Spoilage Flashcards
- What are the six causes of spoilage?
Microbial
Mechanical
Insect damage
Chemical and enzymatic
Physical
Physiology of the product
What is the difference between a spoiled product and actual spoilage?
Spoiled product: quality perceived unacceptable
Spoilage: process of decreasing quality
What does the shelf life depend on (microbiologically)?
Initial contamination of the food and growth rate of microorganisms
What are some examples of primary contamination? (give two)
Animals/plants (raw materials)
What are some examples of secondary contamination? (give three)
Water
Equipment
Air
People
Vermin
What are the four phases of microbial growth?
Lag phase
Exponential phase
Stationary phase
Death phase
What are the two main shapes of bacteria?
Cocci and rods
What is the average size of yeasts & molds?
10 micrometers
What mechanism do yeasts use to grow?
Budding
Do viruses grow on food?
No
Are viruses important in the appearance of foodborne illnesses? Why?
Yes because they can produce mycotoxins
Give an example of a parasite
Ticks
What are the environmental factors that influence the viability of a microorganism?
Suitable ecological niche and competitive advantage
In which phase of the growth curve are bacteria adapted to the environment?
Exponential phase
What is growth kinetics?
Study of increase of cell numbers in time
What are 2 ways to increase the shelf life of a product in terms of growth kinetics?
Reducing the initial contamination or increasing the generation time
What is the difference between intrinsic and extrinsic factors
Intrinsic factors are properties of the food itself and extrinsic is properties of the environment the food is in
How are m.o in food classified? (e.g. photo lithotroph)
Mostly chemo heterotrophs
What is an example of a physical nutrient barrier?
Shell of nuts, peels
What is the aim of antimicrobial barriers?
Hinder growth through lack of access to water and nutrients, leave microorganisms without environment protection
What do the following four enzymes degrade?: Pectolytic, amylytic, lipolytic, proteolytic
Pectolytic: pectin
Amylytic: Starch
Lipolytic: lipids
Proteolytic: proteins
How does preservation work?
By changing product formulation (increasing/decreasing nutrients) or processing (introducing/removing barriers)
What are the pH optimums for foodborne bacteria, yeast and mold?
Bacteria: around 7
Yeast: around 4.5
Mold: around 3.5
Which kind of acids (dissociated or undissociated) can easily pass through membranes? How do they do this?
Undissociated acids through proton motive force
How is pH applied in preservation?
Fermentation: Lactic acid bacteria lowers pH and inhibits growth of pathogens
Acid preservatives
How do yeasts and molds make the environment more suitable for pathogens?
They dissimilate the acid and alter the pH
How do aerobic organisms get oxygen?
Oxidative phosphorylation with oxygen as electron acceptor
What is a facultative anaerobe?
Does not require oxygen but grows better with oxygen
What are ways to change the redox potential of a product?
Milling/grinding and lowering to increase Eh microbial growth lowers Eh
What m.o are more sensitive to CO2?
Molds, oxidative gram negative bacteria
What m.o are more resistant to CO2?
Gram positive bacteria and yeasts
What is water activity?
Measure of free water in food
What is the aw min of xerophilic and osmophilic m.o?
Xerophilic: 0.6
Osmophilic: 0.62
What are 3 ways to lower the aw of the product?
Adding solutes
Removing water
Combined application
What are 3 natural preservatives in milk?
Lysozyme
Lactoferrin
Antibodies
What are 3 natural preservatives in eggs?
Lysozyme
Avidine
Conalbumine
What m.o are inhibited by the addition of acids?
Lactic acid inhibits gram negatives and listeria
Yeasts, molds and lactic acid bacteria by the rest
What do SO2 and nitrate do to help preserve a product?
Disrupt microbial metabolism
What is important to keep in mind when using freezing to preserve a product?
Physchrophiles and psychrotolerant m.o can still grow, freezing stops growth but allows survival
When does the growth rate stop increasing?
When the optimal temperature is reached
What are implicit factors?
Properties of m.o themselves and interactions between them
What is the most important implicit property that influences spoilage?
Specific growth rate during optimal conditions
Which are killed more easily? Cells in exponential/stationary phase?
Exponential phase
What environmental stresses can affect the physiological state of a microorganism?
Injury due to freezing or dissecation
What are the 5 most important interactions between microorganisms?
Competition
Obligate symbiosis
Mutualism
Commensalism
Antagonism
What is the difference between symbiosis, commensalism and mutualism?
Symbiosis is obligate (both microorganisms need it), mutualism both benefit from each other, commensalism is only one benefits from the other one
What is amensalism?
One microorgannism generates harmful compounds for another one
What is the Hurdle effect?
Combination of sub optimal factors that preserves the product sufficiently
What are the 4 options to evaluate spoilage or health risks?
Ask an expert
Challenge test
Storage test
Predictive microbiology
What are the pros and cons of asking an expert?
