Food2150 Set 2 Flashcards
1
Q
What was Napolean’s primary challenge in the Franco-Russian (Napoleonic) wars?
A
- supplying advancing French army food
- limiting conquest to months they could pillage Russian agricultural resources
- offered reward to anyone who could develop a method to preserve food
2
Q
What are Koch Postulate’s four criteria?
A
- The microorganism must be found in diseased but not healthy individuals;
- The microorganism must be cultured from the diseased individual;
- Inoculation of a healthy individual with the cultured microorganism must
recapitulated the disease - The microorganism must be re-isolated from the inoculated, diseased individual
and matched to the original microorganism.
3
Q
Who was Nicolas Appert?
A
- spoilage organisms were once unbeknownst
- developed an early canning
(Appertization) industry by preserving foods in
glass bottles, forming a continuous seal (preventing anything from entering) - ontents were heating in a pressurized glass vesicle (early retort) to prevent spoilage.
- spontaneous generation disproved
4
Q
Who was Louis Pasteur?
A
- his work was the foundation of hygiene, public health and the germ theory of diseases
- to ensure quality and limit losses of French wine (major national revenue source)
- postulate: fermentation of wine, yeast used to make beer and wine decomposed sugar into ethanol and CO2
- spoilage yeasts convert sugar to lactic acid leading to spoilage, coined the term microbiology
- swan-neck experiment
- foundation of pasteurization, disproving spon. gen.
5
Q
How has mass production changed from the past to today?
A
Past: food grown or hunted (some primary processing), home prep
Today: mass production and feeding, central processing and storage, advance prep, nation/worldwide distribution
- outbreaks less frequent but involve more people
5
Q
What are the goals of food preservation?
A
- Safety - eliminate food hazards
- Extended shelf-life - limit spoilage
- Quality - nutritional and aesthetics
- Availability and Variety
- Convenience
- Favorable economics- minimizing losses and waste
6
Q
What are the causes of deterioration of food preservation?
A
- pests (insect, rodents)
- microorganisms (bacteria, yeasts, mold, viruses, parasites)
- chemical/biochemical reactions (oxidation, enzymatic activity)
- physical factors (light, temperature, moisture, damage by force)
- time !! (deteriorates all food)
7
Q
What is preservation intended to do?
A
- decrease rate of microbial growth (refrigeration)
- stop microbial growth (freezing)
- destroy/inactivate microorganisms (heating)
- restrict access of microorganisms to the food (packaging)
8
Q
What is water activity?
A
- the water available to support microorganisms
- close to 0 for freezing, and so microorganisms cannot move freely
- lower during refrigeration
9
Q
When is lactic acid bacteriostatic and bactericidal?
A
bacteriostatic: @1%
- limits growth of bacteria
bacteriostatic: @2+%
- kills bacteria
9
Q
How does fermentation affect food?
A
- increased shelf life
- enhanced safety
- improved quality + flavour
- fermentation of sugars by bacteria or yeasts to produce lactic acid, CO2, ethanol etc
10
Q
How is yogurt made?
A
- starter culture (contains Lactobacillus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus)
- growth temperature important to enable species (43.3C)
- above 43.3C: Lactobacillus predominates, making it too acidic
- below 43.3C: Streptococcus has too strong of flavour
11
Q
What are some hazards for foodborne illnesses?
A
- illnesses resulting from food ingestion
- biological (bacterial, parasites, viruses, toxins)
- chemical (cleaners, lubricants, antibiotics, hormones)
- physical (glass, woodchips, plastic, metal)
- not just microorganisms !
11
Q
How does organic acids affect food?
A
- Antimicrobial effect due to their undissociated molecules
- pKa range 3.6-4.8: dissocatied lactic acid cannot get through cell wall, in protonated form can move into cell wall
- most foods have pH > 5
- small molecules pass the cellular membrane of microbes
- provide flavour, enhance shelf-life
- lactic, acetic, propionic acid
- @1-2%: prevent spoilage
- effective against gram pos, gram neg, yeats, mols
12
Q
Describe sporeformers
A
- highly resistant form for adverse conditions
13
Q
What are intrinsic parameters: factors affecting microbial growth?
