Thermal acid hydrolysis pretreatment, enzymatic saccharification and ethanol fermentation from red seaweed, gracilaria verrucosa

Abstract

The seaweed, Gracilaria verrucosa, was fermented to produce bioethanol. Optimal pretreatment conditions were determined to be 12% (w/v) seaweed slurry and 270 mM sulfuric acid at 121°C for 60 min. After thermal acid hydrolysis, enzymatic saccharification was carned out with 16 U/ml of mixed enzymes using Viscozyme L and Celluclast 1.5 L to G verrucosa hydrolysates. A total monosaccharide concentration of 50.4 g/l, representing 84.2% conversion of 60 g/l total carbohydrate from 120 g dw/l G verrucosa slurry was obtained by thermal acid hydrolysis and enzymatic saccharification. G verrucosa hydrolysate was used as the substrate for ethanol production by separate hydrolysis and fermentation (SHF). Ethanol production by Candida lusitaniae ATCC 42720 acclimated to high-galactose concentrations was 22.0 g/l with ethanol yield (YETOH) of 0-43. Acclimated yeast to high concentrations of specific sugar could utilize mixed sugars, resulting in higher ethanol yields in the seaweed hydrolysates medium.