초록
<P>Co‐cultures for simultaneous production of ethanol and xylitol were studied under different operation bioreactor modes using <I>Candida tropicalis</I> IEC5‐ITV and <I>Saccharomyces cerevisiae</I> ITV01‐RD in a simulated medium of sugarcane bagasse hydrolyzates. Xylitol and ethanol tolerance by <I>S.？cerevisiae</I> and <I>C. tropicalis</I>, respectively, was evaluated. The results showed that <I>C. tropicalis</I> was sensitive to ethanol concentrations up to 30？g/L, while xylitol had no effect on <I>S.？cerevisiae</I> viability and metabolism. The best condition found for simultaneous culture was <I>S.？cerevisiae</I> co‐culture and <I>C. tropicalis</I> sequential cultivation at 24 h. Under these conditions, productivity and yield for ethanol were <I>Q</I><SUB>EtOH</SUB>？=？0.72？g？L<SUP>−1</SUP> h<SUP>−1</SUP> and <I>Y</I><SUB>EtOH/s</SUB>？=？0.37？g/g, and for xylitol, <I>Q</I><SUB>XylOH</SUB>？=？0.10？g？L<SUP>−1</SUP> h<SUP>−1</SUP> and <I>Y</I><SUB>XylOH/S</SUB>？=？0.31？g/g, respectively; using fed‐batch culture, the results were <I>Q</I><SUB>EtOH</SUB>？=？0.87？g？L<SUP>−1</SUP> h<SUP>−1</SUP> and <I>Y</I><SUB>EtOH/s</SUB>？=？0.44？g？L<SUP>−1</SUP>？h<SUP>−1</SUP>, and <I>Q</I><SUB>EtOH</SUB>？=？0.27？g？L<SUP>−1</SUP>？h<SUP>−1</SUP> and <I>Y</I><SUB>EtOH/s</SUB>？=？0.57？g/g, respectively. Maximum volumetric productivity in continuous multistep cultures of ethanol and xylitol was at dilution rates of 0.131 and 0.074？h<SUP>−1</SUP>, respectively. Continuous multistep production, <I>Q</I><SUB>EtOH</SUB> increased up to 50% more than in fed‐batch culture, even though xylitol yield remained unchanged.</P>