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THREE TYPES OF FOOD FERMENTATION
•Alcohol•Acetic Acid•Lactic Acid - Largest of all
– Homofermentative– Heterofermentative
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Bacteria
lactic acid bacteriaacetic acid bacteria
food bioprocessingfood biopreservation
Probiotic
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FOOD FERMENTATIONS
Lactic Acid Bacteria– Vegetables and Fruits
SWEET PICKLES
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Lactobacillus helveticus Lactobacillus delbrueckii sub. bulgaricus
Lactobacillus lactis
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Fermented Milks
• majority of fermented milk products rely on lactic acid bacteria belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus– gram-positives that tolerate acidic
conditions, are non-spore forming, and are aerotolerant with a strictly fermentative metabolism
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Fermented Milks…• mesophilic
– Lactobacillus and Lactococcus– buttermilk and sour cream
• thermophilic – Lactobacillus and Streptococcus– yogurt
• probiotics– Lactobacillus and Bifidobacterium– addition of microbes to the diet to improve
health beyond basic nutritive value
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FOOD FERMENTATIONS
Lactic Acid Bacteria– Meats
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FOOD FERMENTATIONS
Lactic Acid Bacteria– Dairy Products
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FOOD FERMENTATIONS
Lactic acid with other microbesDairy Products
• With other bacteria• With yeasts• With molds
Vegetable Products
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Lactic acid bacteria (LAB)
• G+, non-spore forming cocci or rods• Microaerophilic or anaerobic• Metabolize carbohydrates through
fermentative pathways– Acid production as the major end-product
• Common genera– Lactococcus, Lactobacillus, Leuconostoc,
Pediococcus, Streptococcus, Oenococcus
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Lactic Acid BacteriaLactic Acid Bacteria
• Gram (+) rods (Lactobacillus) and cocci (Streptococcus, Lactococcus, Leuconostoc)
• Produce large amount of lactic acid• Aerotolerant anaerobes: grow
fermentatively• Require many growth factors (vitamins
and amino acids)• Found in nutrient-rich environments
(decomposition)
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Lactic Acid BacteriaLactic Acid Bacteria
• Used to ferment or culture foods for 4000 years• Used in fermenting yogurt, cheese, butter, kefir
and in pickling vegetables• Lactose (milk sugar) converted to lactic acid; low
pH precipitates protein, causing curdling• Low pH also inhibits growth of other bacteria• Give tart taste to fermented milks• Growth is self-limiting (build up of waste products)• Used in probiotics (presence in livestock feed
inhibits E. coli)• Also produce bacteriocins (antimicrobial agents)
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Lactic Acid BacteriaLactic Acid Bacteria
• Produce large amount of lactic acid, lowering pH
• Can grow at < pH 5• Predominate in acidic environment if
it:– Is anaerobic– Is rich in nutrients– Contains a fermentable carbohydrate
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Lactic Acid Bacteria: Divisions
• Group I: Strict homofermenters
• Group II: Facultative heterofermenters
• Group III: Strict heterofermenters
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Homofermentative Metabolism
85% of Glucose Lactic acid
Glucose Pyruvate via glycolytic pathway
HO-C-C-CH3 Pyruvate
HO-C-CH-CH3 Lactate
O O
O OH
NADH2
NAD+
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Heterofermentative Metabolism
Organisms metabolize glucose via the pentose phosphate pathway.
End products can vary depending upon level of aeration and presence of other proton and electron acceptors. Acetyl-phosphate can be converted to acetate and ATP or reduced to ethanol without ATP production.
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Pentose Phosphate Pathway
Lactic Acid Bacteria can also metabolize pentoses such as ribose, arabinose and xylose, via the pentose phosphate pathway.
Acetyl-phosphate leads to the generation of acetate and ATP exclusively in pentose metabolism.
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Pentose Phosphate Pathway
Glucose Phospho-6-gluconate
Ribulose 5-phosphate
Xylulose 5-phosphate
CO2
Glyceraldehyde 3- phosphate
Pyruate
Lactate
Acetyl-phosphate
Acetate Acetaldehyde
Ethanol
(glycolysis)
NADP+
NADPH
NADP+
NADPH
NADH
NAD+
NADH
NAD+ADP
ATP
ADP
ATP
ATP ADP
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Lactic Acid Bacteria: Genera
• Oenococcus
• Pediococcus
• Lactobacillus
• Leuconostoc
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Lactobacillus
Homolactic on hexoses
• L. bavaricus• L. casei• L. homohoichii• L. curvatus• L. saki• L. plantarum
Heterolactic on hexoses
• L. fermentum• L. brevis• L. buchneri• L. fructovorans• L. hilgardii
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Bacteriocins
• Antimicrobial peptides produced by some bacteria that inhibit closely related species
• Membrane-active agents that form pores in cytoplasmic membrane and dissipate proton-motive force
• Significant in food safety to control pathogens– Lactococcus lactis subsp. lactis and NISIN
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Nisin
• Class I bacteriocin: lantibiotic, <5 KDa
• Producer: Lactococcus lactis subsp. lactis
• Active against G+ bacteria (Clostridium botulinum, Listeria monocytogenes, LAB)
• Commercially available
• Cheese and dairy products, canned foods, mayonnaise
• Only bacteriocin approved for use in U.S.