Environmental conditions that affectmicrobial growth on food.
What are some examples of extrinsic factors? (3)
What is "relative humidity"?
A measure of the water activity of the gasphase
How does food with low awstored at high humidity obtain water? What is the result of this?
The food absorbs water from the atmosphere. Condensation may occur on the surface.
What is the result of the condensation on the surface of foods?
The condensation provides ideal growing conditions for microorganisms.
Temperature has a major affect on ___________ ___________, __________________ and _______ ____________________.
microbial growth, physiology and gene expression.
Over what temperature range can microorganisms grow at atmospheric pressure?
What determines the micro-organisms range?
-8oC to 100oC
They range over which water is present in aliquid state.
What are the fundamental temperatures for growth? (3)
Growth rate decreases more_____________ above optimum than below optimum.
These organisms have an optimum growth rate at 10-15oC.
These organisms are able to tolerate lower temperatures but their ideal growth temperature is 20-30 oC -- they are quite common in our studies.
We are most familiar with these organisms. They have an optimum around 35-40oC.
Optimum growth rate at 55-60oC. We study these as well (spores).
These organisms are found under extreme conditions –these are a concern because they are not easily destroyed.
______________________ and ____________________ (two groups of organisms with specific growth temperatures) aremost important in food microbiology.
Mesophiles and pyschrotrophs
What are the effects of decreasing temperature? (2)
This increases the proportion of unsaturated and/or shorter chain fatty acids in cell membranes.
What is the result of increased proportion of unsaturated and/or shorter chain fatty acids in cell membranes?
This decreases the melting point, allowing membranes to remain fluid at lower temperatures.
_______________________ have higher levels of the fatty acids than mesophiles so their membranes remain fluid when the temperature is decreased.
What are the effects of increasing temperature?
Denaturation of proteins.
Thermal breakdown of cell membrane.
What will happen to the microorganism when the cell membrane begins to breakdown?
The organisms will die.
The _______ ___________________ is very importantas both we decrease and increase heat for organisms. Because of this, heat is a huge and familiartreatment that is used.
What are two gases in the atmosphere that can highly affect microorganisms?
O2 and CO2
What is O2 strongly involved in as far as its affects with micro-organisms?
_____ bridges both extrinsic andintrinsic factors which affect microorganisms.
_____ is inhibitoryto microbial growth. Why is this so?
As you lower the pH, CO2 willdissolve in water and become carbonic acid. Because acids can cross the memraben, the weak acid is able to penetrate the cell membrane andlower the intracellular (inside the cells) pH of the microorganisms.
_________ and ____________ ________ ___________ ________________ are most sensitive to the presence of CO2.
Fungi and oxidative gram positivebacteria
_______________ and some ____________ are mosttolerant to the presence of CO2.
What are two main dangers involved with the change of pH within the cells?
What affect does this have on the organism?
1. The pH change maychange physical properties of the cell membranes key enzymes.
2. The CO2 can react with protein amino groups changingtheir properties and activity.
This can have a deleteriousaffect on the organisms, as it tries to maintain its preferred state.
What are two examples of when we use CO2 to our advantage?
CO2 is usedin modified atmosphere packaging (ex. lots of the meats (preparedmeats) are packaged, sometimes vacuum packaged).
CO2is at elevated pressure in carbonatedbeverages.
CO2 is sometimes added to ______________ the growth of microorganisms.
Why is this packaging so important?
Once you are slicing things up,you are exposing all those lovely nutrients to the environment where therecould be microorganisms. We package the food in a way to try to inhibit the growth of these orgnaisms.
Implicit Factors (4)
Properties of the organisms themselves which will limit growth.
How the organisms respond to their environment.
How the microorganisms interact with one another.
Physiological state of the organism.
(These factors will affect how an organism will grow and flourish).
What are two intrinsic factors that really distinguish the fate of microorganisms?
Specific growth rate.
Ks (affinity for substrate).
High affinity for a substrate means a _______ Ks value.
If two microorganisms land on the same food, which is more likely to survive?
The one with the higher growth rate as well as the organism with the higher affinity for the substrate (low Ks).
Organisms with a higher ________ _____________ will usually predominate when competing for growth on food.
