH control and reducing power, buffer solution of NaHCO3/NaOH was the most effective among the mediums used. In the baths with buffer solution, initial pH 10.7 exhibited faster initiation of reduction and higher K/S than other initial pH values. The bath adjusted at pH 10.0 showed higher K/S and more negative ORP, than the baths adjusted at pH 10.5 and 10.7. Better reducing power was obtained at higher indigo and KDB1 concentrations. With the combination of buffer solution, scale-up, repeat dyeing, and higher KDB1 concentration, K/S range of 9.5–16.0 was obtained at days of 4–6. Use of single bacterial strain for indigo reduction attains a simple, reliable and eco-friendly dyeing process which can be applied as an alternative to sodium dithionite reduction.

Mechanistic Insights into Indigo Reduction in Indigo Fermentation: A Voltammetric Study

Indigo is one of the oldest natural blue dyes. Microorganisms and their enzymatic activities are deeply involved in the traditional indigo staining procedure. To elucidate the mechanism of the microbial indigo reduction, we directly performed cyclic voltammetry on alkaline fermenting dye suspensions. A pair of characteristic redox peaks of leuco-indigo was observed in a supernatant fluid of the fermenting dye suspension. On the other hand, it was found that the indigo/leuco-indigo redox couple mediated two-way microbially catalyzed oxidation and reduction in a sediment-rich suspension of the fermenting suspension. Acetaldehyde was supposed to be the electron donor and acceptor of the catalytic reactions. In order to verify the bioelectrocatalytic reaction, we isolated indigo-reducing bacterium K2-3′ from the fermenting suspension, and the two-way bioelectrocatalysis was successfully restaged in a model system containing K2-3′ and methyl viologen (as a soluble mediator instead of indigo) as well as acetaldehyde at pH 10.