No abstract

Thermoascus aurantiacus is able to secrete most of the hemicellulolytic and cellulolytic enzymes. To establish the xylanase inducers of T. aurantiacus, the mycelia were first grown on glucose up until the end of the exponential growth phase, followed by washing and re-suspension in a basal medium without a carbon source. Pre-weighed amounts of xylose (final concentration of 3.5 mg/ml), xylobiose (7 mg/ml) and hydrolyzed xylan from sugarcane bagasse (HXSB) which contained xylose, xylobiose and xylotriose (6.8 mg/ml) were evaluated as inducers of xylanase. It was observed that xylose did not suppress enzyme induction of T. aurantiacus when used in low concentrations, regardless of whether it was inoculated with xylobiose. Xylobiose promoted fast enzyme production stopping after 10 h, even at a low consumption rate of the carbon source; therefore xylobiose appears to be the natural inducer of xylanase. In HXSB only a negligible xylanase activity was determined. Xylose present in HXSB was consumed within the first 10 h while xylobiose was partially hydrolyzed at a slow rate. The profile of α-arabinofuranosidase induction was very similar in media induced with xylobiose or HXSB, but induction with xylose showed some positive effects as well. The production profile for the xylanase was accompanied by low levels of cellulolytic activity. In comparison, growth in HXSB resulted in different profiles of both xylanase and cellulase production, excluding the possibility of xylanase acting as endoglucanases.

Milagres, pela orientação, amizade, confiança e disponibilidade. Ao meu pai, Marcelo Monte, pelo exemplo de sabedoria, força e persistência. Ao meu namorado Marcio Glielmo, pela paciência, amor e incentivo constante. Aos meus irmãos Marcelo, Regina, Isabel e Elisa que mesmo à distância sempre me incentivaram, apoiaram e confiaram em mim. Aos meus primos Eleonora e Valmir, pela atenção, confiança, incentivo e amor.

Sugarcane bagasses from three experimental sugarcane hybrids and a mill-reference sample were used to compare the efficiency and mode of action of acid and alkaline sulfite pretreatment processes. Varied chemical loads and reaction temperatures were used to prepare samples with distinguished characteristics regarding xylan and lignin removals, as well as sulfonation levels of residual lignins. The pretreatment with low sulfite loads (5%) under acidic conditions (pH 2) provided maximum glucose yield of 70% during enzymatic hydrolysis with cellulases (10 FPU/g) and β-glucosidases (20 UI/g bagasse). In this case, glucan enzymatic conversion from pretreated materials was mostly associated with extensive xylan removal (70-100%) and partial delignification occurred during the pretreatment. The use of low sulfite loads under acidic conditions required pretreatment temperatures of 160°C. In contrast, at a lower pretreatment temperature (120°C), alkaline sulfite process achieved similar glucan digestibility, but required a higher sulfite load (7.5%). Residual xylans from acid pretreated materials were almost completely hydrolysed by commercial enzymes, contrasting with relatively lower xylan to xylose conversions observed in alkaline pretreated samples. Efficient xylan removal during acid sulfite pretreatment and during enzymatic digestion can be useful to enhance glucan accessibility and digestibility by cellulases. Alkaline sulfite process also provided substrates with high glucan digestibility, mainly associated with delignification and sulfonation of residual lignins. The results demonstrate that temperature, pH, and sulfite can be combined for reducing lignocellulose recalcitrance and achieve similar glucan conversion rates in the alkaline and acid sulfite pretreated bagasses. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:944-951, 2018.