Lecture 1: Food is an Ecosystem Flashcards
explain the general cycle of a pond ecosystem
- producers (rooted plants) as well as phytoplankton
- consumed as food-nutrients by primary consumers ie zooplankton
- then primary consumers are cosumeed by secondary consumers ie fish
- secondary consumers consumed by tertiary consumers ie. turtle.
- when any consumer dies, secretes feces etc then it gets broken down by bacteria & fungi creating sediments
- sediments may then be reintroduced and can contain dissolved chemicals
what is an ecosystem?
is a series of interactions between the environment and the organisms that inhabit it
food ecosystems like all ecosystems are impacted by?
the generation and utilization of energy
T or F: the human & animal GI tracks are also ecosystems
True
T or F: food ecosystems affect host ecosystems and may result in illness
T
food ecosystems are composed of what 2 factors? explain
They are composed of intrinsic and extrinsic factors. Intrinsic factors are factors that are inherent to the food’ (pH, water activity, nutrients) and extrinsic factors are external to the food (temp and gaseous atmosphere). Both factors may change over time as bacteria grow and produce bi-products.
What are the 4 main bacterial growth and division requirements?
- bacteria must have a carbon for building the array of chemical substances of which they are composed.
- bacteria must have source of energy for living (catabolism)
- bacteria must have a source of electrons to be used in energy conservation and biosynthetic reactions.
- bacteria must have an electron acceptor
how can bacteria be classified based on their ability to obtain carbon?
- Autotrophic: carbon from CO2 trough carbon fixation
- Heterotrophic: carbon from organic compounds
- Mixotrophic: can combine auto and heterotrophy
what are the different types of ways bacteria can perform catabolism (obtain energy)?
- chemotrophic: energy is obtained from external chemical compounds
- phototrophic: energy is obtained from light.
autotrophic
carbon obtained from CO2 trough carbon fixation
Heterotrophic
carbon obtained from organic compounds
Mixotrophic
Can combine auto and heterotrophy
What are the two different ways bacteria can obtain a source of electrons to be used in energy conservation and biosynthetic reactions?
- lithotrophic: reducing come from inorganic compounds
2. organotrophic: reducing equivalents come from organic compounds
use oxygen as a terminal electron acceptor
aerobic organisms
use organic carbon as a terminal electron acceptor
fermentation ie anaerobes
what are facultative anaerobes?
organism can grow with or without oxygen
what are examples of unusual forms of fermentation?
succinate and oxalate
succinate and oxalate fermentation are very high/low energy yielding
low
what are the other important types of anaerobic terminal electron acceptors?
Denitrification- nitrate as an electron acceptor
Sulfate Reduction – sulfate as an electron acceptor
Acetogenesis – CO2 as an electron acceptor
Ferric Iron, Manganic ion, and Arsenate can also be used as terminal electron acceptors
lactic acid bacteria
produce relatively large quantities of lactic acid from carbs
ex of LAB
lactobacillus in yogurt
proteolytic bacteria
hydrolyse proteins in food because they produce extracellular proteinases (clostridium botulinum)
lipolytic bacteria
hydrolyse triglycerides because they produce extracellular lipases
how are bacteria grouped by their ability to grow a specific temperatures
thermophillic, thermoduric, psychotrophic and cryophillic bacteria
term given to bacteria that can survive high salt concentrations (>10%)
halophillic
aciduric
able to survive low pH
osmophilic
able to grow at a higher osmotic pressure
Bacteria that are able to grow at 50∘C and above
thermophillic
able to survive pasteurization temperatures
thermoduric
psychotropic bacteria
able to grow at refrigerated temps (less than 5 deg C)
cryophillic bacteria
able to grow at freezer temps ( less than 0 deg C)
example of a spore former
clostridium botulinum
coliforms are used an index for __
sanitation
used as an index for sanitation, presence indicates fecal contamination
fecal coliforms
T or F: enteric pathogens can cause gastrointestinal infection
True
relative abundance of a specific type of microorganism will depend on what 2 factors
intrinsic and extrinsic factors
if growth can occur the ___ number of microbes in the food will be the ones that can grow optimally in the conditions provided
optimally
explain the food ecosystem in raw and ready to eat meats
Following slaughter carcasses of animals may contain several types of bacteria coming from skin, hair, feathers, and the GI track
As well as from the slaughter facility
Carcasses immediately after slaughter contain 10 1-3cells/square inch (not that many), but this can contain pathogens at low levels (i.e. Salmonella is carried in the GI track of most birds)
Because meat is stored chilled psychrotrophic organisms are the main issue (unless temperature abuse occurs) Listeria is psychrotrophic
Ground meat can have 104-5cells/g
Heat processed meats (lunch meat) also contain several chemicals to reduce bacteria and have a shelf life of 50 days or more
These products can be stored anaerobically causing psychotropic facultative anaerobes to dominate.
