Food Micro Exam 1

Front 1

Bacteria vs Fungal cell structure

Back 1

Bacteria- single-cell M/O, lack membrane-bound nucleus, lack other membrane bound organelles (no compartmentalization)

Fungi- Single, multi-cellular, or filamentous organisms, contain membrane-bound nucleus and organelles, Heterotrophic nutrition (saprophytes and parasites)- COMPARTMENTALIZATION

Front 2

Two Phylums of bacteria?

Back 2

Proteobacteria- gram-negatives

Firmicutes- gram-positives

Front 3

G+ vs G- cell envelope structure

Back 3

G+: cytoplasmic membrane, very thick peptidoglycan. Tend to be more heat resistant

G-: cytoplasmic membrane, very thin peptidoglycan envelope but complex with teichoic acid. Tend to be more acid resistant

Front 4

Nitrogeneous Bases of DNA and RNA

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Front 5

Enterobacteriaceae characteristics (general)

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- Gram- negative, rod-shaped

-Motile by peritrichous flagella

-Meosphiles (optimum between 23-35C)

-Facultative anaerobes

-Both respiratory and fermentative metabolism of carbs.

-Reduce nitrate to nitrite (most species)

-Catalase-positive (helps overcome H2O2)

-Oxidase negative-alternative ETC

-Ecology and host range: soil, water, and vegetation, human, animal and plant pathogens, common inhabitants in the GI tract

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TCA Cycle Steps/End-products (diagram)

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Front 7

Fermentation By-products? Diagram

Back 7

By-products: Lactic acid, acetic acid and mixed acid (Esp. Enterobacteriaceae)

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Enterobacteriaceae genera significant to food?

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- Citrobacter

-Enterobacter

-Erwinia

-Escherichia

-Hafnia

-Klebsiella

-Proteus

-Salmonella

-Shigella

-Yersinia

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Coliforms

Back 9

-Indicators of fecal contamination water and food (according to the gov't)

-Fecal vs non-fecal origins

-Coliform genera: Citrobacter, Enterobacter, Escherichia, Klebsiella

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Characteristics of Pseudomonas spp. Morphology

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-Morphology: Gram-negative, rod shaped, motile by polar flagella (in liquid)

-may secrete pigments: Pyoverdin (fluorescein) produced by P. fluorescens and P. aeruginosa. Pyocyanin by P. aeruginosa (detect on agar, food spoilage determinant)

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Pseudomonas spp. Biochemical and physiological characteristics

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-Catalase positive- AEROBIC RESPIRATION

-Oxidase variable, usually positive

-Obligate aerobe

-Some strains can use nitrate as a final electron acceptor during respiration.

-Mesophilic to psychrotrophic.

-Utilize a wide range of organic substances

-No growth factors required

-Compete very efficiently for iron

-Absence of fermentation, photosynthesis, and nitrogen fixation.

-Not acidophiles

-Catabolically diverse

-Bioremediation

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Steps in biofilm formation

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1. Reversible attachment

2. Irreversible attachment-extracellular polysachharides

3. Maturation

4. Dispersion

Front 13

Significance of biofilms for food?

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1. Equipment contamination- when mechanical removal is difficult (pipes, drains etc..)

2. Continuous source of spoilage- one contaminated valve will continue to contaminate all products coming into contact

3. Difficult to remove by washing and sanitization- once film is formed cannot guarantee removal.

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Most common species of Pseudomonas that spoil food?

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P. fluorescens group (most common)

P. fragi

P. lundensis

P. putida

Meat and poultry spoilage! (odor, color, slime)

Dairy- produces heat stable lipases and proteases, spoil milk by causing bitterness, casein breakdown, and robiness due to production of slime and coagulation of proteins.

Butter- Putrid smells (P. putrefaciens), rancid (FFA) from P. fragi or P. fluorescens, Skunk-like smell- P. mephitica, BLACK- P. nigrifaciens

Vegetables- slime from pectin breakdown

Fish and ground meat- sulfidy off smell (H2S) from cysteine breakdown

Front 15

Genera of lactic acid bacteria of importance in food?

