Biodegradation of malachite green and rhodamine B by caecal microflora of rats

Bio-degradation of two non-permitted dyes namely Malachite green and Rhodamine B, commonly encountered in the food commodities, through rat caecal microflora was studied. Malachite green was biotransformed by caecal microflora to one fluorescent metabolite with a Rf value of 0.09. Incubation of Rhodamine B with caecal microflora resulted in two fluorescent metabolites with Rf values of 0.72 and 0.09. The DI50 value of Malachite green was quite low (10 min), while that of Rhodamine B could not be derived as the maximum degradation was only 32%. The results suggest that Malachite green and Rhodamine B are biotransformed to different metabolites by rat caecal microflora which may help in delineating the mechanism of carcinogenic potential of these two dyes.