Kinetic and Energetic Parameters of Carob Wastes Fermentation by Saccharomyces cerevisiae: Crabtree Effect, Ethanol Toxicity, and Invertase Repression
1
조회
0
다운로드
2
인용
0
참고문헌
키워드
초록
Carob waste is a useful raw material for the second-generation ethanol because 50% of its dry weight is sucrose, glucose, and fructose. To optimize the process, we have studied the influence of the initial concentration of sugars on the fermentation performance of Saccharomyces cerevisiae. With initial sugar concentrations (S0) of 20 g/l, the yeasts were derepressed and the ethanol produced during the exponential phase was consumed in a diauxic phase. The rate of ethanol consumption decreased with increasing S0 and disappeared at 250 g/l when the Crabtree effect was complete and almost all the sugar consumed was transformed into ethanol with a yield factor of 0.42 g/g. Sucrose hydrolysis was delayed at high S0 because of glucose repression of invertase synthesis, which was triggered at concentrations above 40 g/l. At S0 higher than 250 g/l, even when glucose had been exhausted, sucrose was hydrolyzed very slowly, probably due to an inhibition at this low water activity. Although with lower metabolic rates and longer times of fermentation, 250 g/l is considered the optimal initial concentration because it avoids the diauxic consumption of ethanol and maintains enough invertase activity to consume all the sucrose, and also avoids the inhibitions due to lower water activities at higher S0.
Abstract
Carob waste is a useful raw material for the second-generation ethanol because 50% of its dry weight is sucrose, glucose, and fructose. To optimize the process, we have studied the influence of the initial concentration of sugars on the fermentation performance of Saccharomyces cerevisiae. With initial sugar concentrations (S0) of 20 g/l, the yeasts were derepressed and the ethanol produced during the exponential phase was consumed in a diauxic phase. The rate of ethanol consumption decreased with increasing S0 and disappeared at 250 g/l when the Crabtree effect was complete and almost all the sugar consumed was transformed into ethanol with a yield factor of 0.42 g/g. Sucrose hydrolysis was delayed at high S0 because of glucose repression of invertase synthesis, which was triggered at concentrations above 40 g/l. At S0 higher than 250 g/l, even when glucose had been exhausted, sucrose was hydrolyzed very slowly, probably due to an inhibition at this low water activity. Although with lower metabolic rates and longer times of fermentation, 250 g/l is considered the optimal initial concentration because it avoids the diauxic consumption of ethanol and maintains enough invertase activity to consume all the sucrose, and also avoids the inhibitions due to lower water activities at higher S0.
참고문헌 (19)
- Avallone R, "Determination of chemical composition of carob (Ceratonia siliqua): protein, fat, carbohydrates and tannins", J. Food Compost. Anal, 10, pp.166~172 (1997)
- Baranyi J, "A dynamic approach to predicting bacterial growth in food", Int. J. Food Microbiol, 23, pp.277~294 (1994)
- Brown SW, "Ethanol inhibition of yeast growth and fermentation: differences in the magnitude and complexity of the effect", Eur. J. Appl. Microbiol. Biotechnol, 11, pp.151~155 (1981)
- Cazetta ML, "Fermentation of molasses by Zymomonas mobilis: effects of temperature and sugar concentration on ethanol production", Bioresour. Technol, 98, pp.2824~2828 (2007)
- Forbes C, "Application of high rate, high temperature anaerobic digestion to fungal thermozyme hydrolysates from carbohydrate wastes", Water Res, 43, pp.2531~2539 (2009)
- Lima-Costa ME, "Kinetics of sugars consumption and ethanol inhibition in carob pulp fermentation by Saccharomyces cerevisiae in batch and fed-batch cultures", J. Ind. Microbiol. Biotechnol, 39, pp.789~797 (2012)
- Meijer MM, "Glucose repression in Saccharomyces cerevisiae is related to the glucose concentration rather than the glucose flux", J. Biol. Chem, 273, pp.24102~24107 (1998)
- Mishra J, "A comparative study of ethanol production from various agro residues by using Saccharomyces cerevisiae and Candida albicans", J. Yeast Fungal Res, 3, pp.12~17 (2012)
- Mormeneo S, "Regulation of invertase synthesis by glucose in Saccharomyces cerevisiae", Fed. Eur. Biochem. Soc. J, 152, pp.14~18 (1982)
- Mussato SI, "Technological trends, global market, and challenges of bio-ethanol production", Biotechnol. Adv, 28, pp.817~830 (2010)
- Raamsdonk LM, "Co-consumption of sugars or ethanol and glucose in a Saccharomyces cerevisiae strain deleted in the HXK2 gene", Yeast, 18, pp.1023~1033 (2001)
- Raposo S, "Kinetic modelling of bioethanol production using agro-industrial by-products", Int. J. Energy Environ, 3, pp.1~8 (2009)
- Santo DE, "Yeast diversity in the Mediterranean strawberry tree (Arbutus unedo L.)fruits’ fermentations", Food Res. Int, 47, pp.45~50 (2012)
- Santos J, "Ethanol tolerance of sugar transport, and the rectification of stuck wine fermentations", Microbiology, 154, pp.422~430 (2008)
- Santos M, "Production of dextran and fructose from carob extract and cheese whey by Leuconostoc mesenteroides NRRL B512(f)", Biochem. Eng. J, 25, pp.1~6 (2005)
- Takeshige K, "Effects of yeast invertase on ethanol production in molasses", J. Ferment. Bioeng, 79, pp.513~515 (1995)
- Thongchul N, "Production of lactic acid and ethanol by Rhizopus oryzae integrated with cassava pulp hydrolysis", Bioprocess Biosyst. Eng, 33, pp.407~416 (2010)
- Vaheed H, "Evaluation and optimization of ethanol production from carob pod extract by Zymomonas mobilis using response surface methodology", J. Ind. Microbiol. Biotechnol, 38, pp.101~111 (2011)
- Zhao XQ, "Mechanisms of yeast stress tolerance and its manipulation for efficient fuel ethanol production", J. Biotechnol, 144, pp.23~30 (2009)