Micro of Fermented Foods
-
Upload
ganeshmohan93 -
Category
Documents
-
view
78 -
download
2
description
Transcript of Micro of Fermented Foods
HarrisonFDST 4030/6030Microbiology of Fermented Foods 1
HarrisonFDST 8090
Microbiology Microbiology ofof
Fermented Fermented FoodsFoods
Microorganisms in Food and Factors Affecting Them
Hungate (1962)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?
HarrisonFDST 8090
Homeostasis – e.g., pH
Intracellular pH maintained within narrow range
Done by pumping protons outCell expends energy to maintain homeostasis
Shift of energy from biosynthesis to maintenance of homeostasis inhibits growthIf energy needs exceed energy production the cell dies
HarrisonFDST 8090
Microbial Physiology and Metabolism
Glycolytic PathwaysEmbden-Meyerhof-Parnas PathwayEntner-Doudoroff PathwayHeterofermentative CatabolismHomofermentative Catabolism
Tricarboxylic Acid (TCA) CycleElectron Transport Chain
HarrisonFDST 8090
Microbial Physiology and Metabolism -Aerobes
Use the electron transport system Use molecular O2 as the terminal electron acceptor during oxidative phosphorylation
Electrons travel down the chain and protons are pumped out forming a proton gradient –drives ATP productionAerobic bacteria
Oxidizes glucose to CO2
O2 is reduced to water38 ATP produced per glucose molecule
HarrisonFDST 8090
In Aerobes Only
HarrisonFDST 4030/6030Microbiology of Fermented Foods 2
HarrisonFDST 8090
Microbial Physiology and Metabolism -Anaerobes
Lack electron transport systemReduces internal compound through fermentation 1-2 ATP produced
Use sulfur and nitrogen compounds as terminal electron acceptors in “anaerobic respiration” or
HarrisonFDST 8090
Microbial Physiology and Metabolism -Anaerobes
Have fermentative metabolismOxidizes carbohydrates in absence of an external electron acceptor Terminal electron acceptor is an organic product from the degradation of the carbohydrate
e.g., pyruvic acid is reduced to lactic acid
HarrisonFDST 8090
HarrisonFDST 8090
HarrisonFDST 8090
Fermentation
Purpose Microbial standpoint
Obtain energy for growth and reproductionHuman standpoint
Produce desirable flavor &/or aroma traitsProduct preservationCreate a variety of products
HarrisonFDST 8090
Chemical Alterations during Fermentation
Production of desirable end-productsBalance of different end-products and intermediate productsLactic, acetic, propionic acids, CO2, ethanol, flavor cpds
What is produced – depends on:Which m/o are present Which enzymes are active
HarrisonFDST 4030/6030Microbiology of Fermented Foods 3
HarrisonFDST 8090
HarrisonFDST 8090
Fermentation Practices
Consider factors affecting growth ofDesired m/oUndesired m/o
Can influence: Rate of reactions Final products produced
HarrisonFDST 8090
Inoculation Types
Natural fermentationsNatural microflora present on raw product
Controlled fermentationKnown culture“Starter cultures”
Single or mixed strains
HarrisonFDST 8090
Fermentative microorganisms
Variety – bacteria, yeasts, moldsPossible to use purified enzyme
If only 1 enzymatic reaction is involvede.g., Immobilized enzymatic fermentationCan be faster, better control over rate of conversion
HarrisonFDST 8090
Fermentation Pathways
(Jay, 2000) HarrisonFDST 8090
Types of Pathways
Homofermentative fermentation>90% of end product is lactic acidEmbden-Meyerhof-Parnas Pathway
Aldolase and hexose isomerase present1 glucose molecule 2 lactic acid moleculesAdvantages
For microbe – 2 ATPs producedFor humans – lactic acid produced
HarrisonFDST 4030/6030Microbiology of Fermented Foods 4
HarrisonFDST 8090
HarrisonFDST 8090
Types of Pathways
Heterofermentative fermentationHexose Monophosphate Pathway (or Pentose Pathway)
Phosphoketolase present 1 glucose 1 lactic acid + 1 CO2 + 1 ethanol Advantages
For microbe – 1 ATP producedFor humans – lactic acid, CO2, ethanol produced; more flavor and aroma compounds than homofermentation