When is a low Ks value particularly crucial for the survival of a microorganism?
If we’re looking at relatively low concentrations of nutrients.
Cells growing ______________________ are moresensitive to stresses than those in stationary phase.
Pre-adaptation to stress will enhancesurvival.
What are three key examples of this?
Growth at higher temperature willincrease resistance to heat.
Exposure to moderately lower pH willenhance resistance to more severe pH decreases.
Growth at successively lower temperaturescan reduce the minimum temperature for growth.
What are two of the mechanisms that microorganisms use to enhance resistance to stresses?
Production of heat shock proteins.
Stationary phase sigma factor RpoS.
How are heat shock proteins produced in microorganisms? (2)
The proteins are coded for by genes which have Sigma factor, RpoH for transcription.
Chaperones interact with proteins andassist in proper conformation.
What is the stationary phase sigma factor RpoS?
(where is it found, what is it's mechanism of action)
The sigma factor is a general stress response regulator found in Gram negative bacteria.
Directs the transcription of many genesin stationary phase, some of which are protective – this leads to cross protection
The stationer sigma factor RpoS confers resistance to many stresses including _____ ______ and ___________.
Sigma factor RpoS also regulates expression of genes involved in what?
Sigma factor RpoS also regulates expression of genes involved in virulence in some food-borne pathogens.
What are the two types of microbial interactions?
What are two examples of this type of relationship?
When the growth of one organism stimulates thegrowth of another.
Example 1: yogurt starter cultures.
Example 2: one organism degrades a complexfood component into smaller more readily assimilatablecomponents which can be used by another.
How do some microorganisms cause this relationship? (2)
When one organism inhibits the growth ofanother.
Some microorganisms hide/isolate essential nutrients such as iron. Other organisms do so by producing inhibitory compounds.
How do Lactic Acid Bacteria create antagonistic relationships? (2)
They produce lactic and acetic acids whichlower pH and inhibitmicrobial growth.
Lactic acid bacteria also produce bacteriocinswhich inhibit bacterial growth
How can we best predict food spoilage, shelf life and food safety?
We can do so by understanding of intrinsic, extrinsic and implicit factors that affect microbial growth and their effects on the survival of food.
How did we first begin to make predictions about the effects of these various factors on microbial growth and survival?
What was a disadvantage of this means of study?
Earlier studies focused on the effects ofone or two factors on microbial growth and survival while all others were kept optimal.
This may not be realistic in many foods wheremicroorganisms may encounter a host of factors at suboptimal conditions forgrowth.
What is an advantage of the way in which we first begin to make predictions about the effects of these various factors on microbial growth and survival?
It may have been possible to use this information to enhance food stability and safety.
Introduced the "Hurdle Concept" in 1978.
This explained the application of combined preservative factors (hurdles) to reduce microbial growth and survival and enhance food stability and safety.
This idea had been known inherentlybefore in that when people were preserving foodthey might heat it, add salt, etc. But this was done withoutreally understanding what theimpact might be on the microorganisms. By using the information that we havenow, of the effect on the individual organisms, we can predict what the best way for food preservation will be.
By enhancing and inforcingmulitplehurdles, you will eventually ________ the growth of the organism.
What is the simplistic idea behind the hurdle concept?
If you combine a number of hurdles (preservative methods), you can knock the organisms out.
This approach is becoming more and more common.
What advantages did the Hurdle Concept bring about? (3)
This caused people to appreciate the importance in the desire to improve food quality as well as safety
The hurdles also us to decrease the negative effects of harsh preservatives (which can really affect the taste/texture of the food) because it may be possible to lower dosage of individual factors/hurdles. This allows food to stay in it's most natural state.
What are three ways in which the hurdle concept affects microorganisms?
Homeostasis is maintenance of a stablestate within the cell (for example, the pH).
What will be the affect of the disruption of microbial homeostasis temporarily or permanentlyby hurdle factors? (2)
This disruption of homeostasis will increase the lag phase and inhibit growth (this prevents the organism frommoving into the exponential phase).
How do we disrupt the homeostasis of microorganisms?
