Enzymatic saccharification of agar waste from Gracilaria verrucosa and Gelidium latifolium for bioethanol production

Worldwide, 9600 t of agar is produced annually. Meanwhile, 60% of the waste produced from the agar industry yearly do not get treated. Our present study aims to study the enzymatic saccharification of solid agar waste produced from two of the most widely used agarophytes in the agar industry, Gracilaria verrucosa and Gelidium latifolium. Gracilaria species are the most common raw material in the food grade agar industry, while Gelidium species are the most common raw material used for bacteriological and pharmaceutical purposes because of the high-quality agar that is produced from these species. Our results showed that waste generated from agar extraction still contained sugars which could be optimized by acid pretreatment and enzymatic saccharification. Gracilaria verrucosa resulted in a higher agar yield (35.15 ± 1.17%), but produced less agar waste (20.91 ± 0.43%) than G. latifolium. After sequential acid pretreatment and enzymatic saccharification of the agar waste, the agar waste hydrolysate of G. latifolium resulted in higher glucose, galactose, and ethanol production, and a higher ethanol yield (18.17 ± 0.75, 16.17 ± 2.07, and 10.83 ± 0.30 g L−1 and 0.33 g g−1, respectively) than G. verrucosa. The results from our present study may be used to optimize biorefinery utilization of G. verrucosa and G. latifolium.