micro of fermented foods

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Microorganisms in Food and Factors Affecting Them Hungate (1962)

Microbiology of Fermented Foods

What kinds of organisms occur? What activities do they perform and how are these activities interrelated? In what number does each kind of organism occur? What is the magnitude of its activity, and what factors influence this magnitude?

Harrison FDST 8090

Homeostasis e.g., pH Intracellular pH maintained within narrow rangeDone by pumping protons out Cell expends energy to maintain homeostasis

Microbial Physiology and Metabolism

Glycolytic PathwaysEmbden-Meyerhof-Parnas Pathway Entner-Doudoroff Pathway Heterofermentative Catabolism Homofermentative Catabolism

Shift of energy from biosynthesis to maintenance of homeostasis inhibits growth If energy needs exceed energy production the cell dies

Tricarboxylic Acid (TCA) Cycle Electron Transport ChainHarrison FDST 8090

Harrison FDST 8090

Microbial Physiology and Metabolism AerobesUse the electron transport system Use molecular O2 as the terminal electron acceptor during oxidative phosphorylationElectrons travel down the chain and protons are pumped out forming a proton gradient drives ATP production Aerobic bacteria Oxidizes glucose to CO2 O2 is reduced to water 38 ATP produced per glucose moleculeHarrison FDST 8090 Harrison FDST 8090

In Aerobes Only

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Microbial Physiology and Metabolism AnaerobesLack electron transport systemReduces internal compound through fermentation 1-2 ATP produced

Microbial Physiology and Metabolism AnaerobesHave fermentative metabolismOxidizes carbohydrates in absence of an external electron acceptor Terminal electron acceptor is an organic product from the degradation of the carbohydratee.g., pyruvic acid is reduced to lactic acid

Use sulfur and nitrogen compounds as terminal electron acceptors in anaerobic respiration or

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 8090

FermentationPurposeMicrobial standpointObtain energy for growth and reproduction

Chemical Alterations during FermentationProduction of desirable end-productsBalance of different end-products and intermediate products Lactic, acetic, propionic acids, CO2, ethanol, flavor cpds

Human standpointProduce desirable flavor &/or aroma traits Product preservation Create a variety of products

What is produced depends on:Which m/o are present Which enzymes are active

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Fermentation Practices

Consider factors affecting growth ofDesired m/o Undesired m/o

Can influence:Rate of reactions Final products produced

Harrison FDST 8090

Harrison FDST 8090

Inoculation Types

Fermentative microorganisms

Natural fermentationsNatural microflora present on raw product

Variety bacteria, yeasts, molds Possible to use purified enzymeIf only 1 enzymatic reaction is involved e.g., Immobilized enzymatic fermentation Can be faster, better control over rate of conversionHarrison FDST 8090

Controlled fermentationKnown culture Starter culturesSingle or mixed strainsHarrison FDST 8090

Fermentation Pathways

Types of Pathways Homofermentative fermentation>90% of end product is lactic acid Embden-Meyerhof-Parnas PathwayAldolase and hexose isomerase present 1 glucose molecule 2 lactic acid molecules AdvantagesFor microbe 2 ATPs produced For humans lactic acid produced

Harrison FDST 8090

(Jay, 2000)

Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Types of Pathways Heterofermentative fermentationHexose Monophosphate Pathway (or Pentose Pathway)Phosphoketolase present 1 glucose 1 lactic acid + 1 CO2 + 1 ethanol AdvantagesFor microbe 1 ATP produced For humans lactic acid, CO2, ethanol produced; more flavor and aroma compounds than homofermentation

Harrison FDST 8090

Harrison FDST 8090

Types of Pathways Alcoholic fermentation by yeasts1 glucose 2 CO2 + 2 ethanol AdvantagesFor microbe 2 ATPs 1 & 2 C-cpds produced

For humans CO2, ethanol produced

Harrison FDST 8090

Harrison FDST 8090

Genetic ModificationsModify microbee.g., Dairy starters Most plasmid related traits Primarily: Lactococcus, Streptococcus, Lactobacillus Desirable traits:Phage resistance Lactose fermenting ability Proteolytic activity Citrate use Nisin productionHarrison FDST 8090 Harrison FDST 8090

Genetic ModificationsProduction of food grade yeastSingle cell proteins

Immobilized enzymes Production of enzymese.g., Microbial production of rennin

Production of proteins

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Fermented FoodsFermented Dairy ProductsExamples covered next