This disruption occurs when adding multiplestresses because it might turn on shock proteins as well as the proteins involved with maintaining ion flow.
What is the affect of turning on these genes which are not usually transcribed and translated?
Expressing new genes and manufacturing them may require ATP – this takes energy from the cell. By applying a series of small amounts of hurdles or factors will strain the ability of the organism to cope. This will turn on all of these different genes that are now expressed, using up a lot of energy. Less energy will be availableto support growth of the organism.
So we understand that shock proteins can help to protect micro-organisms from stress. When under multiple stresses then, why is turning the shock proteins on not helpful?
We did talk about how thesynthesis of shock proteins which can enhance survival. This is true if you’relooking at one stress but if you’re applying multiple stresses, there just maynot be the energy to produce a sufficient quantity because there will not be sufficient energy for the microorganism to support other essential functions to survive.
How do hurdles cause metabolic exhaustion in microorganisms?
The application of sub-lethal hurdles strainsmicrobial repair mechanisms, which uses available energy and may lead to cell death.
How do hurdles cause stress reactions in microorganisms?
The synthesis of stress shock proteins maybe induced which could enhance survival, but may be less effective undermultiple stresses applied at once and their synthesis may consume more energyleading to metabolic exhaustion and death.
What are two approaches we can use to precithow long we can store food for?
First you inoculate the food spoilage or pathogenonto food. The food is then put in presence of simulated storageconditions and/or hurdles.
What are two disadvantages of challenge trials?
Expensive and time consuming, limited predictive value.
Data apply only to the exact conditions used in the trial (so when you're trying to look at how to manage risk, this is not very useful).
What are few mathematical models we use in predicting the spoilage of foods? (3)
Response surface models.
What's an example of this model?
Quantitative assessment that an eventwill occur.
Example: The probabilityof toxin production by Clostridium botulinumand the level of factors present – aregression equation.
Response Surface Models
What is an example of this model?
Provide information about the rate of change, timed to an event.
Example: The combinedeffect of pH and temperature on growth on time for a 2 log10 increase in Yersinia.
What was Gupta's study using the response surface model?
Citric acid treatment in combination withgamma radiation and modified atmosphere packaging was employed as hurdles forcontrol of microorganisms and extending shelf life of minimally processedFrench beans.
Response surface methodology was used tooptimize citric acid treatment and γ-irradiation dose to obtain product withdesired microbial and sensory quality.
What was the result of Gupta's experiment?
The experiment showed the ideal conditions for a product over one week in shelf life withacceptable sensory and nutritional quality as evaluated by total antioxidant, phenolics,flavonoids and vitamin C content.
In simple terms, what is Gupta's experiment showing us?
They use computer software todetermine the affect of three different variablesat one time to improve the stability of the food product over a week.
Take into account how fast amicroorganism will grow, its lag phase and model these as the response variablefor different factors such as temperature, pH and aw.
Mathematical models predict the effect of factors on howmicrobial numbers ______________ over time.
Several types of mathematical models have been developed. What is the Sigmoidal/Gompertz/ Baranyimodel good at representing?
The model is a 3D representation of how a micoorganism will change with a fixed factor (such as pH) over time.
Square Root Model
A linear relationship between temperatureand square root of growth rate.
(This model is of limited value when a variety ofparameters are used).
These models are becoming increasinglysophisticated with ________________ ________________ __________________.
computer software applications
When are mathematical models used?
Give an example of this.
They're usedto predict real world situations
Example: What is the effect of fluctuating temperaturesduring the distribution chain of a product from factory to consume?
Lappe published a paper concerning an increase of human salmonellosis due tothe serotype __________________ which hasbeen observedthroughout the world, mainly related to chicken eggs and derivatives.
______________ ______ is a bacteriocinisolated from Bacillus cereus.
What affect did cerein 8A have on SalmonellaEnteritidis?
Cerein 8A caused a significant growthinhibition of SalmonellaEnteritidis,suggesting a bactericidal mode of action.
A metal containing agent that disrupts the permeability barrier of the outer membrane.
Lappe et al. discovered that cerein 8Awas effective with relatively ____________ doses of EDTA or sodium lactate.
A weak organic acid involved in good microbiology.
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