초록
<P><B>Abstract</B></P> <P>Guayule rubber production leaves >80% biomass as ground bagasse, which can be hydrolyzed to release sugars but also fermentation inhibitors. Here inhibitor generation and sugar conversion by the CO<SUB>2</SUB>-H<SUB>2</SUB>O pretreatment and enzyme hydrolysis were studied. Different pretreatment conditions: 550–4900 psi, 160–195 °C, 10–60 min and fixed 66.7% water, generated widely varying amounts of inhibitors (per dry-bagasse mass): 0.014–0.252% hydroxymethylfurfural, 0.012–0.794% furfural and 0.17–8.02% acetic acid. The condition (195 °C/3400 psi/30 min) giving highest reducing sugar (86.9 ± 1.5%) and cellulose (99.2 ± 1.3%) conversions generated more inhibitors. <I>Kluyveromyces marxianus</I> fermentation showed complete growth and ethanol production inhibition at ≥14 g/L combined inhibitors. Considering both sugars and inhibitors, the optimum condition was 180 °C, 1800 psi and 30 min, enabling 82.8 ± 2.8% reducing sugar, 74.8 ± 4.8% cellulose and 88.5 ± 6.9% hemicellulose conversions with low levels of hydroxymethylfurfural (0.07%), furfural (0.25%) and acetic acid (3.0%). The optimized CO<SUB>2</SUB>-H<SUB>2</SUB>O pretreatment gave much lower inhibitor formation and higher sugar conversion than other pretreatment methods.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Filled critical knowledge gap of inhibitor generation by CO<SUB>2</SUB>-H<SUB>2</SUB>O based pretreatment. </LI> <LI> Optimum condition for high sugar-low inhibition hydrolysis: 1800 psi, 180 °C, 30 min. </LI> <LI> 83–87% reducing sugar conversion in combined pretreatment and enzyme hydrolysis. </LI> <LI> 0.07% (w/w) HMF, 0.25% furfural and 3.0% acetic acid formation per guayule mass. </LI> <LI> <I>Kluyveromyces marxianus</I> ethanol production inhibited by 14 g/L combined inhibitors. </LI> </UL> </P>