Microbial spoilage Flashcards
(94 cards)
1
Q
Why it is necessary to understand microbial food spoilage mechanism?
A
- A spoiled food isn’t necessarily unsafe
- Spoiled food is mostly an economic issue, but it’s also a food security issue
- Therefore, understanding the causes and mechanisms of microbial spoilage is important in order to minimize the losses and provide a high-quality food supply with adequate shelf life
2
Q
What is common and different between meat, poultry, and seafood?
A
- These products are all similar in that they are “muscle foods”
- They are rich in nutrients (aka bacterial substrates), which allows extensive microbial growth and support the growth of bacterial pathogens and high in moisture
- They differ in that they have different ”original” microbiotas, leading to a different succession of microbial spoilage bacteria
- They differ in the handling and storage requirements, which also leads to a different microbial succession
3
Q
Is meat free from bacteria when alive? when it can be acquired? Sources
A
4
Q
What is the first event in microbial meat contamination and who is good at it?
A
5
Q
, the best way to preserve meat is …
A
- In general, the best way to preserve meat is to have a very clean processing facility so that minimal numbers of bacteria attach to the surface of the meat
- Animal carcasses must also be washed with potable water immediately after slaughter in North America
6
Q
What is the measure threat for food processing environments?
A
Biofilms
- They can form on almost any surface (stainless steel, aluminum, nylon, Teflon, rubber, plastic, gaskets etc.) and can persist despite extensive cleaning efforts for years!?!
- Mono- or multispecies bacteria can be formed by spoilage or pathogenic bacteria
- Once formed bacteria in biofilms can be 10- to 100-fold more resistant to sanitizers in comparison to planktonic cells
7
Q
What bacteria is very good at colonizing stainless steel?
A
Lysteria monocytogenes
8
Q
How much of meat and fish is wasted at all stages and why it is a problem
A
•One-fourth of all meat, and 30% of all fish are lost due to microbial spoilage!!!
Terrible-> people could have eaten
2-> Carbon emissions
3-> animal welfare
9
Q
What affects microbial succession patterns and general rules?
A
- Conditions of the slaughter, decontamination, and storage will affect the microbial succession
- But in general aerobic Gram-negative bacteria mostly Enterobacteriaceae will dominate the microflora under cold aerobic conditions, and LAB will dominate vacuum-packaged products
10
Q
How microbial interaction play a role in microbial succession and give a concrete example
A
- Microbial interactions also play a role, microbes compete for nutrients, produce favorable or unfavorable environments for each other, and quorum sensing and this can also affect microbial succession
- Pseudomonas inhibits Shewanella and promotes Listeria
- Pseudomonas utilizes glucose and produces siderophores at higher rates than Shewanella
- Pseudomonas also hydrolyses proteins and provides amino acids to Listeria
11
Q
Why spoilage is not a set term?
A
- Spoilage is defined by consumers rejecting a food based on undesirable sensory characteristics
- Based on the definition of spoilage it is at the discretion of the consumer (subjective), and will differ based on socio-economic factors
12
Q
What will be the difference in proteolytic, non-proteolytic and canned food spoilage
A
- Microbial spoilage can lead to off-flavors, off-odors, off-textures, discoloration, and slime
- Proteolytic spoilage results in putrid odors due to breakdown of amino acids
- Non-proteolytic spoilage results in sour odors
- Spoilage of canned foods is usually due to improper process control, and results in the proliferation on mesophilic spore formers
13
Q
What are the substrates, chemical changes, and spoilage happening in meat (both aerobic and anaerobic)
A
14
Q
why lobsters, carbs, and crayfish are kept alive until cooking
A
•Crustaceans are an exception to the rules above because endogenous tissue enzymes in their hepatopancreas cause rapid postmortem muscle breakdown, this is independent of microbial proteases
15
Q
What is the ideal spoilage indicator should have
A
- Be absent or present in very low levels in fresh tissue
- Be produced by the spoilage microflora
- Increase with storage time
- Correlate well with sensory analysis
16
Q
Is it easy to evaluate the spoilage of the meat?
A
- The definition of Spoiled will depend on the food, preservation interventions, geography, so its hard to come up with a really good way to evaluate freshness
- Sensory evaluation is probably the best way to evaluate freshness of spoiled meat, but this requires trained experts for regulatory purposes and is very subjective
- Microbiological analysis is also available, but its very general and can be a destructive process
- Efforts have been made to develop quantitative biochemical changes to define spoilage level (production of amines, ammonia, trimethylamine, and sulfur)
17
Q
What is traceability?
A
•Traceability is the ability to maintain credible custody of the identification of animals and their products from production to retail
18
Q
Why traceability is important?
