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Application of the Severity Factor and HMF Removal of Red Macroalgae Gracilaria verrucosa to Production of Bioethanol by Pichia stipitis and Kluyveromyces marxianus with Adaptive Evolution

Sukwong, Pailin, Sunwoo, In Yung, Lee, Min Ju, Ra, Chae Hun, Jeong, Gwi-Taek, Kim, Sung-Koo
Applied biochemistry and biotechnology 2019 v.187 no.4 pp. 1312-1327
Gracilaria verrucosa, Kluyveromyces marxianus, Scheffersomyces stipitis, acid hydrolysis, bioethanol, biomass, carbohydrate content, ethanol, ethanol production, evolutionary adaptation, fermentation, galactose, hydroxymethylfurfural, macroalgae, saccharification, slurries, sulfuric acid, yeasts
Gracilaria verrucosa, red seaweed, is a promising biomass for bioethanol production due to its high carbohydrate content. The optimal hyper thermal (HT) acid hydrolysis conditions are 12% (w/v) G. verrucosa with 0.2 M H₂SO₄ at 130 °C for 15 min, with a severity factor of 1.66. This HT acid hydrolysis produces 50.7 g/L monosaccharides. The maximum monosaccharide concentration of 58.0 g/L was achieved with 96.6% of the theoretical monosaccharide production from 120 g dry weight/L G. verrucosa slurry after HT acid hydrolysis and enzymatic saccharification. Fermentation was carried out by removing an inhibitory compound and via yeast adaptation to galactose. Both Pichia stipitis and Kluyveromyces marxianus adapted to galactose were excellent producers, with the ethanol yield (YEₜOH) of 0.50 and 29.0 g/L ethanol production. However, the bioethanol productivity with Pichia stipitis adapted to galactose is higher than that with Kluyveromyces marxianus adapted to galactose, being 0.81 and 0.35 g/L/h, respectively. The results from this study can be applied to industrial scale bioethanol production from seaweed.