Enzymatically hydrolysed molasses and sodium citrate as new potentials for the improvement of canthaxanthin batch synthesis by Dietzia natronolimnaea HS-1: A statistical media optimisation

Response surface methodology-central composite rotatable design (RSM-CCRD) was applied to explore the optimum media formulation for maximising canthaxanthin (CTX) biosynthesis by Dietzia natronolimnaea HS-1. The effects of three variables of enzymatically hydrolysed molasses (EHM) (16.6-33.4 g/l), sodium (Na)-citrate (21.64-28.36mM), and yeast extract (6.32-9.68 g/l) concentrations on the production of CTX, total carotenoid (TCT), and biomass dry weight (BDW) were appraised. The results showed that the quadratic effects of EHM, yeast extract, and Na-citrate contents in terms of second-order polynomial regression equations (R2 = 0.968-0.986), respectively, had the most significant effects on the produced TCT and CTX. The predicted maximum accumulation of BDW (8.88 g/l), TCT (7.24 mg/l), and CTX (6.40 mg/l) under the optimum concentrations of the media variables (26.16 g/l EHM, 8.29 g/l yeast extract, and 25.86mM Na-citrate) was very close to the experimental values determined in batch experiments. The high BDW content suggested EHM and Na-citrate as very promising feedstocks for CTX bioproduction by the bacterium studied.