Polymalic acid fermentation by Aureobasidium pullulans for malic acid production from soybean hull and soy molasses: Fermentation kinetics and economic analysis

Polymalic acid (PMA) production by Aureobasidium pullulans ZX-10 from soybean hull hydrolysate supplemented with corn steep liquor (CSL) gave a malic acid yield of similar to 0.4 g/g at a productivity of similar to 0.5 g/L.h ZX-10 can also ferment soy molasses, converting all carbohydrates including the raffinose family oligosaccharides to PMA, giving a high titer ( 71.9 g/L) and yield ( 0.69 g/g) at a productivity of 0.29 g/L.h in fed-batch fermentation under nitrogen limitation. A higher productivity of 0.64 g/L . h was obtained in repeated batch fermentation with cell recycle and CSL supplementation. Cost analysis for a 5000 MT plant shows that malic acid can be produced at $ 1.10/kg from soy molasses, $ 1.37/kg from corn, and $ 1.74/kg from soybean hull. At the market price of $ 1.75/kg, malic acid production from soy molasses via PMA fermentation offers an economically competitive process for industrial production of bio-based malic acid. (C) 2016 Elsevier Ltd. All rights reserved.