- Open Access
Eco-friendly indigo reduction using bokbunja (Rubus coreanus Miq.) sludge
© Shin et al.; licensee Springer 2014
- Received: 18 January 2014
- Accepted: 17 March 2014
- Published: 8 July 2014
The utilization of Bokbunja (Rubus coreanus) sludge as a source of reductant was investigated to develop an eco-friendly indigo dyeing process. Total sugar contents were 18.94 and 50.87% for ethanol and water extracts, respectively. The extract was effective to reduce indigo dye. Reduction of indigo was occured rapidly in the solution containing the extract and indigo dye in alkaline condition and it reached to the maximum color yield in one or two day. The reduction potential of the extract was stabilized between -550 mV and -600 mV depending on concentration of the extract. At higher concentration of the extract, reduction power was maintained stably for longer time and stronger color yield. It was confirmed that the Bokbunja sludge extract can be an eco-friendly and safe alternative to sodium dithionite as a reducing agent in indigo dyeing processes.
- Bokbunja (Rubus coreanus) sludge
- Indigo dyeing
- Reduction potential
- Color yield
Extract yield and total sugar of extract powder
Total sugar (%)
The indigo dye is insoluble in water and cannot be used for dyeing without reducing. So, the reduction of indigo to leuco-indigo represents a critical wet process in textile industry, which is operated worldwide on a large scale for the dyeing of denim and blue jean products. In most industrial indigo dyeing process, sodium dithionite is used mainly due to powerful reduction of indigo. However, it generates non-regenerable oxidation products and causes various problems in the disposal of the dyebath and the washing water. After several decades of research and development there is still no commercial reducing technology available today that can replace sodium dithionite in all areas of vat dye applications. There have been previous attempts to replace sodium dithionite as reducing agents for dyeing with vat dyes wholly or partly by reducing sugars such as glucose (Meksi et al. 2012), fructose, lactose, galactose and maltose (Blackburn and Harvey, 2004).
The aim of this study is to investigate the utilization of Bokbunja sludge extract as a natural organic reducing agent for indigo dyeing. Extraction was carried out using water and ethanol and their effectiveness was compared in terms of yield, total sugar content, and antioxidant activity to determine better extraction medium. The reducing power of the water extract of Bokbunja sludge was evaluated by measuring reduction potential and color yield.
Bokbunja sludge was provided by Bokbunja Wine Company, Gochang, Korea. It was stored in a refrigerator. Synthetic indigo (Sigma) and 100% ramie fabric (density; 60×46/in2, weight;118 g/m2, thickness;0.32 mm) were purchased commercially. All the chemicals and reagents were of analytical grade.
Extraction of bokbunja sludge
Dried Bokbunja sludge samples (50 g) were added to an Erlenmeyer flask with 1 L distilled water and then refluxed at 100°C for 60 min. Extracted solution was filtered, concentrated under vacuum using a rotary evaporator, shock frozen at −80°C and frozen-dried at −50°C to give a crude extract powder. Ethanol (70%) extract was carried out at room temperature for 24 h with agitation using an inverter and thereafter, same procedures with water extract described in above were followed. The crude extract powder was used without purification.
Total carbohydrate content
Total carbohydrate analysis was done by a phenol-sulfuric acid method (Masukoa et al. 2005; Saha and Brewer, 1994). Absorbance was measured by UV–vis spectrophotometer at 490 nm, using glucose as a standard sugar.
DPPH radical scavenging activity
Reduction process of indigo
A solution containing 0.5 g of synthetic indigo, 5 g of calcium hydroxide and an appropriate amount of the Bokbunja sludge extract powder were prepared by adding them to 150 ml of distilled water. This solution was brought up to 80°C. Reduction potential was measured at 60°C using a Bioanalytical Systems CV-27 Voltammograph (BAS, USA), which incorporated a platinum band electode and an Ag-AgCl reference electrode.
The reaction medium obtained from the reduction process of indigo as previously described was used as a dyebath. Namely, indigo vat of 150 ml was prepared by adding 0.5 g of indigo, calcium hydroxide (5 g) with varied amount of the water extract powder and temperature of the vat brought up to 80°C. Fabric was dipped in the indigo vat at 60°C for 20 min, followed by exposed in air, and washed in distilled water with soap. After neutralizing in acetic acid solution, dyed samples were rinsed and dried in open air for further evaluation.
The reflectance of the dyed sample was measured at the maximum adsorption wavelength on a Macbeth Coloreye 3100 spectrophotometer. Absorbance of the extract solution was measured using a UV–vis spectrophotometer (Agilant 8453, Agilant Technologies, Waldbronm, Germany).
Total sugar content of bokbunja sludge extract
Extraction yields were 7.2 and 9.7% on the weight of dried Bokbunja sludge with ethanol and water, respectively. Total sugar contents of the extract were 18.94 and 50.87% for ethanol and water extracts, respectively (Table 1). Considering higher yield and sugar content, water was more effective solvent for extracting Bokbunja sludge.
A previous study (Ku and Mun, 2008) revealed that hot water extracts of Bokbunja pulp contained neutral sugars (69.9%) such as glucose, fructose, and sucrose as well as anthocyanin (5.2%). Considering total sugar content, it was speculated that the Bokbunja sludge extract prepared in this study also contained reducing sugars and so, it can be used as a reducing agent in indigo dyeing. Reducing sugars have been used for reduction processes as possible benign alternative reducing agents for indigo (Meksi et al., 2012) and sulfur dyes (Blackburn and Harvey, 2004). Their reducing effect is associated with an electron-rich intermediate (Vuorema et al. 2009). Employment of food by-products as a source of reducing sugars has the advantage that harmful environmental effects can be avoided.
