BACKGROUND: Effects of co-substrate sorbitol different feeding strategies on recombinant human growth hormone (rhGH) production by Pichia pastoris hGH-Mut + were investigated by eight designed experiments grouped as: (i) fed-batch methanol feeding without the co-substrate; (ii) fed-batch methanol feeding with pulse sorbitol feeding; (iii) fed-batch methanol feeding together with fed-batch sorbitol feeding at t = 0-15 h, followed by fed-batch methanol feeding; and (iv) fed-batch methanol and sorbitol feeding at t = 0-30 h, followed with fed-batch methanol feeding. RESULTS:The highest rhGH and cell concentrations were achieved, respectively, as 0.64 g L −1 and 105 g L −1 at t = 42 h of induction phase, with the strategy where methanol was fed to the system at a pre-determined feeding rate of µ M0 =0.03 h −1 , and sorbitol concentration was kept at 50 g L −1 at t = 0-15 h of the rhGH production phase where the specific growth rate on sorbitol was µ S0 =0.025 h −1 . The overall cell and product yield on total substrate were found as 0.26 g g −1 and 2.26 mg g −1 , respectively. CONCLUSION: This work demonstrates that co-carbon source, sorbitol, feeding strategy is as important as methanol feeding strategy in recombinant protein production by Mut + strains of P. pastoris.

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