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-Lactococcus

-Leuconostoc

-Streptococcus

-Pediococcus

-Lactobacillus

Front 16

Characteristics (general) of LAB?

Back 16

-Gram+

-Nonspore-forming

-Anaerobic (or microaerophilic- don't need it but can tolerate it)

-Catalase negative

-Nutritionally fastidious (needs nutrients from the environment)

-Cannot generate energy by respiration (incomplete TCA cycle and ETS)

-Generate ATP by fermentation with lactic acid as major end product

Front 17

Homolactic vs Heterolactic fermentation?

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Homolactic fermentation: EMP (Embden-Meyerhof-Parnas) pathway glycolysis + lactate dehydrogenase. End products: Lactic acid and ATP. Examples: Lactococcus, S. thermophilus, Pediococcus, some Lactobacillus

Heterolactic fermentation: Phosphoketalase pathway. Under anaerobic conditions: get CO2, lactic acid, ethanol, ATP. Under aerobic conditions: CO2, lactic acid, acetic acid and ATP. *Heterolactic fermentation not that efficient- will use up CHOs in environment quickly. Examples: Leuconostoc, Oenococcus, some Lactobacillus

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Lactobacillus characteristics

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Morphology: Rods or chains

CO2 from glucose: + or -

Cardinal temp: Can be psychrotrophic all the way to thermophilic

Species relevant to fermentation: L. bulgaricus

Species relevant to spoilage: L. fermentum

Species relevant to health: L. acidophilus, L. reuteri (probiotics)

Comments: Diverse genus

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Lactococcus characteristics

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Morphology: Cocci

CO2 from glucose: No

Cardinal temp: Likes milder temperatures (10C-37C) mostly psychrotrophic

Species relevant to fermentation: L. lactis

Species relevant to spoilage: none

Species relevant to health: none

Comments: Lancefield Group N

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Streptococcus characteristics

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Morphology: Cocci, chains (always)

CO2 from glucose: no

Cardinal temp: Thermophilic

Species relevant to fermentation: S. thermophilus

Species relevant to spoilage: none

Species relevant to health: S. pyogenes, S. pneumoniae, S. mutans **VERY BAD!

Comments: Lancefield Group A, B and others

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Pediococcus characteristics

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Morphology: Cocci and tetrads (always)

CO2 from glucose: No

Cardinal temp: Can be psychrotrophic or thermophilic

Species relevant to fermentation: P. acidilactici

Species relevant to spoilage: none

Species relevant to health: none

Comments: High salt tolerance- good in fermentated meats (pepperoni)

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Leuconostoc characteristics

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Morphology: Cocci

CO2 from glucose: YES

Cardinal temp: Milder temperatures 10-37C (psychrotrophic/mesophilic)

Species relevant to fermentation: L. mesenteroides

Species relevant to spoilage: L. carnosum (grows on carcasses)

Species relevant to health: None

Comments: Vegetable fermentation (sauerkraut)

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Types of fermented foods and the LAB used

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Dairy (yogurt, cheese, sour cream)- ex: S. thermophilus

Meat (fermented sausages)- ex: P. acidilactici

Vegetables (pickles, kimchi etc) ex: Leuconostoc, Pediococcus, LAB

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Examples of LAB used as probiotics

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Lactobacillus reuteri, Lactobacillus acidophilus

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Antimicrobials made by LAB?

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-Bacteriocins made by LAB: nisin!

-Also H2O2, acids (acetic, lactic) etc.. can be used as AMA in foods

Front 26

Hemolytic Serology Categories

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Alpha-hemolytic: green partial hydrolysis (Ex: Streptococcus pneumoniae, Streptococcus viridians)

Beta-hemolytic: clear, complete hydrolysis (ex: Streptococcus pyogenes- Type A bacitracin sensitive; Streptococcus agalactiae- Type B bacitracin resistant)

Gamma-hemolytic: No hemolysis- used in foods, non-pathogenic. Ex: Entococcus faecalis, E. faecium

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Basic characteristics of bacterial spores

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-Dormancy and Longevity

-Resistance to deleterious factors: resist factors that bacterial cells can not survive. Eg: heat (hot environment, boiling water), lack of water (arid environment), presence or absence of air (even aerobic spores don't need it), antimicrobial agents

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Whats the name for spore formation?

