Intrinsic and Extrinsic microbial growth factors Flashcards
what are the 3 extrinsic factors?
Temperature, [gases] and relative humidity
- controlled by storage environment ; where you put the food
what are the 5 intrinsic factors?
1) pH
2) Moisture content
3) Oxidation
4) Content of nutrients / antimicrobial constituents
5) physical structure / barrier
- what you put in the food (controlled by raw material or product formulation)
what is the difference between an intrinsic factor and extrinsic?
Intrinsic factors are controlled by what you put in the food and extrinsic factors are controlled by where you put the food
what is the danger zone?
4-60 degrees celcius
what are the three parameters of temperature in controlling bacterial growth?
T min -minimum T of growth
T opt - optimum T of growth
T max - max T of growth
-specific for the conditions and bacterial species
what is the optimum T for psychrophiles?
< 20 degrees C
-Love cold; adapted to cold environments but not common in foods
what is the optimum T for psychrotrophs? what are examples?
optimum @ 20 degrees C but grow starting at 5
- tolerate cold; adapted to ambient temperature in environment
Listeria monocytogenes, pseudomonas spp.
what is the optimum T for Mesophiles? what are examples?
30-40 degrees C
-love ambient; adapted to vertebrate animals (E.coli and Staphylococcus)
what is the min growth T for mesophiles?
7 degrees C
-no growth at refrigerator T
what is the max growth T for mesophiles?
40-60 degrees
what is the optimum T for thermophiles? what are examples? where is this a concern?
> 45 degrees C
-Love warm; Geobacillus stearothermophilus
-spoilage in tropical climates
what is the optimum T for hyperthermophiles?
> 80 degrees C
-they love very warm
at what T does destruction of most bacterial endospores occur?
> 100 - 121 degrees C
what T are vegetative cells killed?
60 - 80 degrees C
what is the max number of bacteria cells possible on a surface?
10 ^12
- 12D concept
what occurs when there is 10^6 / g bacteria on a food?
there is no noticeable change in food quality
what occurs when there is 10 ^ 9 cells / g in a food?
bacteria begin to grow and the food properties are determined by microbial metabolites
True or False: bacterial endospores are heat resistant?
true
-they are kill > 121 degrees
Explain the survival rate of fungal spores based on T?
most are as heat sensitive as vegetative cells
-killed at 60 - 80 degrees C
does anaerobic storage cause off odours in meat?
no, it causes souring
does aerobic storage cause souring of meat?
no it causes off odours and putrefaction
what is broken down in aerobic spoilage of meat? what bacteria cell count is needed to reach this?
oxidative breakdown of proteins and lipids
-odour and slime after cell count of 10^7
what is broken down in anaerobic spoilage of meat?
fermentation of carbs to lactic acid occurs
-organic acids lead to souring
- souring and slime formation
how does relative humidity affect bacterial growth?
water is needed for microbial growth
-increased humidity will allow for growth (high Rh)
what occurs with a high Rh and refridgeration?
condensation
what makes blue steak safe to eat?
the physical barrier of the inside the meat to contaminants allows for the muscle of the meat to be sterile
what determines a microorganisms ability to utilize different energy sources?
the type of enzymes it produces
what kind of enzymes are needed for starch utilization?
amylolytic enzymes
what kind of enzymes are needed for protein utilization?
protease
what kind of enzymes are needed for lactose utilization?
beta- galactosidase
what does it mean for an organism to be fastidious?
they require sugars, amino acids and vitamins to utilize energy (lactic acid bacteria)
what defence system do egg whites and saliva have in common?
they contain lysosomes to hydrolyse cell walls
what systematic defense system is common in garlic, onions and mustard?
they have glucosinolates that generate isothiocyanates to oxidise thiol groups in proteins
what system defense in common in milk?
lactoperoxidase system that react with thiol groups to reduce oxidative stress
what pH resists most pathogen growth?
< 4.5
what are the exceptions to the pathogens that grow <4.5 pH
Salmonella and E.coli = 4.0
S. aureus = 4.2
at what pH do bacterial endospores not germinate at?
< 4.5
what are the exceptions to the bacterial endospores that grow at a pH < 4.5?
Alicyclobacillus acidoterrestris
- contributes to spoilage of fruit juices
what microorganisms commonly grow at a pH < 4.5?
lactic acid bacteria, yeasts and mould
what is considered a high acid food? and lolw acid?
< 4.5 = high acid
> 4.5 = low acid
how do we treat high acid vs low acid spores?
high acid - pasteurize
low acid - pasteurize and refrigerate or sterilize to kill spores
are the effects of organic acids (lactate and acetate) or pH stronger?
the inhibitory effects of organic acids are stronger
at what pH do mold/yeast grow?
pH 1.5 - 3.5
at what pH does Acetobacter spp. grow?
pH 2.4
at what pH do many Lactobacillus spp. grow?
pH 3.5
at what pH does E. coli, Salmonella and S. aureus grow?
pH 4.0 - 4.2
at what pH does C. botulinum grow?
pH 4.5 - 5.0
at what pH does Vibrio parahaemolyticus grow?
pH 4.8
how does ripening affect pH?
it can increase pH by 0.5 units upon ripening
what effect does microbial metabolism have on acidic and fermented foods?
causes alkalinization
what is the range of Aw that most foods fall into?
0.7 - 1.0
what 2 things can you add to reduce water activity? why?
10% sucralose
10% NaCl
-sugar and salt are both hygroscopic so the addition of them allows water to bind to these molecules and reduce the free water available for microbial growth
at what Aw is crispness lost?
> 0.5
at what Aw is there rapid lipid oxidation?
0 - 0.2
at what Aw do browning rxns occur?
0.2 - 0.6
at what Aw does mold growth begin?
0.6
at what Aw does yeast growth begin?
0.8
at what Aw does spoilage bacteria growth begin?
0.9
- however, most are inhibited below 0.93
at aW of 0.92 or less what occurs?
inhibition of growth pathogens and toxin produced by S. aureus
what are halophiles or halotolerant bacteria? at what aW do they grow?
salt loving or salt tolerating bacteria
- they grow at an aW > 0.75
-found in soy sauce
what are osmotolerant yeasts? at what aW do they grow?
yeast that tolerates a high [inorganic compounds]
-grow at aW > 0.61
what are Xerophilic molds?
at what aW do they grow?
molds that tolerate dry conditions
-grow with aW > 0.61
what 3 methods can decrease aW?
1) drying
2) dry salting
3) brine solution
how long should food being sold be able to go without going bad?
3 weeks
1 week- distribution
1 week -shelf life
1 week -in consumer house
what foods are common in an oxidizing environment? why?
fruit, veg, fat, wine, beer, meat and any processed foods w added fat
- oxidizing environments are created when O2 is available to oxidize the food and cause a loss of electrons
what foods are common in a reducing environment? why?
fermented foods, canned/ vacuum sealed, foods high in antioxidants and foods stored in modified atmospheres
- reducing atmospheres do not have O2 available which causes a gain in electrons and aids in preservation
what microorganism is able to grow in environments with high redox potential?
Clostridia
what are the guidelines for cooling cooked meat?
to avoid the danger zone (4 - 60 degrees C) meat should be cooled down to 4 degrees C within four hours of cooking period
- should be cooled to 21 degrees C within 2 hours to prevent multiplication of bacteria
what is the hurdle concept for bacterial growth?
Instead of relying on one preservation method a combination of methods is applied. Each hurdle weakens or stresses bacteria, yeast, or molds, and the combined effect creates an environment where microbial growth is significantly limited
