(191e) High Level Malic Acid Production From Polymalic Acid Fermentation by Aureobasidium Pullulans and Acid Hydrolysis

Xiang Zou^a, Yipin Zhou^b, Shang tian Yang^b*

(a.     College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, P.R China;

(b.    William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA)

Abstract

Malic acid, a C4-dicarboxylic acid, is widely used in the food industry and a potential C4 platform chemical in biorefinery. Malic acid is commercially produced either through hydration of fumaric or maleic acids under high temperature and pressure yielding a racemic mixture or via the enzymatic transformation of fumarate producing L-malic acid by immobilized bacterial cells. However, these processes require expensive raw materials such as petroleum-derivative maleic anhydride or costly enzymes, which have limited their economical competitiveness. Compared with these methods, microbial fermentation using relatively inexpensive substrates is a promising way for economical production of malic acid. However, the low product yield from conventional malic acid fermentation limits further industrialization efforts due to product inhibition. In this work, we developed a novel process for malic acid production from fermentation produced polymalic acid (PMA) followed with acid hydrolysis. First, a high-yield strain A. pullulans ZX10 was isolated, which produced PMA at a high titer equivalent to 87.6 g/l malic acid and high productivity of 0.61 g/l h in free-cell fed-batch fermentation. Repeated fed-batch fermentations with cells immobilized in a fibrous-bed bioreactor achieved the highest product titer of 144.2 g/l and productivity of 0.74 g/l h. The fermentation produced PMA was separated by ethanol precipitation and then purified by adsorption with IRA-900 resin, achieving a ~100% purity. Pure malic acid was then produced from PMA by acid hydrolysis. This process provides an efficient and economical way for PMA and malic acid production, and is promising for industrial application.