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Sporulation! It is a stage in the life-cycle of a spore-forming bacterium

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Spore Structure (diagram)

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Front 30

Stages of sporulation in bacteria

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Front 31

Spore transformation to Vegetative Cell (Germination)

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Activation: a treatment to facilitate the germination process, reversible- can be activated by sublethal heat, low pH, chemicals etc. *Must remove outer coats

Germination: degradation events triggered by germinants (nutrients L-alanine, ribosides; non-nutrients: Ca-dipicolinic acid; enzymes: lysozymes; physical process; high hydrostatic pressure), irreversible, loss of heat resistance, release of dipicolinic acid, cortex hydrolysis, core hydration (loss of refractility- phase-bright to phase-dark); decrease in optical density

Outgrowth- development of vegetative cell from a germinated spore- emergence from the spore coat, elongation of the emergent cell

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Factors in spore resistance

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1. Vegetative cell makeup and characteristics- optimum growth temperature of cell will yield same resistance in spore- thermophilic spores>spores of mesophiles>spores of psychtrophiles. More heat exposure increases resistance.

2. Spore structure

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Spore structure- Core SASP resistance

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Resistant to Dry heat, UV radiation, Desiccation and freezing

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Spore structure- Core dehydration resistance

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Resistant to Wet heat and hydrogen peroxide

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Spore structure- Core minerals resistance

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Resistant to dry heat, wet heat and hydrogen peroxide

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Spore structure- Spore Cortex resistance

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Resistant to wet heat, lytic enzymes, hydrogen peroxide. NOT resistant to UV radiation.

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Spore structure- Spore coats resistance

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Resistant to Lytic enzymes, and hydrogen peroxide. Not resistant to wet heat or UV radiation.

Front 38

Heat resistance in spores is a measure of what compared to the vegetative cell?

Back 38

Refers to the temperature at which the decimal reduction (killing by 90%) time of a heated suspension is 10 minutes.

Front 39

Control of spores- Ways to inactivate (sporicidal)

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1. Severe heat (retort)

2. Gamma radiation- heavy; spices use gamma radiation

3. Hydrogen peroxide (high concentration and heat): vapor (used with sterile packaging)

4. Ethylene oxide- in non-foods (disposable pipettes)

5. Chlorine

6. Ozone

7. Combination "hurdle process"

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Control of spores- Inhibition of germination and/or outgrowth (sporostatic)

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1. Bacteriocin: Nisin

2. Nitrite

Front 41

Bacillus cereus

Back 41

Mesophilic aerobe, facultative anaerobe. Importance in foods: food intoxication, cooked rice, pasta, meats, soups, salads, puddings.

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Bacillus subtilis

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Mesophilic aerobe, obligate aerobe. Spoilage: "ropy" bakery product; softening of pickles

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Alicyclobacillus spp.

Back 43

Thermophilic aerobe. Acidophile: growth at pH 2.5-5.5 (opt: 3.5-4). Optimum temp: 46-50C. In foods: flat sour spoilage, spoilage of fruit juices and iced teas

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Bacillus coagulans

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Thermophilic aerobe. Facultative anaerobe. Growth opt >50C. Aciduric: opt pH 6. In foods: flat sour spoilage, spoilage of canned tomato juice and other acid foods.

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Bacillus stearothermophilus

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Thermophilic aerobe. Facultative anaerobe. Growth at 40-70C (opt >60C). In foods: flat sour spoilage; spoilage of low acid canned vegetables.

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Clostridium sporogenes

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Mesophilic anaerobe. Putrefactive anaerobe. In foods: spoilage of canned vegetables (swelling and putrid odor).

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Proteolytic Clostridium botulinum

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Mesophilic anaerobe. Produce toxin types: A, B, F. Digests gelatin, milk and meat. In foods: Food intoxication, home-canned foods; foods subjected to faulty processing or temperature abuse.

