1. Lactic acid bacteria spoilage

2. What are LABs? Sugars  lactic acid Fermentative 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

3. 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)

4. 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 (3-methylbutanal)
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

6. Homofermentative lactose utilization
Lactococcus lactis
lactose
ATP
phospho-b-galactosidase
ADP
glucose
galactose-6-P
ATP
ADP
tagatose pathway
glucose-6-P
tagatose-6-P
Embden-Meyerhoff pathway
fructose-6-P
tagatose-1,6-diP
fructose-1,6-diP
4 triose-P

7. 4 triose-P
4 ADP
4 ATP
4 pyruvic acid
4 lactic acid
Lactose  2 ATP + 4 lactic acid

8. Heterofermentative lactose utilization
Some lactobacilli
lactose
b-galactosidase
glucose
galactose
2 glucose-6-P
ATP
ATP
ADP
ADP

9. 2 glucose-6-P
2 CO2
ADP
ATP
2 xyulose-5-P
2 triose-P
2 acetyl phosphate
acetate
2 pyruvic acid
acetaldehyde
2 lactic acid
ethanol

10. 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 (3-methylbutanal)
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

11. Acetaldehyde From L-threonine Threonine aldolase
In yogurt, mainly L. delbrueckii subsp. bulgaricus
threonine
acetaldehyde
glycine
ethanol
chemistry.about.com

12. Second pathway to acetaldehyde
Fig 4.3 from Microbiology and technology of fermented foods (R. Hutkins)

13. Branched chain amino acid catabolism
Lactococcus lactis subsp. lactis biovar maltigenes

14. Diacetyl production From citrate
citrate (C6)
From citrate
Movie popcorn; common in buttermilks (L. lactis subsp. lactis biovar. diacetylactis)
Functions often plasmid-encoded
Acetate (C2)
oxaloacetate (C4)
CO2
pyruvate (C3)
CO2
a-acetolactate (C5)
CO2
diacetyl (C4)
acetoin (C4)
non-enzymatic

15. Ropiness 50-5000 monomers Glucose and galactose most common
Also rhamnose, mannose, fucose, arabinose, xylose, N-acetylglucosamine, N-acetylgalactosamine
Homopolysaccharides
Dextrans, mutans, fructans
Heteropolysaccharides
Extracellular polysaccharides (EPS)
Capsular polysaccharides (CPS)
Ropy polysaccharides

16. Snapshot of EPS diversity (yogurt LAB)
Organism
strain
Exopolysaccharide composition
Sugar ratios in subunits
Lb. delbrueckii subsp. bulgaricus
LY03, rr, Lfi5
Glucose, galactose, rhamnose
Gal:Glu:Rha;
5:1:1
291
Glucose, galactose
Glu:Gal; 3:2
Streptococcus thermophilus
SY89, SY102, SFi39,
Gal:Glu; 1:1
IMD01, CNCMI
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

17. 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