title: Kinetic and Energetic Parameters of Carob Wastes Fermentation by Saccharomyces cerevisiae: Crabtree Effect, Ethanol Toxicity, and Invertase Repression.
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.
authors.affiliation: Centre for Marine and Environmental Research, CIMA, Faculty of Sciences and Technology, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: B
authors.initials: B
authors.lastname: Rodrigues
authors.affiliation: Faculty of Biology, Department of Microbiology III, Universidad Complutense, 28040 Madrid, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Peinado
authors.affiliation: Centre for Marine and Environmental Research, CIMA, Faculty of Sciences and Technology, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: S
authors.initials: S
authors.lastname: Raposo
authors.affiliation: Centre for Marine and Environmental Research, CIMA, Faculty of Sciences and Technology, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: A
authors.initials: A
authors.lastname: Constantino
authors.affiliation: Institute of Engineering, University of Algarve, 8005-139 Faro, Portugal.
authors.forename: C
authors.initials: C
authors.lastname: Quintas
authors.affiliation: Centre for Marine and Environmental Research, CIMA, Faculty of Sciences and Technology, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: M E
authors.initials: ME
authors.lastname: Lima-Costa
mesh_terms: D000431:Ethanol / Q000378:metabolism* / Q000633:toxicity*; D005285:Fermentation; D005685:Galactans / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D007220:Industrial Waste; D008351:Mannans / Q000378:metabolism*; D053149:Plant Gums / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000378:metabolism*; D043324:beta-Fructofuranosidase / Q000378:metabolism
chemical_list: D005685:Galactans; D007220:Industrial Waste; D008351:Mannans; D053149:Plant Gums; D000431:Ethanol; D043324:beta-Fructofuranosidase; C017471:locust bean gum