Bioethanol production from Gracilaria verrucosa using Saccharomyces cerevisiae adapted to NaCl or galactose

Abstract

This study examined the pretreatment, enzymatic saccharification, and fermentation of the red macroalgae Gracilaria verrucosa using adapted saccharomyces cerevisiae to galactose or NaCl for the increase of bioethanol yield. Pretreatment with thermal acid hydrolysis to obtain galactose was carried out with 11.7% (w/v) seaweed slurry and 373 mM HSO at 121 °C for 59 min. Glucose was obtained from enzymatic hydrolysis. Enzymatic saccharification was performed with a mixture of 16 U/mL Celluclast 1.5L and Viscozyme L at 45 °C for 48 h. Ethanol fermentation in 11.7% (w/v) seaweed hydrolysate was carried out using Saccharomyces cerevisiae KCTC 1126 adapted or non-adapted to high concentrations of galactose or NaCl. When non-adapted S. cerevisiae KCTC 1126 was used, the ethanol productivity was 0.09 g/(Lh) with an ethanol yield of 0.25. Ethanol productivity of 0.16 and 0.19 g/(Lh) with ethanol yields of 0.43 and 0.48 was obtained using S. cerevisiae KCTC 1126 adapted to high concentrations of galactose and NaCl, respectively. Adaptation of S. cerevisiae KCTC 1126 to galactose or NaCl increased the ethanol yield via adaptive evolution of the yeast.

Third generation bioethanol from invasive macroalgae Sargassum muticum using autohydrolysis pretreatment as first step of a biorefinery

“…The maximum ethanol yield for Ethanol Red ® was 87.7% (9.95 g of ethanol/L), while PE2 and the laboratory strain CEN.PK 113-7D were near of 100% (11.65 and 11.32 g of ethanol/L, respectively). In only 8.5 h, ethanol yields between 87 and 95% are achieved, pretty much faster than with other macroalgae and/or pretreatments [35,36]. As example, after 8.5 h of SSF, the yields obtained with the different strains were 87.1% with Ethanol Red ® (instead maximum values of 87.7% at 23.6 h), 95.3% with PE2 and 94.4% with CEN.PK 113-7D (instead 100% after 28.6 h), that means 93e99% of maximum yield in only 8.5 h.…”

Systematic review and perspective on the progress of algal biofuels

“…The ethanol yield of red seaweeds is relatively lower than green ones, but there are still efficient species. Ethanol yield of G. verrucosa will be 0.48 g ethanol/g algae [46]. As for microalgae, there are few kinds which have lower ethanol yield than macroalgae.…”

Bioethanol from macroalgae: Prospects and challenges

“…In order to obtain higher ethanol, hydrolysis of glucan as well as non-glucan with the fermentation of the resulting sugars is essential [60]. Sugar released from the pretreatment process has been fermented using microorganisms such as yeast, bacteria, and fungi, which ferment these sugars to produce ethanol as a by-product [41,110]. Saccharomyces cerevisiae is the commonly used yeast microorganism for fermentation as it readily ferments glucose [111].…”

“…Bioethanol production from macroalgae utilized commercial yeast strains such as S. cerevisiae KCTC 1126 [110,111], MTCC 180 [60], IAM 4178 [70], ATCC 24858 [97], KCTC 17574 [52], Pichia stipitis [125], Pichia angophorae [114], Scheffersomyces stipitis [108], Brettanomyces custersii KCCM 11490 [126], Ethanol red yeast [36] and bacterial strains such as Zymobacter palmae [115] and Escherichia coli SJL2526 [107]. Fermentation of macroalgal polysaccharides is carried out at pH 4.5-6.8 and temperature 25-30 � C and the incubation time is largely strain dependent.…”