Selective oxidation of trimethylolpropane to 2,2-bis(hydroxymethyl)butyric acid using growing cells of Corynebacterium sp. ATCC 21245

• Conversion of polyols to hydroxycarboxylic acid by whole cells biotransformation.
• Selective oxidation of trimethylolpropane (TMP) using Corynebacterium sp.
• Enhancement of oxidation in presence of co-substrates.
• pH 8 and 1 v/v/m airflow are optimal conditions for the oxidation process.
• Product recovery using ion exchange resin.

Multifunctional chemicals including hydroxycarboxylic acids are gaining increasing interest due to their growing applications in the polymer industry. One approach for their production is a biological selective oxidation of polyols, which is difficult to achieve by conventional chemical catalysis. In the present study, trimethylolpropane (TMP), a trihydric alcohol, was subjected to selective oxidation using growing cells of Corynebacterium sp. ATCC 21245 as a biocatalyst and yielding the dihydroxy-monocarboxylic acid, 2,2-bis(hydroxymethyl)butyric acid (BHMB). The study revealed that co-substrates are crucial for this reaction. Among the different evaluated co-substrates, a mixture of glucose, xylose and acetate at a ratio of 5:5:2 was found optimum. The optimal conditions for biotransformation were pH 8, 1 v/v/m airflow and 500 rpm stirring speed. In batch mode of operation, 70.6% of 5 g/l TMP was converted to BHMB in 10 days. For recovery of the product the adsorption pattern of BHMB to the anion exchange resin, Ambersep® 900 (OH−), was investigated in batch and column experiments giving maximum static and dynamic binding capacities of 135 and 144 mg/g resin, respectively. BHMB was separated with 89.7% of recovery yield from the fermentation broth. The approach is applicable for selective oxidation of other highly branched polyols by biotransformation.