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Non-proteolytic Clostridium botulinum

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Mesophilic anaerobe. Produce toxin types: B, E, F. Saccharolytic. Psychrotrophic. In foods: Food intoxication. Food implicated: fermented marine products, dried fish, vacuum packed fish.

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Clostridium perfringens

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Mesophilic anaerobe. Air-tolerant. Rapid growth. Stormy fermentation of lactose in milk. In foods: foodborne non-invasive infection. Food implicated: meat and poultry products.

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Clostridium tyrobutyricum

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Mesophilic anaerobe. Some strain produce toxin type E. In foods: gas formation ("late blowing") of cheeses.

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Clostridium thermosaccharolyticum

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Thermophilic anaerobe. Opt. growth 55-62C. In foods: spoiled canned vegetables

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Desulfotomaculum nigrificans

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Thermophilic anaerobe. Obligate thermophile: min growth temp at 43C or greater. In foods: Hydrogen sulfide spoilage of acid canned vegetables (blackened appearance and rotten egg odor). No swelling of can.

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General characteristics of Fungi

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-Eukaryotic, heterotrophic (saprophytes- dead matter or hypotrophic- parasites).

-Strictly aerobic--> facultative anaerobic (can metabolize without it ex: yeasts). Relevance to foods: growth on surface, probably fungi.

Cell wall contains chitin (like insects) and cellulose (like plants) or both.

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Morphology of Fungi

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Single-celled (eg yeast): generally larger than bacteria.

Dimorphic (ex: Candida): unicellular or pseudohyphae

Multicellular (eg: mold): thread-like strands called hyphae (collectively- mycelium). Septate or non-septate.

Mushrooms- complex

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Mushroom structure

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Front 56

Morphology of foodborne fungi

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Front 57

Propagation of fungi

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Binary fission: rare

Budding: common in unicellular (eg: Saccharomyces cerevisiae).

Elongation of hyphae (at tip): propagation

Fragmentation of hyphae: each piece becomes a new colony

Formation of spores: Asexual or sexual

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Characteristics of Chytridiomycota

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Septate hyphae: None

Asexual sporulation: motile zoospores

Sexual sporulation: oospores

Comments: lower fungi

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Characteristics of Zygomycota

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Septate hyphae: Yes

Asexual sporulation: Non-motile sporangiospores

Sexual sporulation: Zygospores

Comments: lower fungi, not xerophilic, not resistant to heat and chemicals, rare mycotoxin production

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Characteristics of Ascomycota

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Septate hyphae: Yes

Asexual sporulation: Condiospores

Sexual sporulation: Ascospore

Comments: Higher fungi, mostly xerophilic, often resistant to heat and chemicals

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Characteristics of Basidiomycota

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Septate hyphae: Yes

Asexual sporulation: Rare

Sexual sporulation: Basidiospores

Comments: Higher fungi, mushrooms, puffballs, rusts, jelly fungi. No significance to food spoilage

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Characteristics of Deuteromycota

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Septate hyphae: Yes

Asexual sporulation: Conidiospores

Sexual sporulation: None

Comments: Higher fungi. Some are xerophilic, not resistant to heat, some resistant to chemicals, production of mycotoxin is common

Front 63

Asexual fungal spore types

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Conidia or conidiospores- Penicillum spp, Aspergillus spp.

Sporangiospores: Rhizopus spp.

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Sexual Fungal Spores

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Zygospores: spore resulting from the fusion of haploid mating hyphae to produce a diploid zygospore. Eg: Rhizopus spp.

Ascospores: Spores of different mating types in an ascus (pod). Eg: Saccharomyces spp.

Basidiospores: Haploid spores formed on a fungal structure called a basidium. Eg: mushrooms.

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Formation of zygospores

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Front 66

Formation of ascospores (formed in single cell fungi)

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Formation of basidiospores

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Front 68

Beneficial fungi examples

Back 68

Yeast- fermentation

Edible fungi- mushrooms, morels, truffles

Cheese production (surface ripened)

Decomposition in the biosphere- wood-rotting fungi

Symbiosis between fungus and plant

Produce antiobiotics- penicillin produced by Penicillum spps

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Detrimental/Pathogenic Fungi Examples

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Detrimental- spoilage

Pathogenic- plant pathogens (eg: Irish potato famine; loss of chestnut trees); Human pathogens: A. Invasive: athletes foot, ringworm, Candidiasis. B. Toxigenic: mycotoxins

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Mucor characteristics

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Identifying characteristics: nonseptate hyphae, smooth non-striated sporangiospores, produce no rhizoids.