HarrisonFDST 8090
Types of Pathways
Alcoholic fermentation by yeasts1 glucose 2 CO2 + 2 ethanol Advantages
For microbe –2 ATPs1 & 2 C-cpds produced
For humans – CO2, ethanol produced
HarrisonFDST 8090
HarrisonFDST 8090
Genetic Modifications
Modify microbee.g., Dairy starters
Most plasmid related traitsPrimarily: Lactococcus, Streptococcus, LactobacillusDesirable traits:
Phage resistanceLactose fermenting abilityProteolytic activityCitrate useNisin production
HarrisonFDST 8090
Genetic Modifications
Production of food grade yeast Single cell proteins
Immobilized enzymesProduction of enzymes
e.g., Microbial production of rennin Production of proteins
HarrisonFDST 4030/6030Microbiology of Fermented Foods 5
HarrisonFDST 8090
Fermented Foods
Fermented 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., sauerkrautOther vegetable types – e.g., pickles – following sectionBeer and wine – following sectionOther products covered in handout
HarrisonFDST 8090
Buttermilk
True buttermilk - What remains after cream is churned into butterCultured buttermilk - commercial product
HarrisonFDST 8090
Cultured Buttermilk
Milk - skim, reconstituted NFDMHeat
Destroys unwanted m/o Improves body
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 diacetilactisLeuconostoc mesenteroides subsp. dextranicum
HarrisonFDST 8090
Cultured Buttermilk
Incubation to TA of 0.8-0.9% lactic acid
Break-up curdCoolPackage Distribute
HarrisonFDST 8090
Acidophilus Milk
Desire - to ingest viable bacteria Lactobacillus acidophilus - easily overgrown so milk is heat treated to kill other m/oIncubate
to 0.6-0.7% lactic acidAcid produced with no aroma
Cool, etc.
HarrisonFDST 8090
Acidophilus Milk
Sweet acidophilus milk Concentrate of L. acidophilus added to cold milk“sweet” - no acid produced
HarrisonFDST 4030/6030Microbiology of Fermented Foods 6
HarrisonFDST 8090
Acidophilus Milk
Health benefitsL. acidophilus implants in intestinesPossible benefits
Pathogen inhibitorCarcinogen suppressionEnzyme source
HarrisonFDST 8090
Yogurt
Milk - 12-15% milk solids-not fatHeat then cool Inoculate
Lactobacillus 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.
HarrisonFDST 8090
Kefir
1% ethanol, 1% lactic acidMicroorganisms - varies
Lactobacillus brevis, Lactobacillus delbrueckiisubsp. bulgaricus,Torulopsis, etc. Kefir grains
Mass of fermenting microbes Used to seed next batch
HarrisonFDST 8090
HarrisonFDST 8090
Basic Cheesemaking
Ripened
Salted
Whey expelled
Milk coagulated
Acid produced
Lactic acid bacteria added
Milk
HarrisonFDST 8090
HarrisonFDST 4030/6030Microbiology of Fermented Foods 7
HarrisonFDST 8090
HarrisonFDST 8090
Cheese - Processing
MilkInitial microbiota Pasteurized or unpasteurized
Heat may result in soft, fragile curdsHeat destroys natural enzymes in milk Heat eliminates pathogens
HarrisonFDST 8090
Cheese - Processing
Curd formation Temperature
Hold after starters are added Acid produced
Rennet added to ppt. casein
HarrisonFDST 8090
Cheese - Processing
Starter culturesLactic acid - from 1 or more strains
Promotes curd formationDestroys, retards or prevents growth of spoilage and pathogenic m/oInfluences enzymatic changes - greater activity at reduced pH
HarrisonFDST 8090
Cheese - Processing
Starter culturesLactic acid producers requiring moderate curd cook
Up to 40oCSingle or mixed strains
Lactococcus lactis subsp. lactisLactococcus lactis subsp. cremorisLactococcus lactis subsp. lactis biovar diacetilactis
Thermophilic lactic acid producersCurd cook 45-54oCSingle or mixed strains
Streptococcus thermophilusLactobacillus delbrueckii subsp. bulgaricus
HarrisonFDST 8090
Cheese - Processing
Starter culturesOthers
Propionbacterium shermaniiPenicillium roquefortiPencillium camemberti
Addition of starters May be added to vat, rubbed on surfaces of wheels, sprayed, etc.
