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NUFS 363 > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

Extrinsic factors

A

properties of the environment “where you put the food”

  • temperature
  • presence and concentration of gases
  • relative humidity
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2
Q

Intrinsic factors

A

properties of the food “what you put in the food”

  • pH
  • aw
  • oxidation reduction potential
  • content of nutrients or antimicrobial constituents
  • physical structures
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3
Q

Psychrophiles

A

love cold

optimum

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4
Q

Psychrotrophs

A

tolerate cold

optimum >20, can go at

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5
Q

Mesophiles

A 
love ambient 
optimum ~30-40
e.g. e coli and s aureus
no growth at refrigeration temp
most food borne pathogens are mesophiles - survive in intestines
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6
Q

Thermophiles

A 
love warm
optimum >45 
eg. Geobacillus stearothermophilus
relavent for spoilage in tropical climates
have heat resistant spores
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7
Q

Hyperthermophiles

A

love very warm
optimum >80
not relavant in foods

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8
Q

Danger Zone

A

4.4-60 degrees - unsafe
optimum temperature for microbial growth of mesophiles
if you keep foods hotter than 60 and less than 4, growth of most pathogens is inhibited

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9
Q

Foods not to refrigerate

A 
climacteric fruits (tomatoes, melons, bananas)
oil, honey and bread
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10
Q

How to store a ham sandwich?

A

store the whole thing in the fridge because the safety issue of the ham is more important than the spoilage issue of the bread

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11
Q

Bacterial endospores

A

Heat resistant
cannot be destroyed by household heating
need to be controlled by pressure cooking (>121 degrees) or combined with low pH etc.

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12
Q

Fungal spores

A

most are as heat sensitive as vegetative cells
will usually be destroyed by cooking or pasteurization
exceptions** byssochlamys fulva, B nivea, Aspergillus fischeri which can withstand pasteurization (fruit juices)

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13
Q

Gaseous environment ambient conditions

A

20% o2

80% N2

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14
Q

Modified Atmosphere conditions

A

take away 02
- vacuum packaging
- N2 inhibits growth of aerobic organisms
add Co2
- inhibits growth of aerobic organisms but NOT LAB

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15
Q

Aerobic Spoilage

A 
ex. pseudomonas sp..
can grow (in meat)
metabolizes proteins - smell containing N or S
odor and slime after 10^7 is reached
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16
Q

Anaerobic Spoilage

A

ex. LAB
metabolizes CHO - souring
some strains can convert amino acids - occasional S odor

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17
Q

3 magic numbers in food micro

A

10^6 - over this number will notice activity (dangerous because some infective doses are less than this)
10^9 bacteria will grow to this in food
10^12 max number of bacterial cells (12 d concept)

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18
Q

12 D concept

A

requires heating process to reduce the bacterial count by 12 log cycles.

ex. if you start at 10^6, and you heat for the time to reduce by 12 log cycles, you would have a population of 10^-6, which would provide a safe product.
- used in canning to ensure no C. botulinum

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19
Q

Can you store spinach in an anaerobic condition?

A

No - will wilt. Can add Co2 to decrease microbial growth, without suffocating the leaves

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20
Q

Examples of physical barriers (intrinsic factor)

A

banana peel, egg shells - prevents organism from getting to the nutritious part of the food
butter - makes an emulsion that results in small water droplets - must be small**

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21
Q

Antimicrobials - plant/animal defence systems - examples (intrinsic factor)

A

e. g. lysozome in egg white - hydrolyzes cell wall and protects if organism gets past the shell
e. g. lactoperoxidase in raw milk - not sufficient on its own
e. g. isohumulones (hops) in beer - also added for flavor - permeabilizes bacterial membranes
e. g. glucosinolates in garlic, onions, and mustard -

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22
Q

Most pathogens do not grow at a pH below…

A

4.5
exceptions - salmonella, e coli. and s. aureus, LAB
- if ph 4.5 pasteurize, refrigerate or sterilize to kill spores

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23
Q

min water activity examples

A 
pseudamonas 0.97
e.coli and salmonella 0.96
c botulinum 0.94
most spoilage bacteria 0.9
s.aureus 0.86*

min aw for growth is dependent on the solutes** sugar solutions are less inhibitory than salt solutions at the same aw.

