The potential of papaya and banana peels as a substrate for Sphingomonas sp.pigment production: optimisation and antimicrobial activity

The need for colourants derived from natural sources and the change in consumer perception of synthetic colourants have opened the new potential for the natural colourant industry. As a result, due to its stability, high yield, and no seasonal variation, pigment derived from microorganisms is the best replacement for sources from plants and animals. Due to the high cost of synthetic media for microbial pigment production, it is necessary to design a new low–cost medium for microbial pigment production. This research aimed to examine the viability of banana and papaya peels as an alternative low-cost substrate for the yellow pigment-producing bacterium, AX1 strain (bacterium strain isolated from the anus of Holothuria (Lessonothuria) pardalis. AX1 was identified as Sphingomonas sp., an aerobic bacterium having Gram-negative, non-motile, rod-shaped bacteria. The optimal relative pigment concentration was achieved when the culture was cultivated in a medium containing the combination of dried papaya and banana with a ratio of 1:1 (100% v/v) at 37°C and pH 7 after 72 hrs incubation. The wavelength absorption was recorded at 468 nm. Various parameters including the effect of temperature, time, concentration, and pHs were used in this study. The pigment extraction showed a positive effect of antimicrobial activity against Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 25923, and Staphylococcus epidermidis ATTC 51625. The investigation of this study has shown that the combination of dried papaya and banana peels performed well as a substrate and may be used as a fermentation medium to replace the synthetic medium which is more expensive and less cost-effective for industrial application