food microbiology: spoilage, preservation, pathogens, fermentation, etc Flashcards
what is spoiled food
food that supports the growth of microorganisms
T or F: spoiled food is unsafe
false; not necessarily. It is undesirable however
define perishable foods
foods that spoil quickly
what characteristics do perishable foods often have
nutrient rich + moist
define semi-perishable foods
not likely to spoil quickly
define non-perishable foods
can be stored indefinitely without spoiling
list some characteristics of non-perishable foods
nutritionally poor, dry, fermented or preserved
list the 2 types of factors that control whether or not microbes will grow in food
intrinsic and extrinsic factors
define intrinsic factors
relate to the characteristics of the food itself
define extrinsic factors
relate to how the food is handled, processed, or stored
list 5 intrinsic factors of food
food composition, water availability, pH, physical structure, presence of naturally occurring antimicrobial substances
describe food composition as an intrinsic factor in regards to food spoilage
nutritionally rich vs poor foods will determine spoilage
what organism will carbs be spoiled by
fungi
what organism with meats/butter be spoiled by
bacteria
describe water availability as an intrinsic factor in regards to food spoilage
foods with low water activity do not support microbial growth
most spoilage bact3ria require an Aw (water activity) of ____
0.91
describe pH as an intrinsic factor in regards to food spoilage
microbes have preferred pH growth ranges
what is the preferred pH range of an acidophile
0.0-5.5
what is the preferred pH range of an neutrophile
5.5-8.0
are fungi acidophiles or neutrophiles
acidophiles
are bacteria acidophiles or neutrophiles
neutrophiles
describe physical structure of food as an intrinsic factor in regards to food spoilage
the presence of an outer covering will decrease the chance of spoilage (ie avocado or egg). Ground meat has more surface area = spoils faster
describe the presence of naturally occurring antimicrobial compounds as an intrinsic factor in regards to food spoilage
eggs contain lysozyme which cleaves NAM-NAG bonds of a peptidoglycan backbone (degrades cell wall)
what are two of the most antimicrobial spices
sage and rosemary
list 4 extrinsic factors that are involved in food spoilage
temperature, storage packing, processing, amount of preservatives
describe temperature as an extrinsic factor in regards to food spoilage
storage temp influences microbial growth. Temps of 4C or less inhibits the growth of most bacteria
describe storage packing as an extrinsic factor in regards to food spoilage
are foods exposed or wrapped?
describe processing of food as an extrinsic factor in regards to food spoilage
foods that are less processed have a greater risk of spoilage
describe amount of preservatives as an extrinsic factor in regards to food spoilage
presence of added preservatives will decrease the risk of spoilage
what is the goal of food preservation
to remove or reduce the population of spoilage and disease causing microbes while maintaining food quality
list the phases on the bacterial growth curve
lag, log/exponential, stationary, death, long-term stationary
during which phase on the bacterial growth curve is food spoilage typically observed? why?
the end of the exponential phase bc they’re the most metabolically active here
list 4 different types of spoilage
souring, bittering, rancidity, putrefaction
what is souring
acid fermentation
what is bittering
alkaline fermentation
what is randicity
the oxidation of fats
what is putrefaction
breakdown of proteins into amino acids
how many microbes per ml or g of product are required for food spoilage to be evident
above 10^6
which phase of the growth curve is most critical when it comes to food preservation? why?
the lag phase + log phase; we want a method that extends the lag phase and delays entry into the log phase
food processing: describe filtration + it’s uses
filters out bacteria/microbes. Used for water, wine, beer juices, soft drinks
food processing: describe low temp + it’s uses
slows the growth of existing microbes but doesn’t decrease the population
T or F: low temps kill microbes
false; it only slows the growth but doesn’t decrease the population
T or F: low temps can slow the growth of all microbes
false; psychrotrophs can withstand low temps
food processing: describe freezing temp + it’s uses
decreases water activity, inhibits bacterial growth
disadvantages of freezing temp in food processing?
