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Lactic acid bacteria spoilage
What are LABs?
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Lactococcus sp.
Lactobacillus sp.
Leuconostoc sp.
Pediococcus sp.
Oenococcus sp.
Streptococcus sp.
Enterococcus sp.
Sporolactobacillus sp.
Carnobacterium sp.
Aerococcus sp.
Tetragenococcus sp.
Vagococcus sp.
Weisella sp.
• Sugars  lactic acid
• Fermentative
Physiologic features
• Lactic acid main end product
• Limited capacity to synthesize amino acids, vitamins
(esp. Lactobacillus, Lactococcus)
– Lb. johnsonii can’t make any amino acids, for example
• Strictly fermentative metabolism
– No cytochromes, etc.
– Energy generated by substrate-level phosphorylation
• Many prefer lack of oxygen
– Many lack catalase, superoxide dismutase, other enzymes
for dealing with oxygen radicals.
• More acid resistant (in general) than aerobic spoilage
bacteria (especially lactobacilli)
Spoilage or beneficial?
Process
Beneficial (controlled)
Detrimental
(uncontrolled)
Conversion of sugars to
lactic acid
Acid flavor in fermented
meats and dairy products
Sourness of fresh meats,
pasteurized milk
Malty flavor (3methylbutanal)
Malt powder
Pasteurized milk
Ropiness
(exopolysaccharides)
Yogurt
Meats, milk
Acetaldehyde (product of
threonine catabolism)
Yogurt (green apple flavor) Milk
Diacetyl
Buttermilk (butter flavor)
Fresh milk
Homofermentative lactose utilization
Lactococcus lactis
lactose
phospho-b-galactosidase
ATP
ADP
EmbdenMeyerhoff
pathway
glucose
glucose-6-P
fructose-6-P
fructose-1,6-diP
ATP
ADP
galactose-6-P
tagatose-6-P
tagatose-1,6-diP
4 triose-P
tagatose
pathway
4 triose-P
4 ADP
4 ATP
4 pyruvic acid
4 lactic acid
Lactose  2 ATP + 4 lactic acid
Heterofermentative lactose utilization
Some lactobacilli
lactose
b-galactosidase
glucose
ATP
ADP
galactose
2 glucose-6-P
ATP
ADP
2 glucose-6-P
2 CO2
2 xyulose-5-P
2 triose-P
2 acetyl phosphate
2 pyruvic acid
acetaldehyde
2 lactic acid
ethanol
ADP ATP
acetate
Spoilage or beneficial?
Process
Beneficial (controlled)
Detrimental
(uncontrolled)
Conversion of sugars to
lactic acid
Acid flavor in fermented
meats and dairy products
Sourness of fresh meats,
pasteurized milk
Malty flavor (3methylbutanal)
Malt powder
Pasteurized milk
Ropiness
(exopolysaccharides)
Yogurt
Meats, milk
Acetaldehyde (product of
threonine catabolism)
Yogurt (green apple flavor) Milk
Diacetyl
Buttermilk (butter flavor)
Fresh milk
Acetaldehyde
• From L-threonine
• Threonine aldolase
• In yogurt, mainly L. delbrueckii
subsp. bulgaricus
threonine
acetaldehyde
glycine
ethanol
chemistry.about.com
Second pathway to acetaldehyde
Fig 4.3 from Microbiology and technology of fermented foods (R. Hutkins)
Branched chain amino acid catabolism
Lactococcus lactis subsp. lactis biovar maltigenes
http://femsre.oxfordjournals.org/content/29/3/591
Diacetyl production
• From citrate
• Movie popcorn; common in
buttermilks (L. lactis subsp.
lactis biovar. diacetylactis)
• Functions often plasmidencoded
citrate (C6)
Acetate (C2)
oxaloacetate (C4)
CO2
pyruvate (C3)
CO2
a-acetolactate (C5)
CO2
diacetyl (C4)
non-enzymatic
http://www.biokemi.org/biozoom
/issues/522/articles/2368
acetoin (C4)
Ropiness
• 50-5000 monomers
• Glucose and galactose most common
– Also rhamnose, mannose, fucose, arabinose,
xylose, N-acetylglucosamine, Nacetylgalactosamine
• Homopolysaccharides
– Dextrans, mutans, fructans
• Heteropolysaccharides
• Extracellular polysaccharides (EPS)
– Capsular polysaccharides (CPS)
– Ropy polysaccharides
http://www.healthyfacilitiesinstitute.com/p_281-Biofilm
Snapshot of EPS diversity (yogurt LAB)
Organism
strain
Lb. delbrueckii LY03, rr, Lfi5
subsp.
bulgaricus
Streptococcus
thermophilus
Exopolysaccharide
composition
Sugar ratios in subunits
Glucose, galactose,
rhamnose
Gal:Glu:Rha;
5:1:1
291
Glucose, galactose
Glu:Gal; 3:2
SY89, SY102, SFi39,
Glucose, galactose
Gal:Glu; 1:1
IMD01, CNCMI
Glucose, galactose
Gal:Glu; 3:1
SFi 2
Galactose,
rhamnose, glucose
Gal:Rha:Glu; 3:2:1
MR-IC
Galactose,
rhamnose, fucose
Gal:Rha:Fuc; 5:2:1
OR 901
Galactopyranose,
rhamnopyranose
GalP:RhaP; 5:2
Importance of EPS production for
yogurt production
• Increases viscosity
• Reduce syneresis
• Save money:
– Decrease milk solids added prior to heating
– Increase water content
• “Clean” label