Lecture 23 - Lactic acid bacteria and lactic fermentations...

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Lactic acid bacteria and lactic fermentations Professor Maria Marco FST104 March 5, 8, and 10, 2010
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What is the definition of fermentation ? Energy metabolism without an electron transport chain Process of making alcoholic beverages Large scale growth of microbes for specific products Process of making a food in which the characteristic properties of the food are the result of extensive microbial growth
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Many types of foods we eat are fermented
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Basic food fermentation patterns Sugars lactic acid, acetic acid, acetaldehyde, diacetyl, CO 2, ethanol ethanol, CO 2 lactic acid bacteria yeast Starch short-chained esters polysaccharides mono/di-saccharides molds Bacillus yeast Proteins amino acids peptides amino acids, amines NH 3 NH 3 molds, Bacillus ( Clostridium ) many microbes Fats (glycerol) fatty acids ketones (esters) molds molds
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LACTIC ACID BACTERIA (part 1) Gram-positive “ubiquitous” : plants, digestive tracts, milk Fermentative metabolism: saccharolytic Degrade mono- and di-saccharides-- not large polysaccharides Produce lactic acid as end-product of metabolism (as low as pH 3.5; pKa of lactic acid)
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LACTIC ACID BACTERIA (part 2) Microaerophiles: grow throughout foods Fastidious (limited biosynthetic capacity) Limited Proteolysis (some species) Stress tolerant: salt: >5% NaCl acid: some grow as low as pH 3 oxygen: anaerobic; microaerophilic temperature: mesophilic and thermophilic alcohol: grow/survive at 12-13%
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Major genera of LAB: phylogeny Division: Firmicutes Class: Bacilli Order: Lactobacillales Genome sizes: approximately 2 million base pairs (Mbp), 2000 genes Lactobacillus Streptococcus Lactococcus Leuconostoc Pediococcus Oenococcus Oenococcus oeni Leuconostoc mesenteroides Pediococcus pentosus Lactobacillus brevis Lactobacillus plantarum Lactobacillus delbrueckii Lactobacillus johnsonii Lactobacillus gasseri Lactobacillus casei Streptococcus thermophilus Lactococcus lactis ssp. cremoris Lactococcus lactis spp. lactis
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Lecture 23 - Lactic acid bacteria and lactic fermentations...

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