can’t do on all food types, freezer burn may occur, doesn’t kill bacteria
food processing: describe high temp+ it’s uses
cooking food will kill most/all microbes that may be present
describe why high temps as food processing don’t always work
exotoxins are heat stable, so the method doesn’t always inhibit everything
food processing: describe canning + it’s uses
another high temp method. Food is heated + high pressure
describe what conditions are used in canning
100C for 20-100 min at 10-15 psi
advantage of canning
everything is killed
disadvantage of canning
there is loss of some food value: some vitamins are heat sensitive. Also food texture changes may occur
food processing: describe pasteurization + it’s uses
another high temp method. Food is heated to a temp that eliminated disease causing microbes and reduces the number of spoilage microbes
T or F: pasteurization significantly changes the nutritional quality of milk
false; it is not a significant change
food processing: how would someone reduce the water activity of food
by drying, adding solutes, or increasing sugar
food processing: describe freeze drying/lyophilization + it’s uses
product is frozen and then dried under vacuum, then stored in an airtight package
describe how changing the acidity of food helps to preserve it
most spoilage occurs at pH of 6-8
changing acidity of food to preserve it: what pH is achieved during pickling
4.6
changing acidity of food to preserve it: how do we change the pH of meat
meat carcasses are sprayed with an organic acid solution
list some chemical preservatives that can be added to food
benzoic acid, parabens, sulfites, ethylene
food processing: describe irradiation
uses gamma (ionizing) radiation. It has great penetrating power and gets rid of all microves
what are bacteriocins
small proteins naturally produced by some bacteria that can exert a negative effect on a closely related bacteria
food processing: what are bacteriocins often added to
ready to eat meats, liquid whole eggs, concentrated fruit juice
food processing: describe the use of a controlled atmosphere+ it’s uses
apples are stored in a high CO2 environment. high CO2 gets rid of ethylene and ethylene ripens fruit. This keeps fruit fresh for longer
food processing: describe the use of modified atmosphere packaging + it’s uses
use of shrink-wrap vacuum technology to remove the oxygen, or use impermeable plastic pouches which are evacuated and sealed
T or F: lots of spices have antimicrobial compounds
true
list the two types of food-related diseases
food infection and food intoxication
how are food-borne infections caused
by ingesting the microbe, and then it grows within the host and causes disease through invasion and/or toxin release (exotoxins)
how is food intoxication caused
the illness is caused by ingestion of exotoxins that are present in the food
which has faster presentation of symptoms: food infection or toxication? why
intoxication has quicker symptoms because the toxin is ingested, not the microbe. Growth of the microbe is not required
list some symptoms of food poisoning
nausea, diarrhea, vomiting, fever, fatigue, muscle cramps
when do food poisoning symptoms occur
2-48 hours after ingestion
list 5 foodborne pathogens
bacteria, fungi, viruses, algae, protozoa
give an example of a fungal derived toxin
aflatoxin
what is aflatoxin caused by
growth in moist grains and nuts
list 2 algae that produce toxins
dinoflagellates and diatoms
describe a dinoflagellate’s toxin effects/how it’s produced
warm conditions –> bloom that results in the formation of a red tide. Shellfish eat the algae and pick up the toxin. Humans eat the shellfish and get paralytic shellfish poisoning
describe a diatom’s toxin effect/how it works
called domoic acid. It can contaminate shellfish and humans can get amnesic shellfish poisoning. It can also accumulate in anchovies or lead to death in marine animals
give an example of a protozoa that produces toxins + what it causes
toxoplasma gondii causes toxoplasmosis
cause of toxoplasmosis?
caused by eating raw/undercooked meat from contaminated animals, or by ingesting food/water that has been contaminated with an infected cat’s feces
symptoms of toxoplasmosis
swollen lymph nodes in neck, aches and pains, headache, fever
list 2 ways to control food-borne pathogens
biocontrol agents or predatory bacteria
describe how biocontrol agents can be used to control food-borne pathogens
its the process of using “living” organisms to combat the growth of pathogens in food (ie bacteriophages)
describe how predatory bacteria can be used to control food-borne pathogens
ie B bacteriovorus preys on other gram neg bacteria. they’re multi-drug resistant, prey on biofilms
how does food fermentation work
microbes are used to create foods that have dif textures, tastes, aromas compared to the natural food. Or they can preserve or stabilize the food, or change the product so after ingestion a change in mental state is noticed (ie beer) The changes occur due to the metabolic end-products of the microbes
list 3 major fermentations
lactic acid, propionic acid, alcoholic fermentation
describe sauerkraut production
shredded cabbage into an airtight container. Add salt to inhibit the growth of microbes on the leaf surfaces. Promotes growth of leuconostoc spp and lactobacillus spp. pH drops and lactobacillus dominates over the other
describe yogurt production
whole milk is centrifuged to get rid of some fat. Milk is pasteurized, add mixed starter culture, ferment, may add probiotics or fruits/flavouring
describe chocolate production
seeds and pulp of cacao pod are removed. Pod is covered with banana leaves. fermentation occurs for 5-7 days and yeasts/bacteria will aid in this. yeasts grow first and they ferment the sugars and produce alcohol. Temp/alcohol will increase so bacteria now dominate. After fermentation the beans are air dried
define probiotic
live organism which when administered in adequate amounts confer a health benefit on the host
