Food Microbiology Unit 3 Flashcards
What are characteristics of spoiled food?
Poor taste, appearance, smell, or texture
organoleptically detectable
What causes finfish to have a high bacterial count?
Trawling, dragging the fish through the water on the ground which kicks up bacterial from the floor. Close proximity of the fish also cause them to poop on each other and contaminate that way.
line fishing is much more sanitary
What determines the quality of shrimp?
Because shrimp are filter feeders the quality of the water that they live in matters substantially.
What is the order in which bacteria will use resources in meat?
Carbohydrates _> Proteins _> Lipids
What is the primary spoilage microorganism in foods that are vacuumed packed or packed in modified atmospheres?
Lactic acid bacteria
What happens to meat from animals that have been stressed when it spoils?
The meat spoils more quickly because there is less glucose which means more lactic acid
-lactic acid makes meat sour
What is the primary spoilage organism for dry (low water activity) foods?
Fungi
Dry=fuzzy
slimy = bacteria
-Fungi tolerate salty and sugary environments
What are three reasons that ground (comminuted) meat spoils
- Higher initial microbe load due to lower quality product for grinding
- contamination during processing
- effect on muscle tissue; introduces more oxygen
Three types of spoilage i processed meats
- formation of slime
- development of SOUR taste
- greening from the production of hydrogen sulfide
What causes cured meats to spoil?
they contain lactobacilli and micrococci, which are both aerobic and tolerate low water activity, that will spoil the meat.
What are the methods used to preserve muscle foods?
GMPs, removal of contaminants from carcasses through rinsing with water (by immersion or by spraying), refrigeration (storage under vacuum or modified atmosphere), and irradiation
Can spoilage organisms utilize the fats and proteins in milk?
Yes, although they cannot use whey. They can use caseins, but not whey because the whey is soluble.
What inhibits the growth of spoilage microorganisms in yogurt and cheeses?
a LOW pH
What causes yogurt and cottage cheese to spoil?
yeasts and molds. The low acid inhibits the bacteria, but not the yeast and molds
What are the primary spoilage bacteria in milk?
Pseudomonas (psychotropic), coliforms, LAB, Bacillus, clostridium
What are a plants defense against spoilage microorganisms?
outer layers including cuticle, epidermis, and cell wall. Waxes
What are the microflora of vegetables?
Bacteria, yeasts, and molds
Why do fruits spoil less readily than vegetables?
fruits have a lower pH, higher sugar content, lower water activity, thicker epidermis, and higher concentration of organic acids
How are grains and grain products preserved?
Low water activity
Are the populations of microbes decreased in processing of grains?
yes, from drying
Origin of microflora: Meat poultry finfish shellfish
- hide, hooves, and hair
- feathers, skin, and feet
- environment, trawling
- environment, filter feed
Proteolytic enzyme activity
- only occurs in populations >10^8 CFU/cm
- digestion of protein, comes before lipolytic
- production of the protease enzyme doesn’t occur until the late log phase
Lipolytic enzyme activity
- oxidative rancidity with unsaturated fatty acids
- rate is influenced by the proportions of unsaturated fatty acids in the fat
- unlikely to occur until all the glucose in the muscle is depleted
Adipose tissue
- insoluble fat, cannot be used until its broken down and emulsified
- low levels of carbs in adipose tissue means that spoilage odors are detected from lower numbers of bacteria .
- spoilage of fat before lean tissue is unlikely
Anaerobic conditions
- lactic acid bacteria
- growth rate is lower is considerably lower than those in aerobic environments
Cooked muscle foods
cause by bacteria that survive the heating process, psychotropic and micrococci species
Prevention of spoilage
prevent the growth or select for less offensive species
- GMPs
- TEMPERATURE
- vacuum and modified atmosphere
Dairy fat
Few microorganisms can utilize fat as an energy source
- fat globules are surrounded by a protective membrane
- must rely on proteolysis or lipolysis to obtain energy
Lactose
many microorganisms cannot utilize lactose
-not sufficient amounts of glucose in milk to be a good growth medium
proteins
two types; casein and whey.