HarrisonFDST 4030/6030Microbiology of Fermented Foods 8
HarrisonFDST 8090
HarrisonFDST 8090
Cheese - Processing
Shrinking of curdCut-up curdHeat, stir, and measure %TA of wheyExpel wheySalt
Enhances flavor Helps control spoilage m/o growth
Forms and pressure
HarrisonFDST 8090
HarrisonFDST 8090
Cheese - Processing
Ripening (Curing)Flavor and body characteristics developEnzymatic changes of fat, protein, etc. enhance flavorTime varies according to variety and temperature
HarrisonFDST 8090
HarrisonFDST 8090
HarrisonFDST 4030/6030Microbiology of Fermented Foods 9
HarrisonFDST 8090
Milk
Whey (93% water, 5% lactose)
Firm Curd (Coagulated casein)
Unripened Cheese
Soft Cheese (>39% water) Surface Growth
Hard CheeseInterior Bacterial Growth
Semihard Cheese
Cream Cheese
Lactococcus lactis or L. cremoris (<38oC)Streptococcus thermophilus &
Lactobacillus sp. (50oC)Rennin
Salt added
Cottage Cheese
Cream
Ripening – temperatures, incubation times, organisms vary depending on the cheese
Bacteria or fungi growsDegradation and conversion of the curd
Cheesemaking
HarrisonFDST 8090
Cheese - Processing
ProblemsInadequate acid formation
Bad starterResidual antibioticResidual sanitizerBacteriophages
Rotate starters to minimize
HarrisonFDST 8090
Cheese - Spoilage
Putrid, unclean, yeasty, fermented, rancid flavors developYeasts, molds, anaerobic sporeformers
Mold on surfacesPrevent by waxing and vacuum packaging
“gassy” - Clostridium spp.
HarrisonFDST 8090
Cheese - Safety Issues
Variety of pathogens possiblebrucellosis, botulism, shigellosis, salmonellosis, staphylococcal food poisoning, listeriosis, etc.Most common problems
Soft cheese Improperly processed
Amine formation – histamine
HarrisonFDST 8090
Fermented Vegetables
Preservation principlesReduce activities of native enzymes
PectinolyticOxidativve
Inhibit undesirable m/oFactors that can be manipulated
Anaerobic conditionsNaClAcidTemperature – 18-27oC
HarrisonFDST 8090
Microorganisms Involved
Normal microbiotaPrimary ones:
Leuconstoc mesenteroidesLactobacillus plantarumPediococcus cerevisiaeLactobacillus brevis
What role does each serve?
