Lecture+24+LAB+dairy+fermentations+_color_

Lecture+24+LAB+dairy+fermentations+_color_ - LAB...

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LAB fermentations FST104 March 12, 2012 Factors which influence the end- products of LAB metabolism Carbon-source (sugars) available Presence of air (oxygen) Presence of citrate Presence of other organic compounds (amino acids) pH and temperature
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Carbon-source (sugars) available When pentoses are available to heterofermenters : No CO 2 is produced (less carbonation in the product) glucose glucose-6-P 6-phosphogluconate ribulose-5-P glyceraldehyde-3-P acetyl-P xylulose-5-P CO 2 RIBOSE Carbon-source (sugars) available When fructose is available to heterofermenters : Mannitol is produced (and extra ATP!) mannitol
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Hydroxyl radical Hydrogen peroxide Oxygen Superoxide anion O 2 H 2 O 2 O 2 . - HO . - H 2 O Effects of air (Oxygen) on fermentation Peroxidase RH R+ NADH Oxidase NADH NAD + Homo- and Hetero-fermenters NADH oxidase does NOT result in energy production but rather restores NAD + to the cell. Less lactate, more pyruvate Recycling of NADH+H + Brooijmans, J Bacteriol 2007 Effects of air (Oxygen) on fermentation
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pyruvate Lactic acid Cellular components (nucleic acids, proteins, membrane, etc ) Acetyl-CoA acetaldehyde (ethanol) acetate diacetyl acetoin ATP ADP Excess pyruvate is used to synthesis cell components, increase ATP yield, or restore NADH+H/NAD ratios
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Lecture+24+LAB+dairy+fermentations+_color_ - LAB...

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