Redox potential driven aeration during very-high-gravity ethanol fermentation by using flocculating yeast

Manipulating Microbial Cell Morphology for the Sustainable Production of Biopolymers

The total rate of plastic production is anticipated to surpass 1.1 billion tons per year by 2050. Plastic waste is non-biodegradable and accumulates in natural ecosystems. In 2020, the total amount of plastic waste was estimated to be 367 million metric tons, leading to unmanageable waste disposal and environmental pollution issues. Plastics are produced from petroleum and natural gases. Given the limited fossil fuel reserves and the need to circumvent pollution problems, the focus has shifted to biodegradable biopolymers, such as polyhydroxyalkanoates (PHAs), polylactic acid, and polycaprolactone. PHAs are gaining importance because diverse bacteria can produce them as intracellular inclusion bodies using biowastes as feed. A critical component in PHA production is the downstream processing procedures of recovery and purification. In this review, different bioengineering approaches targeted at modifying the cell morphology and synchronizing cell lysis with the biosynthetic cycle are presented for product separation and extraction. Complementing genetic engineering strategies with conventional downstream processes, these approaches are expected to produce PHA sustainably.

Monitoring Site-Specific Fermentation Outcomes via Oxidation Reduction Potential and UV-Vis Spectroscopy to Characterize "Hidden" Parameters of Pinot Noir Wine Fermentations

Real-time process metrics are standard for the majority of fermentation-based industries but have not been widely adopted by the wine industry. In this study, replicate fermentations were conducted with temperature as the main process parameter and assessed via in-line Oxidation Reduction Potential (ORP) probes and at-line profiling of phenolics compounds by UV-Vis spectroscopy. The California and Oregon vineyards used in this study displayed consistent vinification outcomes over five vintages and are representative of sites producing faster- and slower-fermenting musts. The selected sites have been previously characterized by fermentation kinetics, elemental profile, phenolics, and sensory analysis. ORP probes were integrated into individual fermentors to record how ORP changed throughout the fermentation process. The ORP profiles generally followed expected trends with deviations revealing previously undetectable process differences between sites and replicates. Site-specific differences were also observed in phenolic and anthocyanin extraction. Elemental composition was also analyzed for each vineyard, revealing distinctive profiles that correlated with the fermentation kinetics and may influence the redox status of these wines. The rapid ORP responses observed related to winemaking decisions and yeast activity suggest ORP is a useful process parameter that should be tracked in addition to Brix, temperature, and phenolics extraction for monitoring fermentations.

Machine learning applied for metabolic flux-based control of micro-aerated fermentations in bioreactors

Various bio-based processes depend on controlled micro-aerobic conditions to achieve a satisfactory product yield. However, the limiting oxygen concentration varies according to the micro-organism employed, while for industrial applications, there is no cost-effective way of measuring it at low levels. This study proposes a machine learning procedure within a metabolic flux-based control strategy (SUPERSYS_MCU) to address this issue. The control strategy used simulations of a genome-scale metabolic model to generate a surrogate model in the form of an artificial neural network, to be used in a micro-aerobic fermentation strategy (MF-ANN). The meta-model provided setpoints to the controller, allowing adjustment of the inlet air flow to control the oxygen uptake rate. The strategy was evaluated in micro-aerobic batch cultures employing industrial Saccharomyces cerevisiae yeast, with defined medium and glucose as the carbon source, as a case study. The performance of the proposed control scheme was compared with a conventional fermentation and with three previously reported micro-aeration strategies, including respiratory quotient-based control and constant air flow rate. Due to maintenance of the oxidative balance at the anaerobiosis threshold, the MF-ANN provided volumetric ethanol productivity of 4.16 g·L^-1 ·h^-1 and a yield of 0.48 g_ethanol .g_substrate ^-1 , which were higher than the values achieved for the other conditions studied (maximum of 3.4 g·L^-1 ·h^-1 and 0.35-0.40 g_ethanol ·g_substrate ^-1 , respectively). Due to its modular character, the MF-ANN strategy could be adapted to other micro-aerated bioprocesses.