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24
Q

halophiles and halotolerant bacteria

A

loving salt and tolerating salt

aw >0.75

25
Q

osmotolerant yeasts

A

tolerate high concentration of organic compounds

aw >0.61

26
Q

xerophilic molds

A

tolerate dry conditions

aw. >0.61

27
Q

How is aw decreased?

A
  1. drying
  2. dry salting (pulls water out - meat)
  3. brining (osmotic dehydration) (put in high salt or high sucrose concentration)
28
Q

Growth Inhibition

A

bacterial growth is static but organisms remain alive

  • cold, low aw, low pH
  • enough for a pathogen with a high infective dose (i.e. clostridium perfringens)
  • NOT enough for a pathogen with a low infective dose (i.e. ehec)
  • bacteria resume growth when conditions change (i.e. temp abuse)
29
Q

Microbial Death

A

Elimination of bacteria and spores
- heat, pressure, radiation, chemicals (low pH)
prevents regrowth during storage and ambient conditions

30
Q

Pasteurization

A
  • 60-80 degrees (less than 100)
  • kills vegetative and fungal spores
  • milk target organism coxiella burnetti
  • alkaline phosphatase has a similar z value to pathogens - if you can detect its activity (like in raw milk), then you know that heating was not sufficient
  • low temp holding 63 degrees for 30 minutes
  • high temp short time - 72 degrees for 15 seconds (typical for milk
31
Q

Commercial Sterilization

A

121 degrees

  • typical for canning is 121 for 15 mins
  • kills vegetative bacterial cells, fungal spores, and endospores of bacteria that grow at ambient temperature
  • spores don’t have a metabolism so can still survive in a dry environment**

acid foods pH 4.5
- need heat inactivation of endospores

target organisms

  • food safety - clostridium botulinum (most heat resistant pathogen and produces the most lethal toxin)
  • food spoilage - C sporogenes, geobacillus stearothermophillus etc. more resistant than C botulinum so if you know you don’t have spoilage you also know the food is safe**
32
Q

Process that are not predominantly aimed at food preservation

A

cooking

  • 100 degrees, meal prep; kills bacterial cells and fungal spores
  • creates optimum growth conditions for clostridium perfringens and s. aureus

blanching

  • 70-80 degrees
  • prior to canning, inactivates enzymes and removes o2

drying/concentration

  • 40-100
  • evaporates water (dry heat does NOT kill bacteria)
33
Q

Benefits vs. Disadvantages of Thermal Preservation

A

Benefits

  • quick, easy, cheap
  • reference process, well understood and good safety record
  • inactivates enzymes
  • changes in flavour/texture are usually accepted by the consumer
  • maintains most nutrients and vitamins

Disadvantages

  • energy requirement
  • changes flavour (still accepted by consumers)
  • destroys some vitamins (
34
Q

Shoulder effect

A

uneven heating of the food or clumping of organisms so that they are not evenly exposed to heat

35
Q

Tailing effect

A

heat resistant mutants

36
Q

Thermal preservation won’t work without __?

A

Water.

  • as soon as you take away water, pasteurization and sterilization lose all of their effectivity
  • dry vegetative cells have high heat resistance (i.e. salmonella on almonds, potato chips, peanut butter)
37
Q

Sublethal Injury

A

When cells are not quite dead yet.
Heating may injure but not kill cells.
- unable to grow on selective media
- given time, they restore viability (extended lag phase)
- cell injury is represented by the growth difference between the non selective media line and the selective media line
- difference in lines reflects the level of selection media - important for industry to keep in mind (storage allows for repair)

38
Q

Fo value

A

time to reduce population of target pathogen by given amount at 121 degrees

39
Q

Alternatives to thermal processing

A

microwaves, ohmic heating, microfiltration, aseptic packaging, high pressure, pulsed electrical fields, ionizing radiation

40
Q

Microwave pros and cons

A

pros - rapid, broad spectrum of activity (bacteria, yeast, viruses, told)
cons - thermodynamic gradients, water activity, survival of endospores
** needs h20

41
Q

Micro filtration pros and cons

A

pros - no change in product, extended refrigeration shelf life
cons - less effective removal of bacteria than pasteurization, costly

42
Q

pulsed electrical fields pros and cons

A

pros - retains product quality, short treatment time, heating enhances microbial effects
cons - low aw has a protective effect, ineffective against enzymes and spores

43
Q

Ionizing radiation pros and cons

A

(x rays, gamma rays, beta particles) - destroys the DNA

pros - control achievable, death/destruction of microbes
cons - dose not effective for endospores, consumer acceptance, side effects (lipid oxidation)

