Repeated cultures of Saccharomyces cerevisiae SC90 to tolerate inhibitors generated during cassava processing waste hydrolysis for bioethanol production
Large amount of cassava pulp is produced as by-product of industrial tapioca production. The value-added process of this low-cost waste is to use it as a substrate for bioethanol production. However, during the pulp pretreatment by acidification combined with steam explosion, many yeast inhibitors including acetic acid, formic acid, levulinic acid, furfural and 5-hydroxymethylfurfural are generated and these compounds have negative effects on the subsequent fermentation step. Therefore, the objective of this study was to investigate whether the repeated cultures of Saccharomyces cerevisiae SC90 could alleviate this problem. To obtain the inhibitor tolerable cells, the repeated culture was performed by growing yeast cells to a specific growth rate (µ) of 0.22 h−1 or higher (80% of the µ in control) and then transferring them to progressively higher concentrations of hydrolysate ranging from 20 to 100% (v/v). The results showed a tendency of longer lag phase as well as time to reach maximum cell number (tmaxc) with an increase in hydrolysate concentration. However, the repeated culture at the same hydrolysate concentration could shorten both lag period and tmaxc. Interestingly, the growth and fermentation efficiency of adapted cells in 100% hydrolysate were significantly higher (p ≤ 0.05) than those of non-adapted cells by 38% and 27%, respectively.
KeywordsAdaptation Cassava pulp Inhibitors Inhibitor tolerance Saccharomyces cerevisiae
This research was financially supported by King Mongkut’s Institute of Technology Ladkrabang (KMITL) (A118-59-070) and National Research Council of Thailand. The contribution of Prof. Dr. Anthony Keith Thompson and Prof. Dr. George Srzednicki (visiting Professor at Faculty of Agro-Industry, KMITL) for critically editing the manuscript is acknowledged.
PPNA: literature review, design of the research outline, design of research tools, analysis of data, interpretation of the data analysis, and drafting of the article (first draft). TC: design of the research outline, design of research tools, decision on the data analysis method, interpretation of the data analysis, revision of the draft of the article (second draft), and final approval of the article (final draft). WK: conception of the project, design of the research outline, interpretation of the data analysis, and final approval of the article (final draft). SP: conception of the project, literature review, design of the research outline, design of research tools, decision on the data analysis method, analysis of data, interpretation of the data analysis, revision of the draft of the article (second draft), and final approval of the article (final draft).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- El-Mansi EMT, Bruce Ward F (2006) Microbiology of industrial fermentation. In: El-Mansi EMT, Bryce CFA, Demain AL, Allman AR (eds) Fermentation microbiology and biotechnology, 2nd edn. Taylor & Francis, Boca Raton, pp 11–46Google Scholar
- Greetham D (2014) Presence of low concentrations of acetic acid improves fermentations using Saccharomyces cerevisiae. J Bioprocess Biotech 5:192Google Scholar
- Lane J (2017) Thailand announces $11.3 billion 10-year plan to build sugarcane and cassava bioeconomy. Biofuelsdigest. http://www.biofuelsdigest.com/bdigest/2017/01/25/thailand-announces-11-3-billion-10-year-plan-to-build-sugarcane-and-cassava-bioeconomy-2. Accessed 26 Nov 2018
- Pornpukdeewattana S, Khamfun J, Phatyenchai N (2014) Adaptation of commercial yeast Saccharomyces cerevisiae SC90 to tolerate inhibitors generated during cassava pulp hydrolysis. Suranaree J Sci Technol 21:335–345Google Scholar
- Sluiter A, Hames B, Ruiz R, Scarlata C, Sluiter J, Templeton D, Crocker D (2012) Determination of structural carbohydrates and lignin in biomass, laboratory analytical procedure (LAP). National Renewable Energy Laboratory (NREL) Web. https://www.nrel.gov. Accessed 17 Jan 2019
- Smart KA, Chambers KM, Lambert I, Jenkins C (1999) Use of methylene violet staining procedures to determine yeast viability and vitality. J Am Soc Brew Chem 57:18–23Google Scholar
- Srinorakutara T, Kaewvimol L, Saengow L (2006) Approach of cassava waste pretreatments for fuel ethanol production in Thailand. J Sci Res Chula Univ 31:77–84Google Scholar
- Zhu JJ, Yong Q, Xu Y, Chen SX, Yu SY (2009) Adaptation fermentation of Pichia stipitis and combination detoxification on steam exploded lignocellulosic prehydrolyzate. Nat Sci 1:47–54Google Scholar