HarrisonFDST 4030/6030Microbiology of Fermented Foods 10
HarrisonFDST 8090
General Flow Sheet for Fermented Vegetables
Raw material Remove damaged and spoiled material Clean/Wash
Cored/PeeledBlanched/CookedPierced/Shred
Place in FermenterAdd Water Addition of Sugars, Starter Cultures, NaCl
Fermentation
Unpacked
ContainersFilled
Fresh FermentedProducts
Blached
Canned Pasteurized
Pasteurized Fermented Products HarrisonFDST 8090
Pickle Fermentation - Salt Stock Procedure
Raw cucumbers placed in wooden brine tanks5% NaCl added
Inhibits undesirable microbes and Extracts water and water soluble substances -e.g., sugars which are then fermented to lactic acid
Over 6-9 weeks NaCl increased to 15.9%
HarrisonFDST 8090
Pickle Fermentation - Salt Stock Procedure
Microorganisms involved in the fermentationLeuconstoc mesenteroidesLactobacillus plantarum - Most importantPediococcus cerevisiae - Important Lactobacillus brevis - Undesirable; Gas production Enterococcus faecalis
HarrisonFDST 8090
Pickle Fermentation - Salt Stock Procedure
Spoilage Economic lossBloaters - Gas trapped in cucumbers Caused by Enterobacter spp., lactobacilli, pediococciSoftening – Caused by pectolytic organisms, e.g., Bacillus, Fusarium, Penicillium, Phoma, Cladosporium, Alternaria, Mucor, Asperigillus,others Off-colors, etc
HarrisonFDST 8090
Pickle Fermentation - Controlled Fermentation
ProcedureCucumbers placed into chlorinated brine with 6-7% NaCl Brine acidified with acetic acidSodium acetate addedInoculated with P. cerevisiae and L. plantarum or just L. plantarum10-12 day fermentationFinal pickle pH ~4.0
AdvantagesReduces economic lossMore uniform pickleFaster than salt stock
Spoilage possible – Bloaters, Softening, Off-colors
HarrisonFDST 4030/6030
Changes During Pickle Fermentation
(Jay, 2000)
HarrisonFDST 4030/6030Microbiology of Fermented Foods 11
HarrisonFDST 8090
Sauerkraut Fermentation
Starter culture - natural microbiota Procedure
Raw cabbage2.25-2.5% NaCl
HarrisonFDST 8090
Changes during Sauerkraut Fermentation
0123456789
10
0 5 10 15
Days
pH o
r L
og c
fu/m
l
0
5
10
15
20
25
Red
Ox
Pote
ntia
l
pH APC LAB Yeasts RedOx
HarrisonFDST 8090
Flow Chart for Brewing
Malting
Milling, Mashing
Wort Boiling
Fermentation
Post-fermentation Treatments
Conversion of barley starch to fermentable sugars and protein to free amino acids
Hot water extraction of sugars, amino acids, and other yeast nutrients and enzymes – Yields sweet wort
Boiling with hops to extract aroma and bitter compounds; Heated to sterilize – Yields hopped wort
S. cerevisiae fermentation of sugars to ethanol & CO2
Maturation, clarification, packaging, pasteurizationHarrisonFDST 4030/6030
Typical Brewing Changes
(Doyle et al, 2002)
HarrisonFDST 8090
Flow Chart for Red Wine Making
Grapes Harvested Grapes Crushed (SO2 added optional) Add Starters (optional)
Maceration and Partial Fermentation
(color and tannin extraction)
Pressing(removal of skins)
Fermentation Completion;Racking Off Yeast Lees
WineMalolactic
Fermentation(optional)
Aged (in oak barrels, etc.)
Fined, Clarified, Packaged
Final Product –Red Wine
HarrisonFDST 8090
Flow Chart for WhiteWhiteWhite Wine Making
Grapes Harvested Grapes Crushed (SO2 added optional)
Pre-fermentaton; Settling
Pressing(removal of skins)
Add Starters(optional)
Fermentation;Racking Off Yeast Lees
Aged (optional)
Fined, Clarified, Packaged
Final Product –White Wine
White Wine Malolactic Fermentation (optional)
HarrisonFDST 4030/6030Microbiology of Fermented Foods 12
HarrisonFDST 8090
Grapes are emptied into binsand then enter the destemmermachine.
HarrisonFDST 8090
Grapes go to the destemmer-sorting machine
HarrisonFDST 8090
Rotating grape press
HarrisonFDST 8090
Temperature controlled
fermentation vats
HarrisonFDST 8090
HarrisonFDST 8090
HarrisonFDST 4030/6030Microbiology of Fermented Foods 13
HarrisonFDST 8090
HarrisonFDST 8090
Spoilage Microorganisms of Beer and Wine
Beer Spoilage - YeastsSaccharomycesTorulasporaZygosaccharomycesHanseniasporaDekkeraDebaryomycesPichia
Wine Spoilage – BacteriaMicrococcusBacillusPediococcusStreptococcusLactobacillusAcetobacterGluconobacterZymomonasMegaspheraPectinatusObesumbacterium