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FELC Discussion Group November 12, 2013

FELC Discussion Group November 12, 2013. Effects of Short Chain Fatty Acids on Yeast Metabolism Moderators: Courtney Ireland (Corn Plus) & Asfia Qureshi Ph.D. (Verenium). FELC Discussion Group Nov 2013 Discussion Norms. Please speak kindly and professionally to each other

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FELC Discussion Group November 12, 2013

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  1. FELC Discussion Group November 12, 2013 Effects of Short Chain Fatty Acids on Yeast Metabolism Moderators: Courtney Ireland (Corn Plus) & Asfia Qureshi Ph.D. (Verenium)

  2. FELC Discussion Group Nov 2013Discussion Norms • Please speak kindly and professionally to each other • Everyone is welcome to offer ideas and suggestions to the topic • Do not belittle each other • Learn from each other

  3. Short Chain Fatty Acids are C1-C5 • What is a short chain fatty acid (SCFA)? • Usually C1-C5 • Includes formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid • Have individual pKa values to indicate what proportion is in the dissociated (COO-) and undissociated (COOH) form at any pH.

  4. Short Chain Fatty Acids Have Specific pKas • In alkaline media (pH >7) COO- form will be prominent

  5. Short Chain Fatty Acids Interfere in Yeast Metabolism • Why are SCFA relevant? • Seminal paper from 60 years ago describes the effects of acetate and other short chain fatty acids on yeast metabolism • During early phases of glucose fermentation, phosphate is taken up by starved, mature yeast cells. • Phosphate accumulation (and thus yeast growthand fermentation) is inhibited by C2, C4, C8 (concentration and pH dependent)

  6. Effects of Short Chain Fatty Acids on Yeast Metabolism • Short chain fatty acids influence the fermentative activity of yeast cells • High concentrations inhibit • Low concentrations enhance • Increasing chain length of fatty acid increases inhibitory action • What are the actions of fatty acids? • Bactericidal activity • Inhibit growth rate • “Glycogen sparring” action in yeast cells

  7. A pH Increase Can Circumvent Their Effects • How do they work? • By binding to enzymes and other proteins in the cell membrane • How to overcome this? • If SCFA are coming out of methanator, increase the pH at prop and ferm – this will shift FA to their dissociated forms which cannot enter yeast cell to cause inhibition • Wash the cells/mash (hexane/ether extraction will remove FA – then analyze by GC)

  8. SCFAs are Connected to Fusel Oil Inhibition • SCFA inhibition is connected to fusel inhibition in yeasts • Fusel oils are • By-products of ethanol production process • mix of volatile organic acids, higher alcohols, aldehydes, ketones, fatty acids, esters • toxic to yeast growth and fermentation • usually removed using a rectifier distillation column

  9. FELC Discussion Group Nov 2013 Thank you for a great discussion!

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