DPPH radical scavenging activity of the bokbunja sludge extract
DPPH radical scavenging activity indicates the ability of inhibiting oxidation of the extract. It is widely used to characterize antioxidant activity of plant material (Arnao, 2000). Anthocyanins in Bokbunja are phenolics, exhibiting antioxidant activity, and their molecules are unstable and highly susceptible to degradation by pH, temperature, light, sugars, etc. (Eiro and Heinonen, 2002).
From the results obtained, it was considered that the Bokbunja sludge extracts can be used as a natural antioxidant and the water extract was more effective compared to the ethanol extract. Antioxidant activity of the Bokbunja sludge extract would have a positive effect on the stability of reduction process because it could prevent leuco-indigo from oxidizing to indigo by scavenging reactive oxygen species (Moure et al., 2001).
Reducing power of the bokbunja sludge extract
From the results of reduction potential and color yield measurements, it was confirmed that the Bokbunja sludge extract could be an eco-friendly and safe alternative to sodium dithionite as a reducing agent in indigo dyeing processes.
Reduction mechanism of indigo using the extract
The utilization of Bokbunja (Rubus coreanus) sludge as a source of reductant was investigated to develop an eco-friendly indigo dyeing process. The water extract showed relatively high DPPH radical scavenging activity and contained high sugar content of 50.87%. The extract was effective to reduce indigo dye. The reduction of indigo was occured with the Bokbunja sludge extract rapidly at 80°C and the maximum color yield was reached in one or two days. The reduction potential of the extract was stabilized at about −550 ~ −600 mV depending on concentration of the extract. At higher concentration of the extract, reduction lasted for longer time and higher color yield was obtained. It was confirmed that the Bokbunja sludge extract could be an eco-friendly and safe alternative to sodium dithionite as a reducing agent in indigo dyeing processes.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2013029705).
- Arnao, MB. (2000). Some methodological problems in the determination of antioxidant activity using chromogen radicals: a practical case. Trends Food Science and Technology, 11, 419–421.View ArticleGoogle Scholar
- Blackburn, RS, & Harvey, A. (2004). Green chemistry methods in sulfur dyeing: application of various reducing D-sugars and analysis of the importance of optimum redox potential. Environmental Science & Technology, 38, 4034–4039.View ArticleGoogle Scholar
- Blois, MS. (1958). Antioxidant determinations by the use of a stable free radical. Nature, 181, 1199–1200.View ArticleGoogle Scholar
- Bozic, M, & Kokol, V. (2008). Ecological alternatives to the reduction and oxidation processes in dyeing with vat and sulphur dyes. Dyes and Pigments, 76, 299–309.View ArticleGoogle Scholar
- Choi, HS, Kim, MK, Park, HS, Kim, YS, & Shin, DH. (2006). Alcoholic fermentation of bokbunja (Rubus coreanus Miq.) wine. Korean Journal of Food Science and Technology, 38, 543–547.Google Scholar
- Eiro, MJ, & Heinonen, M. (2002). Anthocyanin color behavior and stability during storage: effect of intermolecular copigmentation. Journal of Agricultural and Food Chemistry, 50, 7461–7466.View ArticleGoogle Scholar
- Ku, CS, & Mun, SP. (2008). Characterization of seed oils from fresh bokbunja (Rubus coreanus Miq.) and wine processing waste. Bioresource Technolology, 99, 2852–2856.View ArticleGoogle Scholar
- Masukoa, T, Minamib, A, Iwasakib, N, Majimab, T, Nishimura, S-I, & Leea, YC. (2005). Carbohydrate analysis by a phenol–sulfuric acid method in microplate format. Anaytical Biochemistry, 339, 69–72.View ArticleGoogle Scholar
- Meksi, N, Ticha, MB, Kechida, M, & Mhenni, MF. (2012). Using of ecofriendly α-hydroxycarbonyls as reducing agents to replace sodium dithionite in indigo dyeing processes. Journal of Cleaner Production, 24, 149–158.View ArticleGoogle Scholar
- Moure, A, Cruz, JM, Franco, D, Domı’nguez, JM, Sineiro, J, Domı’nguez, H, & Nu’n˜ez, MJ. (2001). Natural antioxidants from residual sources. Food Chemistry, 72, 145–171.View ArticleGoogle Scholar
- Peschel, W, Sa’nchez-Rabaneda, F, Diekmann, W, Plescher, A, Gartzı’a, I, Jime’nez, D, Lamuela-Ravento’s, R, Buxaderas, S, & Codina, C. (2006). An industrial approach in the search of natural antioxidants from vegetable and fruit wastes. Food Chemistry, 97, 137–150.View ArticleGoogle Scholar
- Saha, AK, & Brewer, CF. (1994). Determination of the concentrations of oligosaccharides, complex type carbohydrates, and glycoproteins using the phenol-sulfuric acid method. Carbohydrate Research, 254, 157–167.View ArticleGoogle Scholar
- Vareed, SK, Reddy, MK, Schutzki, RE, & Nair, MG. (2006). Anthocyanins in cornus alternif olia, cornus controversa, cornus kousa and cornus florida fruits with health benefits. Life Science, 78, 777–784.View ArticleGoogle Scholar
- Vuorema, A, John, P, Keskitalo, M, Mahon, MF, Kulandainathand, MA, & Marken, F. (2009). Anthraquinone catalysis in the glucose-driven reduction of indigo to leuco-indigo. Physical Chemistry Chemical Physics, 11, 1816–1824.View ArticleGoogle Scholar
- Yoon, I, Wee, JH, Moon, JH, Ahn, TH, & Park, KH. (2003). Isolation and identification of quercetin with antioxidative activity from the fruits of rubus coreanum Miquel. Korean Journal of Food Science and Technology, 35, 499–502.Google Scholar
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