44
Q

Food Additive

A

affects the characteristics of the food, substance part of the food, label declaration

45
Q

Processing Aid

A

no impact on food characteristics, not part of the food, negligable residues of substance in food, no label declaration
e.g. lactic acid bacteria

46
Q

Functions of weak organic acids in foods

A
  • flavour (taste and odor)

- pH modification

47
Q

How are organic acids different from a low pH (protons)

A

Weak organic acids can cross the cytoplasmic membrane whereas protons cannot

  • protonated form i.e. acetic acid vs deprotonated form acetate
48
Q

Why do bacteria mind transport of protons into the cell?

A

1) metabolic energy - influx of protons decreases intracellular pH, which wastes energy
2) low intracellular pH - enzymes of most mesophyllic bacteria don’t function at a low pH

49
Q

organic acids are good preservatives only if…???

A

the pH is equal to or less than the pkA

  • most organic acids have a pKa of 4.2-4.8, which means they function well in acidic foods but not in neutral foods (except parabenes which don’t have a pkA - work well at high pH)
  • the catch ** most organic acids have a characteristic smell at concentrations that are effective against bacteria and fungi
50
Q

Pros vs. Cons of Organic Acids

A

pros

  • wide applicability (bacteria, yeasts, moulds, endospores when combined with pH)
  • generally accepted by consumers
  • work in tandem with pH

cons

  • pKa is a critical factor - may prevent use in food depending on pH
  • may negatively affect flavour profile
  • “clean” label and fewer additives may be preferred alternatives
51
Q

Sulfites

A

SO2, NaSO2, etc
more effective at low pH
used in wines to control yeast or fermentation

52
Q

Nitrites

A
  • inhibit the outgrowth of C botulinum in meats
  • works better in foods with a low pH (activity increases with decreasing pH)
  • irreversibly inhibits the iron suffer cluster in enzymes found in clostridia that are essential for growth
  • very selective ingredient** inhibits clostridia but other organisms may still grow
  • risks - potential for carcinogenic nitrosamine formation, but the alternative is worse (can be controlled by adjusting usage levels and addition of ascorbic acid)
  • even natural meats have nitrites - celery extract contains nitrates which when cultured in the right bacteria convert to nitrites
53
Q

Allowable limits of nitrites in Canada

A
  • 150 ppm

- 120 ppm in bacon - bacon can reach a higher temperature in its fat content, which favours nitrosamine formation

54
Q

Bacteriophage processing aids

A
  • viruses that kill bacteria
    very specific targets **
  • phage cocktails - 5-10 different phages to control all of target species
    use level 10^8 pfu/g = 3 log kill
    phage MUST come into contact with the bacteria**
    approved for use to control L monocytogenes
    considered “organic”
55
Q

pros and cons of bacteriophage

A

pros - considered processing aids so don’t need to be labelled, have no impact on quality (small and have no metabolism)

cons - don’t move - an issue in solid foods because they might not come into contact with the bacterial cell

56
Q

Bacteriocins

A

antimicrobial peptides or proteins produced by bacteria

  • classified according to structure
  • class I: lantibiotics (containing lanthionine, e.g., nisin)
  • class II: small heat stable peptides
57
Q

Nisin

A
  • class I bacteriocin
  • 5 ring structure
  • produced by Lactococcus lactis spp. subs lactis
  • used in milk, cheese, cans, alcohol, fermented sausage (partial replacement of nitrite), fish, eggs
58
Q

control of viruses

A
  • don’t multiply in food - want to keep them out of food supply*
  • much more resistant to environmental stress and inactivation treatments than bacteria
59
Q

Norovirus

A

12-72 h incubation, symptoms last 1-3 days
diarrhea, projectile vomiting, nausea, abdominal cramps
self limiting and relatively mild
more severe for elderly and immunocompromised
outbreaks in close contact settings** eg. cruise ships, residences, nursing homes
- infective dose is EXTREMELY LOW 18 particles - extremely contagious
- extremely stable at room temp/freezing
- extremely resistant to disinfection
- can shed for 3-4 weeks
- high rate of mutation - can get it again even if gotten it before
- high risk foods include berries, and produce (contaminated H2o; food handler contamination - typically eaten raw), seafood (oysters, clams, muscles - bivalves filter water and concentrate microorganisms), ready to eat foods

NUFS 363 (2 decks)

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