Casein is readily susceptible to proteolysis but why is not as much.
-Lactoferrin binds to iron and inhibits microbial growth
— lactoperoxidase
Liquid milk concentrates
-so not have sufficiently low water activity to inhibit spoilage and so products must be canned or refrigerated
Milk powders
sufficiently low water activity to inhibit spoilage
Butter
unsalted butter is usually made from acidified cream and relies on low pH and refrigeration for preservation.
-growth of psychotropic bacteria only occurs on butters made from sweet cream
Psychotropic bacteria
comes from soil, water, animals, and plant material
- pasteurized milk products become contaminated with psychotropic bacteria by exposure to contaminated equipment or air
- Pseudomonas spp. most rapid, 3 degrees C
Fermentative nonspore formers
most are in the lactic acid producing or coliform group.
-coliform’s Can spoil milk but this is rarely the cause, it’s usually the lactic acid producing bacteria.
Spore forming bacteria
- usually are present in milk products packaged with little chance of contamination aka aseptically packaged foods like boxed milk and canned milks
- clostridium are present in raw milk but in such low numbers that you’d have to enrich the solution to get anything to count
Yeasts and mold
grow well as low pH
- cultured milks such as yogurt and cottage cheese are prone to yeast spoilage
- mold spores do not survive pasteurization
- Yeasts are able to produce proteolytic or lipolytic enzymes
Vegetable spoilage
active spoilage by microorganism infecting plant
- passive spoilage by a wound
- soft rot is best known type
- age reduces resistance to infection
- senescence = accumulation of degradative enzymes
- bacteria more frequently are the initial spoilage source because bacteria grow faster than yeast and molds
- history of the land
- reduction of senescence requires carbon dioxide
- canned vegetables require temps exceeding 120 degrees C
Five degradative enzymes
cellulase, protease, pectinases, phosphatidases, dehydrogenases
Fruits
most often spoiled by yeasts or molds because not as hospitable of an environment for bacteria
- generally require less severe treatments than vegetables
- canned fruits being processed at 85 to 90 degrees C
Grains
Have a water activity level below 0.65 which inhibits microbe growth
- xerotolerant molds can grow on dried grains
- mold spoilage results in mycotoxins
Beneficial effects of fermentation
adds flavor and carbonation, alters texture, increases nutrient bioavailability
Homolactic fermentation
process When the only product is lactic acid
-glucose to pyruvic acid, “best” pathway because of ATP yield
Entner-Doudoroff
lactose fermentation, uses ‘wasted’ galactose that couldn’t be used by organisms using homolactic fermentation
heterofermentative
releases carbon dioxide molecule, generates one ATP, uses five carbon sugars (pentose) that other organisms cannot use.
What determines which fermentative path an organism uses?
whatever it can digest
Dairy fermentation cultures
starter cultures of LAB are added after pasteurization so that they don’t have to compete with other bacteria. This means that you can control the acidity of the milk product; consistent and predictable results
- Secondary cultures are added to influence flavor and texture
Generic scheme for dairy fermented products
- Clarification,
- formulation (addition of salt, seasonings, or milk solids)
- Heat treatment
- Homogenization
- Inoculation and incubation
- cooling, formulating ,and packing
Importance of acidification in dairy processing
affects moisture control, protein retention, mineral loss, protein hydration, and interaction with protein molecules
Products of secondary fermenters
acetic acid, acetaldehyde, and diacetyl (buttery flavor)
Veggie fermentation steps
select veggies
- pretreat by blanching, peeling, or cooking
- place in fermentation vessel
- cover with brine and create anaerobic conditions
- aging
role of salt in sauerkraut
draws out liquid and prevents other microbes from growing
four stages in sauerkraut fermentation
- fermentation starts: dissolved oxygen is consumed, formation of acids
- non-LAB bacteria are suppressed by anaerobic conditions
- Complete lack of oxygen, high salt concentration, and low pH favor homofermentative LAB
- Optional storage
Sweet pickle production
after cucumbers have been washed, trimmed, submerged in a brine with started culture and fermented: the pickles are soaked in 25 to 30% sugar solution
Sausage fermentation
grind meat, add flavors and starter culture, blend, stuff into casing, incubate
Vinegar
sour wine, fermentation of alcohol to vinegar
Fermentation of cocoa
yeasts produce alcohols and aldehydes, ‘sweats’
- LAB produce lactic acid
- two main methods of fermentation: heaps of seeds and large boxes
morphology of Aspergillus
long strands/beans
Where is Aspergillus found in foods
grains, nuts, and spices
-molds are more dry tolerant
Geographical location of Aspergillus
more commonly found in subtropical and tropical climates
Aspergillus species that produces aflatoxin
Flavus and parasiticus
toxic effects of aflatoxin on human body
liver damage and cancer, kidney damage, immunosuppressive effect
mechanism of action of aflatoxin
Reactive intermediates bind to DNA and disrupts electron transport chain for ATP
How can aflatoxin be controlled?
