Production of organically bound selenium yeast by continuous fermentation

Area of Science:

• Biotechnology
• Microbiology
• Biochemistry

Background:

• Saccharomyces cerevisiae is a widely used yeast for biomass production.
• Incorporating selenium into yeast biomass can enhance its nutritional value.
• Optimizing selenium incorporation requires careful control of fermentation conditions and selenium source.

Purpose of the Study:

• To describe a protocol for incorporating sodium selenite or sodium selenate into Saccharomyces cerevisiae biomass.
• To investigate the effects of different selenium sources and concentrations on selenium incorporation and speciation.
• To determine optimal conditions for the continuous production of organically bound selenium in yeast biomass.

Main Methods:

• Continuous fermentation of Saccharomyces cerevisiae at a 0.2 h(-1) dilution rate.
• Addition of sodium selenite (Na(2)SeO(3)) or sodium selenate (Na(2)SeO(4)) to the fermentation medium with minimal sulfur and methionine.
• Analysis of selenium incorporation using atomic absorption analysis and methylene blue reduction time (MBRT) to differentiate between inorganic and organic selenium.

Main Results:

• Sodium selenite addition yielded high biomass with predominantly inorganic selenium (MBRT = 0.1 min).
• Sodium selenate addition resulted in lower biomass but a higher proportion of organically bound selenium (MBRT = 26 min).
• Optimal Se/S ratio of 3.9:1 and dry biomass/Se ratio of 5.5:1 were identified for producing organically bound selenium.

Conclusions:

• Continuous fermentation with sodium selenate is effective for producing yeast biomass enriched with organically bound selenium.
• The methylene blue reduction time (MBRT) is a useful indicator for assessing the form of selenium incorporated into yeast biomass.
• Specific selenium-to-sulfur and biomass-to-selenium ratios are crucial for maximizing the production of organically bound selenium in yeast.