Heat processing kills most bacteria, microbial level can be as low as 10 1-2cells/g
because meat is stored chilled ___ bacteria are the main issue
psychrotophic
an example of psychotrophic bacteria is
Listeria
____ meats (lunch meat) also contain several chemicals to reduce bacteria and have a shelf life of 50 days or more
Heat processed
Heat processed meats can be stored ___ causing _____ to dominate
- anaerobically
2. psychotropic, facultative anaerobes
Explain the bacteria introduction-ecosystems in raw and pasteurized milk.
Raw milk (mostly) comes from cows, which are a source of microorganisms, normally raw milk contains <103cells/mL, but this can be much higher in cows with mastitis
Milk is high in carbohydrates (lactose) and protein both of which are great sources of carbon and energy for microbial growth
Before pasteurization milk is refrigerated to preserve its quality (psychrotrophs still grow, so quick pasteurization is desirable)
Pasteurization kills all pathogens, and most other microbes, but milk quickly becomes contaminated again from equipment, handling, and air. The standard for pasteurized milk is 104cells/mL
After pasteurization milk contains thermodurics that survived pasteurization and bacteria that enter following treatment
Psychrotrophs are responsible for spoilage in non-temperature abused milk
Normally raw milk contains < ___ cells/ml but this can be much higher in cows with what condition?
- 10^3
2. mastitis
what are the main sources of carbon and energy for microbial growth in milk
carbohydrate lactose and protein
T or F: Pasteurization kills all pathogens and most other microbes. Once milk is pasteurized it is safe forever.
False. Pasteurization kills all pathogens, and most other microbes, but milk quickly becomes contaminated again from equipment, handling, and air.
The standard for pasteurized milk is __
10^4cells/mL
___ are responsible for spoilage in non-temperature abused milk
Psychrotrophs
After pasteurization milk contains ____ that survived pasteurization and bacteria that enter following treatment
thermodurics
Ecosystem of fish and shellfish
Fish and shellfish are harvested from aquatic environments
They are generally rich in protein and low in fat and carbohydrates
The microbial population on fish comes directly from harvest environments, which varies greatly based on water pollution and temperature (i.e. Vancouver oysters)
From marine environments (high salt) several microbes in fish are halophiles
Fish harvested from water polluted with human waste can contain several varied pathogens (Vibrio cholerae)
Microorganisms can grow rapidly in fish because of high water availability, the pH of the tissue, and the availability of carbon and nitrogen
Microorganisms can grow rapidly in fish because of what factors?
high water availability, the pH of the tissue, and the availability of carbon and nitrogen
From marine environments, several microbes in fish are?
halophiles
Fish harvested from water polluted with human waste may contain
several varied pathogens like vibrio cholerae
What conditions render fruits and vegs optimal for the growth of bacteria, yeast and mold?
storage at room temp, high carbohydrates, pH values between 5-7 for veg (fruit have pH below 4.5)
sources of contamination for fruit and veg include
soil, water, air, animals, insects, birds, equipment, harvesters, ect.
Definition of canned food
hermetically sealed containers that have been given heat treatment to obtain commercial sterility
what is an important factor in canned food and why?
pH becomes an important factor in canned foods
If pH is lower than 4.6 pathogenic mesophiles cannot germinate and produce illness causing toxins (Clostridium)
If pH is above 4.6 pathogenic mesophiles are not an issue, but if cans are temperature abused (stored over 40C) thermophilic spores can germinate and cause spoilage
T or F: Staphylococcus can grow in canned food
False. However, it’s toxins can survive the canning process, therefore if Staphylococcus grows in food pre-canning and produces toxin, the toxin will survive the process and cause food poisoning following the consumption of the product