Important properties in food spoilage: Grow on refrigerated meat ("whiskers"). Black spots on frozen mutton, Very common on bread.

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Rhizopus characteristics

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Identifying characteristics: Nonseptate hyphae, umbrella-shaped columellae, large sporangiospore with striated wall. Dark sporangia containing dark to pale spores.

Important properties in food spoilage: Bread mold, watery soft rot of fruits, black spot on beed, bacon, frozen mutton.

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Aspergillus characteristics

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Identifying characteristics: Black, brownish black, purple brown conidiospores. Yellow to green conidia. Dark sclerotia.

Important properties in food spoilage: A. niger: black rot on fruits and vegetables. Yellow, green to black on large number of foods.

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Penicillium characteristics

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Identifying characteristics: P. digitarum: yellow green conidia, P. italicum & P. expansum: blue-green conidia, P. camemberti: gray conidia.

Important properties in food spoilage: Blue/green rots of citrus fruits. Soft rots of apple, pear, peaches.

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Geotrichum characteristics

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Identifying characteristics: Arthroconidia formation, White colonies- colorless conidia.

Important properties in food spoilage: Machinery mold, soft rot of citrus fruits, peaches. Common in dairy products. Some have strong odors.

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Fusarium characteristics

Back 75

Identifying characteristics: Cottony, pink, red, purple, brown colonies. Sickle shaped conidia. Extensive mycelium, colorless conidia.

Important properties in food spoilage: Soft rot of rigs, brown rot of citrus fruits/pineapples, bacon and refrigerated meat spoilage and pickle softening.

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Saccharomyces characteristics

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Identifying characteristics: Multilateral budding, spherical spores, white or cream colonies, typical yeasty odor

Important properties in food spoilage: S. cerevisiae: ubiquitous contaminant, sometimes fermentative spoilage of soft drinks, some strains are preservative resistant.

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Zygosaccharomyces characteristics

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Identifying characteristics: multilateral budding, "dumbbell" shaped asci, 1-4 ascospores/ascus, Bean-shaped ascospores, strong fermenter of sugars!

Important properties in food spoilage: Z. bailii: highly resistant to preservatives, xerophile, capable of growth at aw: 0.8, pH 1.8, heat resistant, ascospores, spoil tomato sauce, mayonnaise, salad dressing, soft drinks, fruit juices etc. Z. rouxii: grow at aw: 0.62

Front 78

Candida characteristics

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Identifying characteristics: Cells are spherical, cylindrical, ovoid, or elongate. Pseudomycelium formation.

Important properties in food spoilage: Common yeasts in fresh ground beef and poultry. C. krusei: preservative resistant, form films on pickles, olives sauces. C. parapsilosis: spoil cheese, margarine, dairy and fruit products

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Most problemative species of fruit concentrates (etc), ketchup, salad dressings, relishes.. etc.

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Zygosaccharomyces bailii and Zygosaccharomyces rouxii.

Why?? Can grow at low water activity, grows over wide range of solute contents. Resistance to preservatives!

Front 80

Behavior of M/O refers to what?

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Their growth, survival and death in foods

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Microbial Growth Requirements

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-Water

-Nutritional needs: carbon source, nitrogen source, growth factors/vitamins/minerals

-Environment: temperature, oxygen presence or absence, pH

-TIME

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Back 82

A. Strict Aerobe- Ex: Pseudomonas

B. Facultative Anaerobe- Ex: Escherichia coli

C. Micro-aeorphilic or Aerotolerant Anaerobes- Ex: Lactic acid bacteria; Leuconostoc

D. Strict Anaerobe- Ex: Clostridium botulinum

Front 83

Facultative anaerobes will grow better under which oxygen condition?

Back 83

Grow faster in the presence of oxygen!