High Gravity and Very High Gravity Fermentation of Sugarcane Molasses by Flocculating Saccharomyces cerevisiae: Experimental Investigation and Kinetic Modeling

Substantial progress has been made in ethanol fermentation technology under high gravity (HG) and very high gravity (VHG), which offer environmental and economic benefits. HG and VHG processes increase the productivity of ethanol, reduce distillation costs, and enable higher yields. The aim of the present study was to evaluate the use of sugarcane molasses as the medium component along with flocculating yeasts for fermentation in a fed-batch process employing this promising technology. We evaluated fed-batch fermentation, HG, and VHG involving a molasses-based medium with high concentrations of reducing sugars (209, 222, and 250 g/L). Fermentation of 222 g/L of total reducing sugars achieved 89.45% efficiency, with a final ethanol concentration of 104.4 g/L, whereas the highest productivity (2.98 g/(L.h)) was achieved with the fermentation of 209 g/L of total reducing sugars. The ethanol concentration achieved with the fermentation of 222 g/L of total reducing sugars was close to the value obtained for P'_max (105.35 g/L). The kinetic model provided a good fit to the experimental data regarding the fermentation of 222 g/L. The results revealed that sugarcane molasses and flocculating yeasts can be efficiently used in HG fermentation to reduce the costs of the process and achieve high ethanol titers.

A microbubble-sparged yeast propagation-fermentation process for bioethanol production

BACKGROUND

Industrial biotechnology will play an increasing role in creating a more sustainable global economy. For conventional aerobic bioprocesses supplying O₂ can account for 15% of total production costs. Microbubbles (MBs) are micron-sized bubbles that are widely used in industry and medical imaging. Using a fluidic oscillator to generate energy-efficient MBs has the potential to decrease the costs associated with aeration. However, little is understood about the effect of MBs on microbial physiology. To address this gap, a laboratory-scale MB-based Saccharomyces cerevisiae Ethanol Red propagation-fermentation bioethanol process was developed and analysed.

RESULTS

Aeration with MBs increased O₂ transfer to the propagation cultures. Titres and yields of bioethanol in subsequent anaerobic fermentations were comparable for MB-propagated and conventional, regular bubble (RB)-propagated yeast. However, transcript profiling showed significant changes in gene expression in the MB-propagated yeast compared to those propagated using RB. These changes included up-regulation of genes required for ergosterol biosynthesis. Ergosterol contributes to ethanol tolerance, and so the performance of MB-propagated yeast in fed-batch fermentations sparged with 1% O₂ as either RBs or MBs were tested. The MB-sparged yeast retained higher levels of ergosteryl esters during the fermentation phase, but this did not result in enhanced viability or ethanol production compared to ungassed or RB-sparged fermentations.

CONCLUSIONS

The performance of yeast propagated using energy-efficient MB technology in bioethanol fermentations is comparable to that of those propagated conventionally. This should underpin the future development of MB-based commercial yeast propagation.

Production of ethanol from Jerusalem artichoke by mycelial pellets

Mycelial pellets formed by Aspergillus niger A-15 were used to immobilize the ethanol producing yeast Saccharomyces cerevisiae C-15. The operation parameters, such as agitation speed, temperature and mixed proportion of strains were studied. The optimal adsorption 66.9% was obtained when speed was 80r/min, temperature was 40 °C and mixed proportion(mycelial pellets: yeasts) was 1:10. With Jerusalem artichoke flour as substrate, 12.8% (V/V) of ethanol was obtained after 48 h by simultaneous saccharification and fermentation using mycelial pellets. And mycelial pellets could tolerate 19% (volume fraction) ethanol. The above results proved that this new technology was feasible, and it had the advantages of higher ethanol yield, long service life, repeated use, easy operation and lower cost in producing ethanol.

Integrated Process for Bioenergy Production and Water Recycling in the Dairy Industry: Selection of Kluyveromyces Strains for Direct Conversion of Concentrated Lactose-Rich Streams into Bioethanol

Dairy industries have a high environmental impact, with very high energy and water consumption and polluting effluents. To increase the sustainability of these industries it is urgent to implement technologies for wastewater treatment allowing water recycling and energy savings. In this study, dairy wastewater was processed by ultrafiltration and nanofiltration or ultrafiltration and reverse osmosis (UF/RO) and retentates from the second membrane separation processes were assessed for bioenergy production. Lactose-fermenting yeasts were tested in direct conversion of the retentates (lactose-rich streams) into bioethanol. Two Kluyveromyces strains efficiently fermented all the lactose, with ethanol yields higher than 90% (>0.47 g/g yield). Under severe oxygen-limiting conditions, the K. marxianus PYCC 3286 strain reached 70 g/L of ethanol, which is compatible with energy-efficient distillation processes. In turn, the RO permeate is suitable for recycling into the cleaning process. The proposed integrated process, using UF/RO membrane technology, could allow water recycling (RO permeate) and bioenergy production (from RO retentate) for a more sustainable dairy industry.

