Transcript Lactic Acid Bacteria: Characteristics

THREE TYPES OF FOOD
FERMENTATION
• Alcohol
• Acetic Acid
• Lactic Acid - Largest of all
– Homofermentative
– Heterofermentative
Bacteria
lactic acid bacteria
acetic acid bacteria
food bioprocessing
food biopreservation
Probiotic
FOOD
FERMENTATIONS
Lactic Acid Bacteria
– Vegetables and Fruits
SWEET
PICKLES
Lactobacillus helveticus
Lactobacillus delbrueckii
sub. bulgaricus
Lactobacillus lactis
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
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
FOOD FERMENTATIONS
Lactic Acid Bacteria
– Meats
FOOD FERMENTATIONS
Lactic Acid Bacteria
– Dairy Products
FOOD FERMENTATIONS
Lactic acid with other microbes
Dairy Products
• With other bacteria
• With yeasts
• With molds
Vegetable Products
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
Lactic 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)
Lactic 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)
Lactic 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
Lactic Acid Bacteria: Divisions
• Group I: Strict homofermenters
• Group II: Facultative heterofermenters
• Group III: Strict heterofermenters
Homofermentative Metabolism
85% of Glucose
Glucose
Lactic acid
Pyruvate via glycolytic pathway
OO
HO-C-C-CH3
Pyruvate
NADH2
NAD+
O OH
HO-C-CH-CH3
Lactate
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. Acetylphosphate can be converted to acetate and
ATP or reduced to ethanol without ATP
production.
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.
Pentose Phosphate Pathway
Glucose
Phospho-6-gluconate
ATP ADP
NADP+
NADPH
CO2
Ribulose 5-phosphate
NADP+
NADPH
Xylulose 5-phosphate
Acetyl-phosphate
ADP
Acetate
ATP
NADH
NAD+
Acetaldehyde
NADH
Glyceraldehyde 3- phosphate
(glycolysis)
ATP
Pyruate
NAD+
Ethanol
ADP
Lactate
Lactic Acid Bacteria: Genera
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Oenococcus
Pediococcus
Lactobacillus
Leuconostoc
Lactobacillus
Homolactic on hexoses
Heterolactic on hexoses
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L. bavaricus
L. casei
L. homohoichii
L. curvatus
L. saki
L. plantarum
L. fermentum
L. brevis
L. buchneri
L. fructovorans
L. hilgardii
Bacteriocins
• Antimicrobial peptides produced by some
bacteria that inhibit closely related species
• Membrane-active agents that form pores in
cytoplasmic membrane and dissipate protonmotive force
• Significant in food safety to control pathogens
– Lactococcus lactis subsp. lactis and NISIN
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.