Experimental design to enhance the production of L-(+)-lactic acid from steam-exploded wood hydrolysate using Rhizopus oryzae in a mixed-acid fermentation

The fermentation of hemicellulosic hydrolysate from Pinus taeda chips, usin g the fungal culture Rhizopus oryzae, was carried out to produce L-(+)-lact ic acid and to optimize and enhance the biological conversion of reducing s ugar into L-(+)-lactic acid using the experimental design to evaluate the c ulture conditions. The first factorial design based on surface response wit h five factors (agitation level, substrate concentration, CaCO3 concentrati on, C/N and C/P ratios) at low levels and one medium point was performed to optimize culture conditions. The second study tested two factors (substrat e concentration and C/N ratio) at three levels. The statistical analysis of the data obtained from the factorial study showed that a C/N ratio of 35 a nd substrate concentration of 90 g/litre were the best conditions to produc e L-(+)-lactic acid with R. oryzae on P. taeda hydrolysate, but in this cas e the statistical projection was not correct and the real optimized conditi ons were C/N ratio of 55 and substrate concentration of 75 g/litre of reduc ing sugar. (C) 1999 Elsevier Science Ltd. All rights reserved.