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Fermentation
| Alcoholic fermentation | Is the anaerobic transformation of sugars, mainly glucose and fructose, into ethanol and carbon dioxide. This is process, which is carried out by yeast and also by some bacteria such as Zymomonas mobilis, can summarised by this overall reaction. |
| C6H12O6-> | 2CH3CH2OH+ 2CO2 |
| besides ethanol, several other compounds are produced through alcohol fermentation such as | higher alchols, esters, glycerol, succinic acid, diacetyal, acetoin and 2,3-butanediol. Simultaneously, some compounds of grape juice are also transformed by by yeast metabolism. |
| Biodiversity in yeast depends on several factors | such as -grape variety, -the ripening stage at harvest, -the anitfungal treatments, -the climatic conditions of the year, -the development of grey rot or other fungal plagues -and the viticultural practices. |
| different yeast species participate in spontaneous alcoholic fermentation even | when sulphur dioxide is present, |
| what yeasts participate in early stages of fermentation? | Kloeckera, Hanseniaspora, and Candida |
| what yeast participate in middle stages of alcoholic fermentation? | Pichia and Metschnikowia |
| what yeast participate in the latter stage of fermentation? | Saccharomyces ceravisiae = predominant yeast because of its greater resistence to high ethanol concentration |
| other yeasts that may be present in alcoholic fermentation that cause organoleptic defects | -Torulaspora -Kluyveromyces -Schizosacchamyces -Zygosaccharomyces Brettanomyces |
| What do wineries add to prevent undesirable yeasts from developing? | Sulphur dioxide and inoculate selected strains of dry yeasts -Saccharomyces cerevisiae. |
| At beginning of the winemaking process, the yeast will metabolize the sugars and other nutrients, what do the yeasts use the nutrients for? | obtain energy and increase their population. |
| Latency Phase fermentation -initial population depends on several factors | -no yeast are inoculated population is around 10.4 -selected yeasts are inoculated initial population would be higher |
| exponential growth phase -once yeasts have adapted to the environmental conditions they begin to grow -will increase population -3-6days and after that yeasts stop growing because they become nutrient deficient | -highly influenced by temperature -concentration of ammonia -amino acids and other nutrients -presence of oxygen |
| quasi-stationary phase | -the population of yeasts remains nearly stable -can last from 2-10 days |
| decline phase | -population of yeasts decreases gradually until almost completely disappeared -will die because of lack of nutrients and also because ethanol and other substances are produced during alcoholic fermentation are toxic to them |
| the success of an alcoholic depends on | maintaining the population of viable yeast at sufficient levels until all the fermentable sugars have been fully consumed -otherwise the winemaker is faced with problem of stuck and sluggish fermentations |
| Glycolysis | process consists of the intracellular transformation of glucose and fructose into pyruvate. This biochemical pathway is the initial process of carbohydrate catabolism in most organisms and it takes place completely within the cytoplasm. |
| what does yeasts use as the main pathway for sugar catabolism? | glycolysis |
| yeasts can consume sugar using what two different pathways? | respiration and fermentation |
| respiration and fermentation produce what as a final product after beginning with glycolysis? | generates pyruvate |
| what is pyruvate turned into? | ethanol and carbon dioxide by the enzyme pyruvate decarboxylase |
| where does alcoholic fermentation take place? | within the cytoplasm |
| alcoholic fermentation regenerates what? | NAD+ consumed during glycolysis and gives yeasts an energy gain of only two ATP molecules by metabolized hexose. |
| what transforms pyruvate into acetyl-coA and carbon dioxide? | pyruvate dehydrogenase -also reaction reduces NAD+ to NADH -incorporate the coenzyme A |
| What cycle is Acetyl-CoA incorporated into and transformed into carbon dioxide producing several molecules of reduced coenzymes NADH and FADH2. | Krebs Cycle |
| process known as respiration yields an overall energy gain of how many ATP molecules? | 36-38 ATP molecules this process is more beneficial to yeast than fermentation -needs oxygen as substrate -inhibited by high sugar concentration. |
| Louis Pasteur concluded what? | That aeration inhibits alcoholic fermentation |
| glyceropyruvic fermentation | generates glycerol as its final product and an alternative pathway to regenrate NAD+ |
| Saccharomyces Cerevisiae in the presence of oxygen will not ferment if | the sugar concentration is higher than 9 grams. -also called the Crabtee affect -high sugar concentration for SC to degenerate |
| Saccharomyces Cerevisiae respiration good conditions are | -low sugar concentration -oxygen is present in the medium |
| Saccaromyces Cerevisiae directs what | the pyruvate to produce ethanol in order to regerate the NAD+ |
| pyruvate is decarboxylated into ethanal by what? | pyruvate decarboxylase -enzyme that needs magnesium and thiamine pyrophosphate as cofactors |
| what reduces ethanal to ethanol? | alcohol dehydrogenase -also recycles NADH to NAD+ |
| Which isoenyzme is chiefly responsible for converting ethanal into ethanol? | isoenzyme 1 |
| What does alcohol dehydrogenase use as a cofactor? | zinc |
| In glyceropyruvic fermentation (glycerol as final product) what combines with ethanol that prevents NAD+ from regenerating via alcohol dehydrogenase? | the presence of sulphite -the yeast need to oxide NADH through an alternative pathway in order to compensate for the NAD+ deficit and this is done by producing glycerol |
| In glyceropyruvic fermentation (glycerol as final product) what is the main product of aldolase reaction that can be oxidized to glycerol-3 phosphate? | dyhroxyacetone phosphate |
| in glyceropyruvic fermentation (glycerol as final product) dyhroxyacetone phosphate can be oxydized to glycerol-3-phosphate by what enzyme? | glycerol-3-phosphate dehydrogenase -reaction is also couples to the oxidation of a molecule of NADH to NAD+ |
| in glyceropyruivc fermentation (glycerol as final product) glycerol-3-phosphate catalyzes the production of glycerol by what? | dephosphorylating glycerol-3-phosphatase. -the production of glycerol consumes ATP but it is necessary to comepensate for the redox imbalance in the cell |
| when. is glycerol mainly produced during fermentation? | the first steps of alcoholic fermentation. yeasts are growing and need a large proportion of pyruvate to increase their biomass. -yeasts produce glycerol as a protector against high osmotic pressures |
| what is the major third component of dry wines? | glycerol is the third major component of dry wines (after water and ethanol -improves wine quality because it confers sweet and mouthfeel sensations. |
Created by:
CherryCoke54