A
- Biological structures -barriers that keep microorganisms out (e.g., fruit
skin) - nutrient content (organism specific – they all need energy, C, N,
certain vitamins, minerals) - pH and organic acids (pH 7, neutral – low, medium, high acid foods
and tolerances, acid production) - moisture content / water activity (aw) – water availability
- antimicrobial constituents
13
Q
Describe typical water activity (aw values)
A
p/pinitial (pi>p)
- free water (1.0)
- some immobilized (0.9)
- bacteria + yeasts stop growing (0.8)
- bacteria + yeasts + molds stop growing (0.7)
- enzymatic reactions slow/stop (0.5)
- chemical reactions slow/stop (0.3)
14
Q
What is a strict or obligate aerobe?
A
- can tolerate a level of oxygen
equivalent to or higher than that present in an air atmosphere
(21% oxygen), and has a strictly respiratory type of metabolism.
14
Q
What are extrinsic parameters: factors affecting microbial growth?
A
- storage temp.
- relative environment humidity
- presence + conc. of gases
15
Q
What is the difference between intrinsic and extrinsic parameters?
A
Extrinsic: food storage, to prevent or slow microorganism growth
Intrinsic: food properties
16
Q
Describe temperature as a factor affecting microbial growth
A
- destroyed by heat - varies by species, can survive but not grow at cold temperatures
- temperature increases, growth rate increases, to an optimum
- Psychrotrophs - optimum growth temperature 20-30oC, can reproduce at temps. of 7oC or below
- Mesophilic, 30-37oC optimum, (body temperature 370C)
- Thermophilic 50-80oC optimum
17
Q
What is a microaerophile?
A
- An organism that is capable of oxygen-dependent
growth but cannot grow in the presence of a level of oxygen
equivalent to that present in an air atmosphere (21% oxygen).
18
Q
What is a facultive aerobe?
A
- an organism that can grow well both in
the absence of oxygen and in the presence of a level of oxygen
equivalent to that in an air atmosphere (21% oxygen)
19
Q
What is a strict or obligate anaerobe?
A
- An organism that is incapable of
oxygen-dependent growth and cannot grow in the presence of an
oxygen concentration equivalent to that present in an air
atmosphere (21% oxygen).
20
What are the HACCP seven principles and what do they do?
- super harsh guidelines to avoid bacteria in prepared foods (avoid outbreaks)
◼Conduct a hazard analysis (biological, chemical, physical)
◼Identify critical control points on flow diagram
◼Establish critical limits for each CCP
◼Establish CCP monitoring procedures
◼Establish corrective actions if limits exceeded
◼Establish record keeping procedures
◼Establish verification protocols
20
What is botulinum and how is it present in canned foods?
- food in containers are anaerobic and thus spore-forming bacteria become active if not processed to a high temp.
- fatal
- anaerobic: grows and produces toxin spore-former grows at pH >4.5
- high acid: sterilize it due to botulism
- low acid: minimal thermal process
21
What is gram negative?
- release fragments of LPS causing fever
- lysed by immune system
21
What is hurdle technology?
- Combining numerous sublethal intrinsic and extrinsic modifications
impede microbial growth
- create an environment that does not support microbial growth
- combine conditions that individually do not stop living, but together do
21
What is gram positive?
- no fever, lipopolysaccharides not broken out
22
Describe foodborne infections going through the intestinal track
* Infectious bacteria are consumed and they colonize the intestinal track.
* During colonization the epithelial cells are damaged
* Damaged epithelial cells are unable to take up solutes
* Osmotic pressure causes water to move from tissues back to the intestinal track
* Damage to the intestinal lining leads to vomiting
* If the bacteria is gram negative it induces a pyrogenic effect causing a fever
due to the presence of lipopolysaccharide
* Examples include Salmonella, Yersinia, Shigella
* Onset ranges from 12hr to 2 days depending on the quantity of bacteria
ingested
23
Describe food borne intoxications and how they come to be
* Bacteria that cause intoxications are those that produce toxins in the food during growth
* Onsets are very fast due to the presence of the preformed toxin
EX: Clostridium botulinum, Staphylococcus aureus, Clostridium
perfringens, and Bacillus cereus
24
What are different ways to preserve food chemically?
- solute addition (water activity control): sugar, salt
- pH control (acids)
- preservatives (nitrate, benzoate (moving away), sorbate
24
Describe water activity control as preservation technique
- reduce it so that there is no molecular mobility
- most common technique
- water activity is colligative: only matters depending on amount of molecule, not its identity
- sugar and salt: bind water available in food, same effect as dying
25
Describe pH control as a preservation technique
- at home: shouldn’t can things of pH below 4.6 as we cannot sterilize it
- pH below 4.6-> conditions for botulism won’t grow
- ex: tomatoes are difficult to can, as they vary: have to double check pH so it is below 4.6
26
What is a biological preservation technique?
