Lactic acid bacteria spoilage What are LABs Lactococcus

Lactic acid bacteria spoilage

What are LABs? • • • • 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 (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

Homofermentative lactose utilization Lactococcus lactis lactose phospho-b-galactosidase ATP ADP Embden. Meyerhoff pathway glucose-6 -P fructose-1, 6 -di. P ATP ADP galactose-6 -P tagatose-1, 6 -di. P 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 CO 2 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 (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

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 (C 6) Acetate (C 2) oxaloacetate (C 4) CO 2 pyruvate (C 3) CO 2 a-acetolactate (C 5) CO 2 diacetyl (C 4) non-enzymatic http: //www. biokemi. org/biozoom /issues/522/articles/2368 acetoin (C 4)

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 LY 03, rr, Lfi 5 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 SY 89, SY 102, SFi 39, Glucose, galactose Gal: Glu; 1: 1 IMD 01, CNCMI Glucose, galactose Gal: Glu; 3: 1 SFi 2 Galactose, rhamnose, Gal: Rha: Glu; 3: 2: 1 glucose MR-IC Galactose, rhamnose, Gal: Rha: Fuc; 5: 2: 1 fucose OR 901 Galactopyranose, rhamnopyranose Gal. P: Rha. P; 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