BIOLOGICAL CONVERSION OF HEMICELLULOSE TO PROPIONIC-ACID

A mixture of endo- and exoxylanases were used to produce a hemicellulo se hydrolysate containing 29.6 g L-1 of xylose equivalents based on re ducing sugars analysis. Propionibacterium acidipropionici was grown in a 2-l batch reactor in mineral salts medium containing 60% (v/v) hemi cellulose hydrolysate, 5 g l(-1) proteose peptone, and 2.5 g l(-1) yea st extract. Propionic acid production was growth associated. The maxim um specific growth rate and maximum specific propionic acid production rate were 0.1 and 0.23 g g(-1) h(-1), respectively. Growth and acid p roduction were inhibited at propionic acid concentrations greater than 2 g l(-1). The final concentration of propionic acid attained was 18 g l(-1). This study demonstrates the feasibility of propionic acid pro duction by P. acidipropionici on an enzymatically hydrolyzed hemicellu losic fraction of steam-exploded Populus tremuloides. (C) 1998 Elsevie r Science Inc.