CORNELL U N I V E R S I T Y

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Food Science 430 Wine is chemistry, biology and psychology!

Calendar Yield Pathways Slides1 Slides2

Reading: Jackson pp 236-241 Alcoholic Fermentation: Pathways Thomas Henick-Kling Vineyard Site Cultivar Selection Vineyard Management Grape Maturity & Harvest Juice Extraction Alcoholic Fermentation - Pathways Malolactic Fermentation Wine Aging (Storage) fermentation is caused by yeasts and enzymes C6H12O6 + 2 Pi --> 2 C2H5OH +2 CO2 + 2 ATP +heat HISTORY The discovery of yeast as the cause of fermentation. 1632-1723 Antonie van Leeuwenhoek invents the microscope which allows yeast and bacteria to be seen. 1789 Lavoisier: fermentation end products ethanol and CO2 1810 Gay-Lussac: C6H12O6 --> 2 C2H5OH + 2 CO2 1818 Erxleben, De La Tour, Schwann, Kützing (1837): yeasts are the cause 1866 Louis Pasteur: études sur le vin, 1876 études sur la bière Christian Emil Hansen, Hermann Müller-Thurgau, Julius Wortmann (1894) pure culture yeast The discovery of the biochemistry of fermentation 1897 Buchner: extract of yeast retains ability to ferment glucose to ethanol 1905 Harden and Young: heat-labile fraction (zymase, proteins) + heat-stable fraction (cozymase, NAD, ATP, ADP) Gustav Embden: cleavage of fructose 1,6 -di-P Otto Mayerhof: verified Embden's theory and added energetics 1940: Embden-Mayerhof pathway: glucose --> pyruvate also: Otto Warburg, CF Cori and GT Cori, J Parnas many microorganisms can do it, plants (carbonic fermentation) yeasts: Saccharomyces cerevisiae (and other) uptake of sugars passage through cell wall 3 basic entry mechanisms for uptake of solutes (nutrients) across cell membrane: simple diffusion, facilitated (carrier mediated) diffusion, active transport in Saccharomyces crevisiae, glucose, fructose, and mannose are transported via facilitated diffusion, a non-concentrative process, several carriers inside the cell, the sugars are phophorylated S. cerevisiae has 3 glu phosphorylating enzymes: hexokinase PI, hexokinase PII (constitutive), glucokinase sucrose is cleaved outside the cell ---> glucose + fructose ffructofuranidase (=saccharase,=invertase) yeast has an extracellular and intracellular invertase located on the outside of the yeast cell wall glu and fru transported into the cell MULTISTEP REGULATION OF SUGAR FERMENTATION PATHWAY uptake and phosphorylation (hexokinase) phosphofructokinase pyruvate kinase multienzyme complex of glycolytic enzymes uptake of SOLUTES (nutrients) passage through cell wall uptake across cell membrane - 3 basic entry mechanisms: simple diffusion facilitated (carrier mediated) diffusion, active transport UPTAKE OF SUGARS in Saccharomyces crevisiae glucose and fructose are taken up via facilitated diffusion, a non-concentrative process several carriers have specificity for different sugars Looking at the chemistry: C6H12O6 + 6 O2 ---> 6 H2O + 6 CO2 glucose free energy change: delta G = - 686 kcal/mole but for lack of O2 the oxidation of sugars stopps at acetaldehyde C6H12O6 ---> 2 CH3COH + 2 CO2 + 2 NADH2 2 CH3COH + 2 CO2 + 2 NADH2 ---> 2 CH3CH2OH + NAD + 2 CO2 now NAD is regenerated, the breakdown of sugas can start again! Energy released is the difference between the energy of the reactants and the products. 686 kcal ------> (2 x 135) + (2 x 95) = 417 kcal : difference is 227 kcal C6H12O6 ---> 2 CH3CH2OH + 2 CO2 Of the potential 227 kcal, the yeast captures 2 ATP = 2 x 7.5 = 15 kcal  Only 6.6% yield! The Energy gradient is driving the reaction Actually the reaction is a series of flats and cascades: example from Leninger: 2 large drops in delta G several changes with almost no change these reactions can go backwards and forwards but they are coupled and the overall gradient is driving the reaction enzymes are coupled, arranged in sequence so that no intermediate can build up and block the reaction Why does the yeast make ethanol? yeast is actually an aerobic microorganism if it had O2 it would degrade the sugar all the way to CO2 + H2O and would gain 36 ATP but further degradation of acetaldehyde through TCA cycle is blocked yeast cell is left with acetaldehyde and NADH2, dumps H2 on acetaldehyde which is thus turned into ethanol sugar C6H12O6 + 2 Pi + 2 ATP + 2 ADP--> 2 C2H5OH + 2 CO2 + 4 ATP +heat + biomass ethanol

FS430 Revised 2.11.97