Multivariate analysis of metabolic parameters and optimization of antibody production using high cell density hybridoma in hollow fiber bioreactors

OBJECTIVES

The relationships of manipulation of culture temperature and medium circulation rate on the metabolic parameters were regressed by multiple linear regression analysis in hollow fiber bioreactors (HFB).

RESULTS

The high circulation rate could significantly enhance the oxygen consumption of the hybridoma cells and the medium's oxidation-reduction potential. A mildly hypothermic condition of 36 °C and a circulation rate of 182.5 mL/min could support the hybridoma had the maximal antibody titer of 60.75 μg/mL for 20 days. When the ammonium ion was 65 ppm or lactate close to 2.6 g/L, the medium was replaced to maintain the stable and healthy cells at the high cell concentration of 3.33 × 10⁸/mL for continuous antibody production. Two serum-free media could be successfully applied to this perfusion system and maintain hybridoma growth and antibody production.

CONCLUSION

The single-use HFBs could provide the advantages including high cell density, low shear stress, and continuous antibody production.

Enhancement of ethanol production in very high gravity fermentation by reducing fermentation-induced oxidative stress in Saccharomyces cerevisiae

During fermentation, yeast cells encounter a number of stresses, including hyperosmolarity, high ethanol concentration, and high temperature. Previous deletome analysis in the yeast Saccharomyces cerevisiae has revealed that SOD1 gene encoding cytosolic Cu/Zn-superoxide dismutase (SOD), a major antioxidant enzyme, was required for tolerances to not only oxidative stress but also other stresses present during fermentation such as osmotic, ethanol, and heat stresses. It is therefore possible that these fermentation-associated stresses may also induce endogenous oxidative stress. In this study, we show that osmotic, ethanol, and heat stresses promoted generation of intracellular reactive oxygen species (ROS) such as superoxide anion in the cytosol through a mitochondria-independent mechanism. Consistent with this finding, cytosolic Cu/Zn-SOD, but not mitochondrial Mn-SOD, was required for protection against oxidative stress induced by these fermentation-associated stresses. Furthermore, supplementation of ROS scavengers such as N-acetyl-L-cysteine (NAC) alleviated oxidative stress induced during very high gravity (VHG) fermentation and enhanced fermentation performance at both normal and high temperatures. In addition, NAC also plays an important role in maintaining the Cu/Zn-SOD activity during VHG fermentation. These findings suggest the potential role of ROS scavengers for application in industrial-scale VHG ethanol fermentation.

The establishment of a marine focused biorefinery for bioethanol production using seawater and a novel marine yeast strain

Current technologies for bioethanol production rely on the use of freshwater for preparing the fermentation media and use yeasts of a terrestrial origin. Life cycle assessment has suggested that between 1,388 to 9,812 litres of freshwater are consumed for every litre of bioethanol produced. Hence, bioethanol is considered a product with a high-water footprint. This paper investigated the use of seawater-based media and a novel marine yeast strain ‘Saccharomyces cerevisiae AZ65’ to reduce the water footprint of bioethanol. Results revealed that S. cerevisiae AZ65 had a significantly higher osmotic tolerance when compared with the terrestrial reference strain. Using 15-L bioreactors, S. cerevisiae AZ65 produced 93.50 g/L ethanol with a yield of 83.33% (of the theoretical yield) and a maximum productivity of 2.49 g/L/h when using seawater-YPD media. This approach was successfully applied using an industrial fermentation substrate (sugarcane molasses). S. cerevisiae AZ65 produced 52.23 g/L ethanol using molasses media prepared in seawater with a yield of 73.80% (of the theoretical yield) and a maximum productivity of 1.43 g/L/h. These results demonstrated that seawater can substitute freshwater for bioethanol production without compromising production efficiency. Results also revealed that marine yeast is a potential candidate for use in the bioethanol industry especially when using seawater or high salt based fermentation media.