Production of polymalic acid and malic acid by Aureobasidium pullulans fermentation and acid hydrolysis

Malic acid is a dicarboxylic acid widely used in the food industry and also a potential C4 platform chemical that can be produced from biomass. However, microbial fermentation for direct malic acid production is limited by low product yield, titer, and productivity due to end-product inhibition. In this work, a novel process for malic acid production from polymalic acid (PMA) fermentation followed by acid hydrolysis was developed. First, a PMA-producing Aureobasidium pullulans strain ZX-10 was screened and isolated. This microbe produced PMA as the major fermentation product at a high-titer equivalent to 87.6g/L of malic acid and high-productivity of 0.61g/Lh in free-cell fermentation in a stirred-tank bioreactor. Fed-batch fermentations with cells immobilized in a fibrous-bed bioreactor (FBB) achieved the highest product titer of 144.2g/L and productivity of 0.74g/Lh. The fermentation produced PMA was purified by adsorption with IRA-900 anion-exchange resins, achieving a approximate to 100% purity and a high recovery rate of 84%. Pure malic acid was then produced from PMA by hydrolysis with 2M sulfuric acid at 85 degrees C, which followed the first-order reaction kinetics. This process provides an efficient and economical way for PMA and malic acid production, and is promising for industrial application. Biotechnol. Bioeng. 2013; 110: 2105-2113. (c) 2013 Wiley Periodicals, Inc.