Fermentation and Redox Potential

Abstract

Redox potential, known as oxidation-reduction or oxidoreduction potential (ORP), not only indicates the reduction and oxidation capacity of the environment but also reflects the metabolic activity of microorganisms. Redox potential can be monitored online and controlled in time for more efficient fermentation operation. This chapter reviews the enzymes that modulate intracellular redox potential, the genetically engineered strains that harbor specific redox potential-regulated genes, the approaches that were used to manipulate and control redox potential toward the production of desired metabolites, the role of redox potential in metabolic pathway, and the impact of redox potential on microbial physiology and metabolism. The application of redox potential-controlled ethanol fermentation and the development of three redox potential-controlled fermentation processes are illustrated. In the end, the future perspective of redox potential control is provided.

Multifaceted biofuel production by microalgal isolates from Pakistan

“…In darkness, stored starch is converted to pyruvate and ethanol is produced from pyruvate catalyzed by pyruvate decarboxylase and alcohol dehydrogenase. Under the prevalent dark, anaerobic conditions, fermentation pathways are upregulated to allow the cell to generate reductants for carrying basal cellular activity in the absence of repressed photosynthetic machinery …”

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

“…The synthesis of these classes of compounds prepares the yeasts for successive rounds of division and helps to fortify the plasma membrane against proton stress and the dehydrating effects of alcohol [ 49 ]. Actively dividing yeast also decreases the redox potential by excreting reductive compounds (e.g., glutathione, protons) [ 21 ]. Previous work has shown that as a yeast population reaches an “ORP Minimum”, the biological and extracellular chemical production of H 2 S spikes, causing the yeast population to undergo a physiological transition from exponential growth phase into stationary phase [ 18 , 23 ].…”

“…Previous work has demonstrated the effectiveness of using ORP as a strategy for controlling the activity of biological systems [ 15 ]. In low-oxygen yeast fermentations, changes in redox potential are primarily driven by the physiological and metabolic status of the yeast population: as yeast depletes molecular O 2 , produces CO 2 , and excretes reductive metabolites, it causes the ORP to decrease [ 21 ]. As fermentation progresses, an “ORP minimum” is reached, which corresponds with an increase in hydrogen sulfide (H 2 S) due to yeast amino acid metabolism and spontaneous extracellular reduction of elemental sulfur at low redox potential [ 18 , 20 , 22 ].…”

Platform molecule from sustainable raw materials; case study succinic acid

“…Although many fermentation processes have been well developed with long-term operability, cost saving is an endless effort, particularly for biofuels and bio-based chemicals production at bulk quantity such as ethanol and butanol to address global concern on sustainable development (Kracke et al 2018). Since redox reactions and homeostasis are basis for intracellular metabolism, ORP status controls metabolites profiles, which subsequently offers a strategy to direct the pathway for efficient production of more and more materials and energy (Liu et al 2017a). With advanced technologies that can detect ORP levels and its intracellular influence on gene expression, protein biosynthesis and metabolites caused by ORP shifts, mechanism underlying this phenomenon can be elucidated.…”

“…More robust strains and optimized processes can be developed by redox potential which can be controlled by metabolic modifications and bioprocess engineering levels, which have been highlighted in ethanol and butanol fermentations under microaerobic and anaerobic conditions (Liu et al 2017a). Figure 3 shows the standard ORP of some redox pairs in an intracellular metabolism and it is affected by temperature, aerobic or anaerobic conditions.…”