BACKGROUNDPolymalic acid (PMA) is a water-soluble polyester with many attractive properties for biomedical application. Its monomer L-malic acid is widely used in the food industry and is also a potential C4 platform chemical. Hydrolysate of raw sweet potato as a low-cost renewable feedstock was applied for the production of PMA by immobilized Aureobasidium pullulans cells in an aerobic fibrous bed bioreactor system (AFBB). RESULTSUnder the initial hydrolysate sugar concentration 120gL(-1), yeast extract 5gL(-1), and citrate 7.5gL(-1), PMA production in a shake flask was improved. Comparison of the kinetics of fed-batch immobilized-cell fermentation using the AFBB with those of batch or fed-batch free-cell fermentation in a 5L fermentor showed that immobilized-cell fermentation gave much higher PMA production and productivity. The maximum PMA production and productivity in AFBB were 57.5gL(-1) and 0.34gL(-1)h, which was 30.6% and 21.4% higher than that in free-cell mode. CONCLUSIONRaw sweet potato is an efficient renewable feedstock for PMA fermentation. This present work demonstrated the great potential of AFBB and renewable feedstocks for the economical production of PMA and malic acid at industrial scale. (c) 2013 Society of Chemical Industry