High temperature and low acid pretreatment and agarase treatment of agarose for the production of sugar and ethanol from red seaweed biomass

To obtain fermentable sugar from agarose, pretreatment of agarose by using acetic acid was conducted for short durations (10–30 min) at low acid concentrations (1–5% (w/v)) and high temperatures (110–130 °C). On testing the pretreated agarose by using an endo-β-agarase I (DagA), an exo-β-agarase II (Aga50D), and neoagarobiose hydrolase (NABH), we observed that the addition of the endo-type agarase did not increase the sugar yield. Use of the crude enzyme of Vibrio sp. EJY3 in combination with Aga50D and NABH including acetic acid pretreatment resulted in a 1.3-fold increase in the final reducing sugar yield (62.8% of theoretical maximum based on galactose and 3,6-anhydrogalactose in the initial agarose), compared to those obtained using Aga50D and NABH only after acetic acid pretreatment. The simultaneous saccharification and fermentation of pretreated agarose yielded ethanol of 37.1% theoretical maximum yield from galactose contained in the pretreated agarose.