Front 84

Categories Based on Optimum Growth Temp

Back 84

Psychrophiles- love low temperatures (0-20C), grow in the fridge

Psychrotrophs- huge range of temperatures: 5-40C

Mesophiles- 20-40C, mostly 35-37C

Thermophiles- 45-75C

Front 85

Microbial categories based on acid environment

Back 85

Acidophiles- fungi: Zygosaccharomyces

Acid-tolerant: LAB; grow better without acidic environment though

Acid sensitive: Pseudomonas, Clostridium

**Fungi tend to tolerate acid better than bacteria in general

Front 86

You leave two foods out on the counter- one gains weight and the other loses weight. In regards to water activity- which had a lower initial aw? Which is more susceptible to M/O growth? Why?

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The food that gained weight had a lower water activity because its absorbing water vapor from the air; whereas the one that was losing weight had a relatively higher aw- was losing water to the environment (more susceptible to M/O growth- more free water)

Front 87

What are intermediate moisture foods?

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A food product that has a water activity below that which is required for the growth of m/o; or a food containing unavailable water. Characterized as an aw: 0.65-0.90 and general soft texture.

Front 88

Minimum aw for M/O growth

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Bacteria: minimum 0.9 (eg: Clostridium botulinum min is 0.94) Exception: Staphylococcus aureus- 0.85

Most spoilage molds: minimum: 0.8

Most spoilage yeasts: minimum: 0.85. Exception some Zygosaccharomyces spp.

Front 89

In regards to food components- bloating of solid foods or container swelling is implicating what type of breakdown?

Back 89

Degradation of CHOs with CO2 production/other gas

Front 90

In regards to food components- slime is implicating what type of breakdown?

Back 90

Breakdown of complex CHOs (polymerization)- pectin is example.

Front 91

In regards to food components- texture loss is often implicating what type of breakdown? What about rancidity?

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Proteolysis (by proteinases and peptidases). Rancidity= lipolysis by lipases.

Front 92

Parmesan cheese owes its sharp flavor to what

Back 92

Lipolysis by M/O

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Types of food packaging techniques for M/O control

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Air and spoilage- if it needs O2, make anaerobic environment.

Surface vs Bulk- air in headspace; differential spoilage

Food packaging: Headspace (remove oxygen), Canning and Vacuum packaging (no air in headspace or no headspace); Modified Atmospheric Pressure (if you can't get rid of O2- then modify amounts)

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Low-acid foods were categorized by the gov't in regards to what M/O? What pH were they based on?

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Clostridium botulinum- pH 4.6.

Low-acid foods are at a pH between 4.6-5.3 (cheeses) and greater than 5.3- bread, fish, meat, beans, milk, vegetables, egg whites; pH 7.6-9.5: lots of problems!

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What does incidence refer to?

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How M/O got into food.

Unintentional (contamination): What is the source and point of entry into food? What is the level of contamination?

Intentional: intentional inoculation of microbiota into foods (starter cultures or probiotics)

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What are the points of entry of contaminant along the food chain?

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Front 97

Consequences of M/O contamination depend on what?

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-Types of contaminating M/O

-Size of contaminant (eg: cfu/g or ml)

-Metabolic activity

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What does thermoduric mean?

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Tolerates pasteurization temperatures, may find in pasteurized foods. Ex: Some Bacillus spores (B. coagulans); some Clostridium spores (C. putrefaciens); Lactobacillus viridescens; some fungal spores

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Food spoilage during growth of small inocula (effect of cfu/g on likelihood of spoilage)

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Caveats: in conjunction with numbers (population count), spoilage depends on type of M/O and their metabolic activity. Signs of spoilage in milk may appear sooner than they do in other foods.

10^5 cfu/g- start worrying, can hit spoilage population very quickly

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Dairy cattle breeds? Which produce dairy products/milk?

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Holstein-Friesian: main type for milk

Brown Swiss

Guernsey

Ayrshire

Jersey: golden milk color; fat contains carotene; cheddar cheese use to come from them

Milking shorthorn

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Definition of milk

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A fluid secreted by the mammary glands of females for the nourishment of their young; cow's milk used as a food source for humans.