- fermentation (addition of antimicrobial contaminants)
27
What is a thermal preservation technique?
- heating + cooling
28
How does heating and cooling differ as preservation techniques?
heating:
- denature proteins in bacteria to stop growing
- kills bacteria, but often causes different sensory attributes
- don’t like to heat: things with free sugars (it caramelizes fast)
cooling:
- stops them from growing (does not denature)
29
What are the 3 types of preservation by heat?
blanching, pasteurization, commercial sterilization
29
Describe blanching as a preservation technique by heat
* MILD heat treatment for fruits and vegetables
* inactivate enzymes prior to freezing
* de-gas products before canning
* wilt vegetables to facilitate packaging prior to freezing or canning
* requires something else to keep it shelf stable (freezing)
* not to remove pathogens or spoilage microrganisms
* deactivates enzymes
* will not brown as the main protein is denatures
30
When is botulism present?
Anaerobic - grows and
produces toxin spore-former grows
at pH > 4.5 (4.6)
- food in containers are anaerobic and thus
spore-forming bacteria become active if
not processed to a high temperature
- solid: surface-in
roll liquids: convection liquid in surface of can is exchanged: heats up uniformly
30
Describe pasteurization as a preservation technique by heat
* MODERATE heat treatment of liquid products
* eliminate pathogenic bacteria
* reduce the numbers of spoilage bacteria (not totally eliminated)
* lasts weeks-months
31
Describe commercial sterilization as a preservation technique by heat
* destroy all microorganisms of commercial significance
and produce a shelf-stable product
* canning: - in-container
* UHT (ultra high temp.) aseptic processing & packaging:
out-of-container, continuous
* long shelf-life
32
What is the hermetic seal?
- prevents contamination of
the material
- rounded lid and sidewall
- side dent: ok to consume, top rim has sent: garbage (hermetic seal broken, potential contamination)
- changed way we put cans together
33
Why do we want to eliminate BPA?
- exhibits hormone-like properties that mimic estrogen effects in body
- banned in EU
- supposedly not used since 2017 in Ca (not true)
34
How do we sterilize food in its can?
* Unsterile food is added to an unsterile
can, sealed and immediately thermally
processed
* Minimum thermal process of the coldest
point, must achieve a 12D process which
means a 12 log reductions
* Hermetic seal prevents contamination of the
material after commercial sterilization
35
Why does microbial death or inactivation never reach absolute 0?
- because the death rate follows first-order reduction kinetics
- 1,0.1,0.01
36
What is the D-value for a bacterial survival curve?
time(temp) (min) required for 1 log reduction of bacteria (nutrient)
- dependent on intrisic and extrinsic propertiesL time it takes to get a log reduction of microorganisms
- have to report temp (temp-dependent), higher T= shorter D value
- D72: D at 72C=1 min, every minute at 72C, there is a log reduction, it would take 12 minutes to get to the 12 log red.
37
What is the Z-value for a bacterial survival curve?
- temperature dependence of the D-value
- The temperature change (oC) required to
change D-value by a factor of 10
- higher T= shorter D, quicker processing of food
D72=1 min and Z=5°C
Indicates that if the processing temp increases from 72 to 77°C, for example, the new D = 0.1 min (or 6 sec) to get 1 log reductions
38
What is the 3 different types of milk pasteurization?
LTLT (ice cream), HTST (milk), UHT (shelf-stable milk)
(low temp, low time) (high temp, short time) (ultra high temp)
39
What is aseptic processing?
* Process the food outside of the package
* Allows for rapid heating and cooling
* Must be packaged aseptically
* food, packaging, environment all have to be sterile or else can be recontaminated
40
What issues does refrigeration cause?
* chill injury in fruits and vegetables (soft apples and dark bananas)
* chill sweetening where starch is slowly converted to sugar
* bread staling where starch changes more rapidly when in the cold than when at room temperature
* cold shortening where freshly slaughtered meat
muscle fibers contract and become tough to chew
41
What does refrigerating food do?
- reduce the rate of microbial growth,
chemical changes and physical changes
