2.3. Alkaline delignification
The alkaline extractions were performed with milled native
cane bagasse (1 mm particle size in average) in 500 mL Erlenmeyer
flasks containing 5 wt% TS, using an agitation of 200 rpm during
30 min in an Ultronique Q5.9/37A ultrasonic bath. First, a preliminary
study was carried out to evaluate the effect of ultrasound on
alkali delignification. The alkali loading in these experiments was
0.5 g of NaOH g−1 of native bagasse (dry basis) and extraction was
done at 80 ◦C for 30 min using 0 and 163 W of sonication power.
Once the beneficial effect of ultrasound was demonstrated, the
sono-assisted alkaline delignification of cane bagasse was preoptimized
using a central composite design with two replicates at
the center point for a total of 16 experiments (Table 1). The variables
tested were temperature (◦C), NaOH concentration (g g−1 TS)
and sonication power (W). After delignification, the resulting substrates
were filtered and washed with a fresh NaOH solution at the
same concentration used before, followed by several water washing
steps until a neutral pH was reached.
Small fractions of both alkali-washed (AWB) and sono-assisted
alkali-washed (SA-AWB) cane bagasse were separated and characterized
as described below. The remaining materials were stored at
4 ◦C in vacuum-sealed bags until further use.