Pros: quick, proposal told if good or bad idea
Cons: Not quantitative
What are the pros and cons of a challenge test?
Pro: representative for the product and organism
Con: Time consuming, expensive, only representative of the conditions set
What are primary growth models?
Describe contamination levels in time described by the specific growth rate
What are secondary growth models?
Describe the influence of intrinsic and extrinsic factors of the food on the growth rate
What is gamma modeling?
Combination of primary and secondary modeling
What three factors do food manufacturers have to balance out?
Food quality, shelf life and costs
What three effects does processing want to have on microorganisms?
Keep microorganisms out
Kill microorganisms
Keep microorganisms from growing
What main 4 methods are used to kill microorganisms?
Radiation
High pressure
Pulsed electric fields
Heat inactivation
Which of the radiation rays are more effective in killing microorganisms and why?
Gamma rays because they have deep penetration
What are the advantages and disadvantages of using high pressures to kill microorganisms?
Pros: instant and uniform, low effect on the quality
Cons: some enzymes are difficult to inactivate, difficult to scale up
What survives after pasteurization?
Some pathogens and sporeformers
What survives after appertization?
(sterilization): non pathogenic survivors that can’t develop in the product
What is blanching used for?
Decontamination and enzyme inactivation
What does the Sous vide environment consist of?
Vacuum product with heat treatment and refrigeration
What is the unit of D value?
Time
True or false: D value goes up as the temperature goes up
False d value goes down
What is a D value?
Time required to reduce cell number by 1 log
What factors influence the increase the D value? (name two)
pH, aW, temperature, food matrix
What is the Z value?
Change in temperature that yields a 1 log change in the D value
What is the unit of Z value?
Temperature
What is the Z value of vegetative cells?
5 degrees
What is the Z value of spores?
10 degrees
What is bigger? D/Z value of spores or vegetative cells?
D and Z value of spores is bigger than in vegetative cells
What is the F value?
Integrated lethal effect
What is the Lethal rate?
Relative inactivation rate at a certain temperature
What are the 3 main sources of contamination of raw milk?
Dirt on exterior of teats
Interior of teats
Milking equipment
What are the 4 ways of contamination of teats?
Feed, feces, bedding and soil
Which microorganisms naturally occur in soil that can contaminate cows?
Spores (bacillus) and Listeria monocytogenes
Which microorganisms naturally occur in feces that can contaminate cows?
Campylobacter, Salmonella, E. coli
What is mastitis?
Inflammatory disease in mammary tissue
What are preventive measures for milk contamination?
Don’t feed moldy silage
Clean teats and equipment
Milk quality payment system
What are the main curative measures for milk spoilage?
Kill microorganisms with heat (Pasteurization and sterilization)
Remove microorganisms (Bactofugation and microfiltration)
Prevent microorganisms from growing with low temperature, Aw and pH
Which microorganisms survive pasteurization?
Bacillus cereus
Lactobacillus
Microbacterium
Which microorganisms survive UHT?
Bacillus and other sporeformers
Which microorganisms can grow post pasteurization?
Pseudomonas, alcaligenes, Acinetobacter, psychrobacter
Why do microorganisms still grow in milk even if its chilled?
Because milk is still a good medium for growth (good nutrients)
What is spoilage association determined by?
Raw material flora
Processing
Storage conditions
Preservation
What happens to the pH of the meat after the animal dies? Why?
It drops from neutral to 5.5 because lactic acid is produced due to gycolysis
Where in the animal can you find spoilage associated microflora? Where can you find safety associated microflora?
Spoilage: hide, skin, hair and feathers
Safety: gastro intestinal tract
Where in the animal is relatively free of microorganisms?
Internal organs and muscles
About how many microorganisms does a primal cut of meat have?
10^2-10^4
In what temperature is meat normally stored at? Which flora can grow? Name two examples
Low temperatures, psycho-tolerant flora such as Pseudomonas, Enterobacteriaceae and Lactic Acid Bacteria can grown
What 4 preservative factors can be used to conserve meat?
Exclude oxygen
Increase CO2
Freezing
Heat treatment
What are the advantages and disadvantages of MAP?
Maintains red color of meat
Spoilage flora depends on temperature of storage
What are the advantages and disadvantages of freezing?
No microbial growth under -18C
Growth after defrosting, enzymes of killed microorganisms can still act
What heat treatments can be used on meat?
Pasteurization and sterilization
What 2 components help preserve cured meat?
Salt and nitrite
What issues can arise with cutting of deli meat?
Souring and discoloration in package
Contamination with psychrotolerant bacteria
Why does fish have such a short shelf life?
Because the death struggle consumes all sugars and there is no post mortem acidification
Why do cut vegetables have a shorter shelf life than their uncut counterparts? Name 4 factors that influence this.
Nutrients available
Aw is higher
More oxygen interacting
Contamination spreads
