Enhanced Production of 6-(N-Hydroxyethyl)-Amino-6-Deoxy-α-L-Sorbofuranose by Immobilized Gluconobacter oxydanson Corn Stover with a pH Control Strategy in a Bubble Column Bioreactor.

6-(N-Hydroxyethyl)-amino-6-deoxy-α-L-sorbofuranose (6NSL) is a key intermediate in the synthesis of miglitol. Biotransformation of N-2-hydroxyethyl glucamine (NHEG) to 6NSL was performed by immobilized Gluconobacter oxydans, which was prepared by cultivating the cells in a home-made bubble column bioreactor where corn stover particles were loaded. The optimal carrier addition and aeration rate for 6NSL production by immobilized cells in the bioreactor were determined to be 25 g/L and 2.5 vvm respectively. The supplementation of NH4Cl was conducive to the biotransformation of NHEG and was performed by adding aqueous ammonia and HCl, which was taken as the pH controlling agents as well. An optimal pH control strategy using the mixture of aqueous ammonia and NaOH was applied, resulting in a 9.9% increased production of 6NSL, while repeated batches of biotransformation increased from three times to four times. Finally, the 6NSL concentration and the conversion rate of NHEG to 6NSLreached 44.2 ± 1.5 g/L and 88.4 ± 2.0%, respectively, in average after four cycles of biotransformation under the optimized condition.