Bioproduction of riboflavin by fungi using spent industrial oils
Riboflavin (vitamin B2), an essential water-soluble vitamin is commercially produced because it cannot be synthesized by vertebrates. Although this vitamin is produced chemically, bioproduction is a better option since it is more economical, requires less energy, produces less waste and can use renewable sources. In this study we investigated spent oil from the food and motor industries as alternative cheap carbon sources for the bioproduction of this vitamin. Commercial fungal strains namely; Eremothecium gossypii ATCC 10895, Eremothecium gossypii CBS 109.51, Eremothecium ashbyi CBS 206.58 and the yeast, Candida famata ATCC 20850, as well as a laboratory mutated Eremothecium gossypii EMS 30/1 strain were used. Statistical experimental design using a series of fractional factorial experimental designs was used to optimize the effect of yeast extract, peptone, malt extract, K2HPO4 and MgSO4.7H2O to supplement the used oils for optimum riboflavin production. Response surface methodology based on central composite experimental designs was then applied and together with the point predictions made, production media for both substrates were further optimized. The optimized conditions were then tested with laboratory experiments. Results showed that mutant E. gossypii EMS 30/1 produced the most riboflavin in spent motor oil (20.45 mg.l-1) while Candida famata ATCC 20850 produced the highest concentration (16.99 mg.l-1) in spent vegetable oil. With these strains and using the experimental designs from the fractional factorial experiments, supplemented spent motor and spent vegetable oils produced 66.27 mg.l-1 and 72.50 mg.l-1 riboflavin, respectively. The central composite optimization results showed that 0.18 g.l-1 and 0.45 g.l-1 K2HPO4 and 12.5 g.l-1 malt extract increased the production to 91.88 mg.l-1 and 78.68 mg.l-1 in spent vegetable oil and motor oil respectively. A point prediction from the response surface methodology was used to validate these and it was found that 103.59 mg.l-1 riboflavin was produced by mutant E. gossypii EMS 30/1 using 2.5 g.l-1 yeast extract, 0.5 g.l-1 peptone, 12.5 g.l-1 malt extract, 0.18 g.l-1 K2HPO4 and 0.3 g.l-1 MgSO4.7H2O. After optimizing K2HPO4 in a one-factor-at-a-time experiment, 82.75 mg.l-1 riboflavin was produced by C. famataon v SVO using 6.5 g.l-1 peptone, 12.5 g.l-1 malt extract 0.15 g.l-1 K2HPO4 and 1.75 g.l-1 MgSO4.7H2O. This is a 5.08 and 4.87 fold increase respectively when compared to spent oil prior to optimization. This shows that spent motor oil and mutant E. gossypii produces 103.59 mg.l-1 riboflavin while spent vegetable oil and C. famata produces 82.75 mg.l-1 riboflavin. Hence, E. gossypii can be used to generate riboflavin using spent motor oil and C. famata, using spent vegetable oil.