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What pre-harvest factors affect milk microbiota?

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Production practices- is milk collected indoors? Increased chance of contaminants from environment.

Animals activities: diet/exercise..

Animals health

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Harvesting Raw milk

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Preparing cow for milk- clean the udder prior to milking in milking parlor.

Milking- hand milking increases risk of contaminants vs milking machines

Storage on the farm- very important; MUST be refrigerated! Pick up frequency- daily (ideal); otherwise increased M/O growth

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Entry point of contamination in milk (of the udder)

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Contamination outside the udder can contaminate once in contact with milk from teat cistern.

Teat cistern can get contaminated too.

** VERY LITTLE contaminants in raw milk of healthy cows

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Raw Milk Microbiota Sources

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Cows Udder: Foremilk vs final milk: Micrococcus spp. and Staphylococcus albus- Washing and disinfection.

Cow's health status: particularly mastitis- Streptococcus agalactiae, Staphylococus aureus, Escherichia coli, Corynebacterium, Pseudomonas aeruginosa, Klebsiella. Impacts milk biota. Impacts yogurt and cheese industry.

Utensils/Milking machine: general cleanliness and sanitation. Milk stones made, porous, harbors bacteria.

Environment in milking parlor: proximity to maure piles, silos etc. Airborne bacteria of soil sources.

Trucks- ex: ice-cream mix outbreak

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Raw Milk Microbiota Profile

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Total counts:

Aseptically draw milk- 5x10^2-1x10^3 (mostly micrococci)

Milking machine- 1x10^3-1x10^4

Bulk-milk tank- 1x10^4-1x10^5 (mostly psychrotrophs)

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Genera that may be present in raw milk

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Psychrotrophs:

Pseudomonas

Achromobacter

Flavobacterium

Bacillus

Additional biota:

Coliforms

Enterococcus

Lactococcus

Leuconostoc

Lactobacillus

Propionibacterium

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Milk as a spoilage medium

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Milk compositions and M/o requirements- supports the most fastidious microorganisms (eg: LAB).

Milk is 87% water, 4.9% lactose, 3.9% fat, 3.5% protein (casein mainly), 0.7% ash (salt). Has water and fat soluble vitamins. pH ~6.5 and a titratable acid level of 0.17.

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Spoilage before processing of milk causes

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-Heavily contaminated environment (equipment etc)

-Temperature abuse

-Lengthy refrigerated storage

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Main spoilage M/O in milk

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Psychrotrophs

Bacilli and Pseudomonas

Proteolytic and lipolytic bacteria: products yield, flavor defects (cardboard taste, oxidized)

Alcaligenes spp: gram negative, psychrotroph, produces capsules- causes ropiness defect: milk tastes sweet and appears ropy (stringy) in texture.

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Animal Source Pathogens in milk

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Mycobacterium bovis (tuberculosis in children)

M. tuberculosis (tuberculosis)

M. paratuberculosis (Johne's disease in ruminants; Crohn's disease in humans)

Brucella spp- Infectious abortion in animals and brucellosis or undulant fever in humans

Coxiella burnetti- Q fever in humans

LIsteria monocytogenes: listeriosis

Escherichia coli O157:H7: gastroenteritis; hemolytic uremic syndrome

Salmonella spp: gastroenteritis; typhoid fever

Staphylococcus aureus: Intoxication

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Human Source Pathogens in milk

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Streptococcus pyogenes: scarlet fever/sore throat

Salmonella enterica serovar Typhi: Typhoid fever

Shigella spp: Shigellosis

Corynebacterium spp: Diphtheria

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Environment Source Pathogens in milk

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Bacillus cereus: intoxication

Bacillus anthracis: anthrax

Clostridium pefringens: Gastroenteritis

Clostridium botulinum: Botulism

Listeria monocytogenes: Listerosis

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Post-harvest Processing and MO Quality in Milk

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Raw milk- unprocessed

Pasteurized milk- mildly processed

UHT milk- highly processed

Yogurt, buttermilk, sour-cream, cheese- mild processed and fermented

Concentrated, condensed, powdered- milk to high processing