Indigo dyeing onto ramie fabric via microbial reduction: Reducing power evaluation of some bacterial strains isolated from fermented indigo vat

This research is to examine the reducing power of bacterial single strain and the mixture of strains. Four strains of Dietzia sp. KDB1 (KC433534), Nesterenkonia sp. KDB2 (KC433535), Nesterenkonia sp. KDB3 (KC433536), and Nesterenkonia sp. KDB4 (KC433537) separated from the fermented indigo vat were cultivated in aerobic condition. Natural indigo of the niram powder obtained from the water extract of Polygonum tinctorium and synthetic indigo purchased was used after sterilization. Natural and synthetic indigo samples were reduced with the strains in an incubator. Oxidation/reduction potential and pH of the mixture of indigo and strain(s) solutions were measured at the same intervals of elapsed time. Dyeing test was applied to evaluate the reduction power of bacterial strains isolated. Ramie fabric was used for the indigo dyeing and its color strength was determined from the reflectance at 660 nm and expressed as K/S values by using a spectroscope. CIELAB coordinates were measured with the same spectroscope and H V/C values were obtained by using the conversion program. All the strains showed reducing power onto natural and synthetic indigo samples. With the elapsed time, dye-uptake was increased up to maximum dye-uptake, and then decreased. The potential was dropped rapidly around −500 mV and then changed very slightly maintaining lower than −400 mV. The pH measured was decreased with the elapsed time. All the hue values obtained were of bluish purple (PB) shade. On the reducing power represented as dye-uptake, KDB1 strain was the highest among the strains selected for natural indigo and KDB3 strain for synthetic indigo. KDB2 showed the lowest for both of natural and synthetic indigo. Mixture of strains shortened the start time of reduction and that of maximum dye-uptake than any single strain.