Optimization of low-cost medium for very high gravity ethanol fermentations by Saccharomyces cerevisiae using statistical experimental designs

Abstract

Statistical experimental designs were used to develop a medium based on corn steep liquor (CSL) and other low-cost nutrient sources for high-performance very high gravity (VHG) ethanol fermentations by Saccharomyces cerevisiae. The critical nutrients were initially selected according to a Plackett-Burman design and the optimized medium composition (44.3 g/L CSL; 2.3 g/L urea; 3.8 g/L MgSO₄·7H₂O; 0.03 g/L CuSO₄·5H₂O) for maximum ethanol production by the laboratory strain CEN.PK 113-7D was obtained by response surface methodology, based on a three-level four-factor Box-Behnken design. The optimization process resulted in significantly enhanced final ethanol titre, productivity and yeast viability in batch VHG fermentations (up to 330 g/L glucose) with CEN.PK113-7D and with industrial strain PE-2, which is used for bio-ethanol production in Brazil. Strain PE-2 was able to produce 18.6±0.5% (v/v) ethanol with a corresponding productivity of 2.4±0.1g/L/h. This study provides valuable insights into cost-effective nutritional supplementation of industrial fuel ethanol VHG fermentations.

Optimization of Corn Steep Liquor Dosage and Other Fermentation Parameters for Ethanol Production by Saccharomyces cerevisiae Type 1 and Anchor Instant Yeast

“…Type of Yeast Ethanol (g/L) Yield (%) CSL (% w/v) Scale Author [22] However, the fact that this method does not account for the interactive effects which may exist among the variables puts the reliability of such optimum conditions in doubt, especially if large-scale production is envisaged [23]. The interactive effect among the fermentation parameters can be ascertained through the use of effective optimization tools.…”

“…In addition to analyzing the effects of the independent variables, this method also generates a mathematical expression that describes the relationship between variables and a selected response [25]. Pereira et al [22] used a Placket-Burman design to initially select the critical nutrients for CSL and other low-cost nutrients for ethanol fermentation, followed by a Box-Behnken design for the optimization of the selected nutrients [22]. It is clear, however, that most of the critical nutrients selected for optimization may be redundant, as they are already contained in adequate quantities in CSL [26]; eliminating them may significantly improve the economics of the process, especially on an industrial scale.…”

“…It is clear, however, that most of the critical nutrients selected for optimization may be redundant, as they are already contained in adequate quantities in CSL [26]; eliminating them may significantly improve the economics of the process, especially on an industrial scale. While the applicability of RSM to optimization studies has been demonstrated successfully [22,25,27], studies have also shown that its predictive capability may be limited [24,28]. Baş and Boyacı [24] reported that the second-order equation obtained from RSM did not show the interactive effects of pH and substrate concentration on the initial reaction rate of the enzymatic reaction in their study.…”

“…Dry yeast, Anchor Instant Yeast, a product of Rymco (Pty) Ltd (Maraisburg Rd, South Africa), 22 Bunsen Street, Industria, South Africa, and a yeast product from Sigma Aldrich (St. Louis, MO, USA) called Saccharomyces Type 1 (Baker's yeast) were purchased for the study. The activation of the baker's instant dry yeast was done by adding a spatula of the yeast to 150 mL distilled water in a 250 mL Duran flask and placing it on a shaking platform incubator (Labcon FSIM SP016, Zenfer manufacture Services CC., Maraisburg, South Africa) for 18 h [34].…”

A Simple Method to Determine Bioethanol Production from Coffee Mucilage, Verified by HPLC

“…Viable cell counts were measured with a Neubauer chamber adapted with optical microscopy (Pereira et al 2010), and trypan blue dye was used on the vital cells (Tolnai 1975). Bioethanol concentration was determined with a pycnometer method through densities verified with HPLC, using a column (Phenomenex, Inc. USA) eluted at 60 °C with 0.0025 M H2SO4 at a flow rate of 0.5 mL/min and having a refractiveindex detector.…”