Lecture 24 - Homofermentation: Energy balance glucose 2 ATP...

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Homofermentation: Energy balance glucose fructose-1,6-DP glyceraldehyde-3-P dihydroxyacetone-P pyruvate lactate (lactic acid) H 2 O 2 ATP 2 ADP 2 NAD + 2 NADH 2 NAD + 2 NADH Energy balance: GAIN 2 ATP Proton balance: NADH/NAD (no net gain/loss) 2 moles lactic acid from 1 mole glucose tpi 4 ADP 4 ATP Correction from lecture 23!
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Heterofermentation: Energy balance glucose glyceraldehyde-3-P acetyl-P xylulose-5-P ATP ADP 2 NAD + 2 NADH CO 2 pyruvate lactate (lactic acid) H 2 O 2 ADP 2 ATP NAD + NADH NAD + NADH 2 NAD + 2 NADH ethanol Energy balance: GAIN 1 ATP Proton balance: NADH/NAD (no net gain/loss) 1 mole lactic acid, 1 mole ethanol and 1 mole CO 2 from 1 mole glucose Correction from lecture 23!
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Important Species of LAB in Common foods Lactobacillus helveticus Lactobacillus acidophilus Lactococcus lactis Streptococcus thermophilus Homofermentative Lactobacillus kefir Lactobacillus sanfrancisco (now: sanfrancisensis) Heterofermentative Lactobacillus plantarum Lactobacillus casei Lactobacillus sakei Facultative Heterofermentative
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Pyruvate is an important metabolite in LAB pyruvate Lactic acid Cellular material (nucleic acids, proteins, membrane, etc) Acetyl-CoA acetaldehyde acetate diacetyl acetoin ATP ADP • Pyruvate is formed from sugars, organic acids, and amino acids • Excess pyruvate is toxic to cells • Cells also need ways to re-oxidize NADH formed during sugar metabolism
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Pyruvate can be directed to different end-products pyruvate α -acetolactate acetoin 2,3-butanediol formate acetate acetaldehyde ethanol pyruvate - formate lyase pyruvate dehydrogenase CO 2 acetate acetaldehyde ethanol lactate lactate dehydrogenase Homofermentative LAB
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What affects end-product composition of LAB metabolism? Non-energy generating carbon-metabolism pathways Flavor compounds can also be formed from amino acids Protein Cysteine Methionine CH 3 -SH Methanethiol LAB are auxotrophic for some amino acids. Several LAB species possess Proteolytic systems: Casein proteins in milk Oligopeptides amino acids
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LAB in FOOD PRODUCTION
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Lecture 24 - Homofermentation: Energy balance glucose 2 ATP...

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