Effects of furfural on anaerobic continuous cultivation of Saccharomyces cerevisiae

Furfural is an important inhibitor of yeast metabolism in lignocellulose-de rived substrates. The effect of furfural on the physiology of Saccharomyces cerevisiae CBS 8066 was investigated using anaerobic continuous cultivatio ns. Experiments were performed with furfural in the feed medium (up to 8.3 g/L) using three dierent dilution rates (0.095, 0.190, and 0.315 h(-1)). Th e measured concentration of furfural was low (< 0.1 g/L) at all steady stat es obtained. However, it was not possible to achieve a steady state at a sp ecific conversion rate of furfural, q(f), higher than approximately 0.15 g/ g.h. An increased furfural concentration in the feed caused a decrease in t he steady-state glycerol yield. This agreed well with the decreased need fo r glycerol production as a way to regenerate NAD(+), i.e., to function as a redox sink because furfural was reduced to furfuryl alcohol. Transient exp eriments were also performed by pulse addition of furfural directly into th e fermentor. In contrast to the situation at steady-state conditions, both glycerol and furfuryl alcohol yields increased after pulse addition of furf ural to the culture. Furthermore, the maximum specific conversion rate of f urfural (0.6 g/g.h) in dynamic experiments was significantly higher than wh at was attainable in the chemostat experiments. The dynamic furfural conver sion could be described by the use of a simple Michaelis-Menten-type kineti c model. Also furfural conversion under steady-state conditions could be ex plained by a Michaelis-Menten-type kinetic model, but with a higher anity a nd a lower maximum conversion rate. This indicated the presence of an addit ional component with a higher anity, but lower maximum capacity, either in the transport system or in the conversion system of furfural. (C) 2001 John Wiley & Sons, Inc.