Fermented Meat ProductsCovered in the Microbiology of Meat, Poultry, Fish and Shellfish section

Fermented Vegetables and FruitsWide variety of final products Covered some in lab e.g., sauerkraut Other vegetable types e.g., pickles following section Beer and wine following section Other products covered in handoutHarrison FDST 8090 Harrison FDST 8090

True buttermilk - What remains after cream is churned into butter Cultured buttermilk - commercial product

Cultured ButtermilkMilk - skim, reconstituted NFDM HeatDestroys unwanted m/o Improves body

Cultured ButtermilkIncubationto TA of 0.8-0.9% lactic acid

Starter culture addedForm curd Lactococcus lactis subsp. lactis Lactococcus lactis subsp. cremoris Flavor: diacetyl, acetoin via citric acid fermentation Leuconostoc mesenteroides subsp. cremoris Lactococcus lactis subsp.lactis biovar diacetilactis Leuconostoc mesenteroides subsp. dextranicumHarrison FDST 8090 Harrison FDST 8090

Break-up curd Cool Package Distribute

Acidophilus MilkDesire - to ingest viable bacteria Lactobacillus acidophilus - easily overgrown so milk is heat treated to kill other m/o Incubateto 0.6-0.7% lactic acid Acid produced with no aroma

Acidophilus Milk

Sweet acidophilus milkConcentrate of L. acidophilus added to cold milk sweet - no acid produced

Cool, etc.

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Acidophilus MilkHealth benefitsL. acidophilus implants in intestines Possible benefitsPathogen inhibitor Carcinogen suppression Enzyme source

YogurtMilk - 12-15% milk solids-not fat Heat then cool InoculateLactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus - 1:1 ratio

Incubate - 45oC for 3-5 hto TA of 0.85-0.9% lactic acid Final level attained after packaging

Cool, etc.Harrison FDST 8090 Harrison FDST 8090

Kefir1% ethanol, 1% lactic acid Microorganisms - variesLactobacillus brevis, Lactobacillus delbrueckii subsp. bulgaricus,Torulopsis, etc. Kefir grainsMass of fermenting microbes Used to seed next batch

Harrison FDST 8090

Harrison FDST 8090

Basic CheesemakingMilk

Lactic acid bacteria added

Acid produced

Milk coagulated

W hey expelled


Harrison FDST 8090


Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Cheese - ProcessingMilkInitial microbiota Pasteurized or unpasteurizedHeat may result in soft, fragile curds Heat destroys natural enzymes in milk Heat eliminates pathogens

Harrison FDST 8090

Harrison FDST 8090

Cheese - ProcessingCurd formationTemperatureHold after starters are added Acid produced

Cheese - ProcessingStarter culturesLactic acid - from 1 or more strainsPromotes curd formation Destroys, retards or prevents growth of spoilage and pathogenic m/o Influences enzymatic changes - greater activity at reduced pH

Rennet added to ppt. casein

Harrison FDST 8090

Harrison FDST 8090

Cheese - ProcessingStarter cultures Lactic acid producers requiring moderate curd cookUp to 40oC Single or mixed strainsLactococcus lactis subsp. lactis Lactococcus lactis subsp. cremoris Lactococcus lactis subsp. lactis biovar diacetilactis

Cheese - ProcessingStarter culturesOthersPropionbacterium shermanii Penicillium roqueforti Pencillium camemberti

Addition of startersMay be added to vat, rubbed on surfaces of wheels, sprayed, etc.

Thermophilic lactic acid producersCurd cook 45-54oC Single or mixed strainsStreptococcus thermophilus Lactobacillus delbrueckii subsp. bulgaricusHarrison FDST 8090 Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods


Cheese - ProcessingShrinking of curdCut-up curd Heat, stir, and measure %TA of whey Expel whey SaltEnhances flavor Helps control spoilage m/o growth

Forms and pressure

Harrison FDST 8090

Harrison FDST 8090

Cheese - ProcessingRipening (Curing)Flavor and body characteristics develop Enzymatic changes of fat, protein, etc. enhance flavor Time varies according to variety and temperature

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 8090

Harrison FDST 4030/6030 Microbiology of Fermented Foods



MilkLactococcus lactis or L. cremoris (39% water) Surface GrowthHarrison FDST 8090

Cheese - SpoilagePutrid, unclean, yeasty, fermented, rancid flavors develop Yeasts, molds, anaerobic sporeformersMold on surfacesPrevent by waxing and vacuum packaging

Cheese - Safety IssuesVariety of patho


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