Keywords: moist heat sterilisation, azo dyes, electron donors, microbial decolourisation, autoclaving, bioremediation, carbon sources, temperature, pressure
Transformation of azo dyes during moist heat sterilisation: a potential source of error in microbial decolourisation
This paper presents the role of moist heat sterilisation in decolourisation of azo dyes during autoclaving itself, thereby leading to over estimation of actual decolourisation through subsequent microbial process. This surprise phenomenon was probed in detail by studying the effects of temperature, pressure and role of electron donor/carbon sources on decolourisation. In the presence of 10 g/litre glucose, 75% decolourisation of Reactive Black 5 (RB-5) dye was observed after autoclaving of medium at 121°C for 15 min at 15 psi. Studies repeated with other azo dyes revealed that Reactive Orange 16 (RO-16) was affected by autoclaving whereas Reactive Red 11 (RR-11) and Reactive Red 141 (RR-141) did not show significant decolourisation. The reduction of dye was dependent on concentration of electron donor/carbon source and autoclave conditions. The results indicate that investigators must screen the dyes for decolourisation during autoclaving and choose the appropriate means of sterilisation to remove the artifice or incorporate correction factor for dye concentration at the start of experiment.