UV light, ozone, hydrogen peroxide, anhydrous ammonia gas
Morphology of Penicillium
blue/green color, citrus fruits
-thread like extensions from a main base
Ochratoxin A
damages kidney
citrin
renal toxin
Patulin
no chronic effect
Cycloprazonic acid
liver and kidney damage
Citreoviridin
cereals
Fusarium
low toxicity, canoe shaped
Claviceps purpurea.
disease that develops from cereal grains, especially rye.
-Alkaloids like in LSD, hallucinogenic, may have been the cause of the Salem witch trials
two types of host specificity
humans only and zoonotic
life cycle of parasite
zygote (oocyst), sporozoite, merozoite, gametes
Cryptosporidiosis
Reservoir: humans, cattle, deer.
Transmission: Fecal oral route,
Foods: contaminated water
Signs and Symptoms: watery diarrhea, vomiting, stomach cramps
Epidemiology: 1-4 ages, affects mostly children because of swimming pools
Other: Chlorine resistant, prevalent in swimming pools, #1 waterborne disease
Cyclosporiasis
Reservoir: humans
Transmission: ingestion of oocysts my contaminated foods by handlers
Foods: raspberries and cilantro?
Signs and Symptoms: 1 week incubation, watery diarrhea
Epidemiology: tropical areas
Other: imported produce biggest source
Toxoplasmosis
Reservoir: cats
Transmission: ingestion of oocysts from cat poop
Foods: undercooked meats
Signs and Symptoms: asymptomatic
Epidemiology:
Other: schizophrenia linkage, can pass through placenta
Giardiasis
Reservoir: humans and animals Transmission: fecal oral route Foods: lake and streak water Signs and Symptoms: one or two weeks of watery diarrhea and stomach cramps and nausea Epidemiology: contaminated water Other: also known as beaver fever
Amoebic dysentery
Reservoir: humans
Transmission: fecal-oral route
Foods:
Signs and Symptoms: asymptomatic, 2-4 week incubation
Epidemiology: contamination from food handlers, irrigation water, etc.
Other: crowded areas with poor sanitation, bloody diarrhea
Trichinella
Roundworm (Nematoad)
Reservoir: animals
Transmission: eating raw or undercooked pork
Foods: pork
Signs and Symptoms: nausea etc. later on eye swelling, headaches
Epidemiology:
Other: pork
Ascaris
Roundworm (Nematoad) Reservoir: humans only Transmission: hands contaminated with eggs from dirt Foods: vegetables or fruit Signs and Symptoms: asymptomatic Epidemiology: Other:
Taenia
Tapeworm (cestodes)
Reservoir: humans
Transmission: raw or undercooked beef or pork contaminated with cysts
Foods:
Signs and Symptoms: asymptomatic
Epidemiology:
Other: more prevalent if under developed countries
Fasciola
Flukes (trematodes)
Reservoir: humans and animals especially sheep
Transmission: requires snails
Foods: watercress and freshwater plants
Signs and Symptoms: asymptomatic
Epidemiology:
Other: SNAILS ARE INTERMEDIATE HOST, live in liver ducts and eggs pass out with bile