A
19
Q
•The strategy for microbial control in meats is generally focused on good hygiene and proper storage and includes:
A
- Select
- Reduce
- Decontaminate
- Process
- No cross-contamination
- Low T storage
- Harvest, or ship animals for slaughter with low contamination
- Reduce the potential for transfer of microorganisms to carcasses, meat, and seafood from water and the environment
- Apply safe and effective decontamination interventions
- Apply processes (heat, high pressure, irradiation) to reduce or eliminate microorganisms
- Avoid cross contamination at all stages6.Store products at low temperature, using packing conditions that discourage bacterial growth (we will talk more about storage later on)
20
Q
Common microbes on fresh red meat are ___
Present in lower populations ___
A
•Gram-negative rods and micrococci (Pseudomonas, Enterobacteriaceae, Acinetobacter, Staphylococcus, Micrococcus, coryneforms, and fecal streptococci)
LAB, Bacillus, and Clostridium spores
21
Q
What is the range of microbes on meats?
A
•Initial contamination levels vary from 102-107 CFU/cm2of aerobic mesophiles
22
Q
___ are the dominating spoilage microorganisms in red meat at cold temperatures, on aerobically stored meat
A
•Pseudomonas spp.
23
Q
What is dominant bacteria whem the meat is immediately vacuum packed?
A
Gram-positive bacteria
24
Q
Why stressed animal’s meat will become spoiled more quickly?
A
Remember microbes like to use glucose before amino acids for energy production, and amino acid degradation leads to more signs of spoilage
•If the animal was stressed or exercised before slaughter it will lead to decreased levels of glucose in the tissue, this leads to faster degradation of the amino acids and detection of spoilage at lower bacterial cell densities (106CFU)
25
How microflora and spoilage is different in stakes vs ground beef?
* Intact meats (steak) spoil more slowly than comminuted meats (ground beef) because of higher levels of initial contamination, larger surface area, cross contamination during grinding, the release of fluids for bacterial growth media due to cells rupturing during grinding
* In ground meat the dominant microflora on the exterior are similar to steak (*Pseudomonas*) but LAB may dominate the interior due to oxygen limitation
26
How processed meats degradation is different from fresh?
27
The greening of the surface for processed meats is due to what type of bacteria?
•Greening is due to the production of hydrogen peroxide by ***Lactobacillus viridescens*****,*****Streptococcus*****, or** ***Leuconostoc***
28
Slime in processed meats is due to what bacteria?
•Slime is usually confined to the surface and is associated with the growth of yeasts, ***Lactobacillus*****,*****Enterococcus*****, and** ***B. thermosphacta***
29
What spoils dry-cured meats?
•Dry-cured meats mostly spoil because of yeasts or molds that tolerate extremely low water content
30
How much poultry is consumed globally?
•Approximately 31% of meat consumed globally is poultry, most of this is chicken
31
Where chicken get its bacteria? and how much
* Most of the microbiota associated with poultry is acquired from the bird’s skin and feathers, with some acquired during processing
* At the end of processing most poultry products have a bacterial population ranging from 101-104 CFU/cm2
* Each step in the processing of raw poultry will affect the level and type of spoilage bacteria, with some steps leading to an increase in population and some steps leading to a decrease
32
Specific types of bacteria that are found on poultry
* Bacterial populations associated with the carcass at the end of processing have predominantly Gram-negative bacteria (*Acientobacter/ Morazella*, *Enterobacteriaceae*, and *Pseudomonas* spp.)
* During refrigeration storage the *Pseudomonas* spp. group becomes predominant
33
What is the processing poultry from live chicken to end product? what are the specifics of each step?
34
What is the last step of poultry processing after evisceration? How it can be achieved? what is lost during this period, do not forget about bacteria
35
What substrate is first used when chicken is spoiled And then what? the most common spoilage organism at refrigeration temperature?
* Again, the spoilage bacteria metabolize glucose first, which leads to a population of 108 CFU/cm2
* After glucose is used, the bacteria metabolize amino acids which leads to the production of off-odors
* The most common spoilage organism at refrigeration temperatures is *Pseudomonas* spp. but yeasts can also be involved in spoilage
36
Several foodborne pathogens are associated with seafood including
•*Salmonella, Clostridium botulinum, Aeromonas, S. aureus, L. monocytogenes, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus*
37
Where most fish is coming from nowadays and what is the implication?
•For several years wild fisheries supplied the world with fish, now aquaculture has outpaced wild fisheries, therefore the species variety is more limited
The crowding and stress found in aquaculture systems enhance the spread and growth of bacteria (especially pathogens) so aquacultured fish tend to have a higher bacterial load than their wild counterparts
38
What is biogenic amines?
•Biogenic diamines including: **histamine*****,*** cadaverine, and putrescine can be produced postmortem by fish or shellfish tissue
39
Can a properly cooked fish result in food poisoning?
•**Histamine is not destroyed by cooking, so even properly cooked spoiled fish can result in poisoning**
40
What can cause scombroid food poisonings?
Consuming biogenic amines
41
Why there is an additional concern about biogenic amines and cold-snoked fish?
•An additional concern is that if nitrite is used in cold-smoked fish products that are not fresh enough, putrescine and cadaverine will react with that nitrite to produce carcinogens.
42
How biogenic amines are generated in fish?
* These diamines are produced by the **decarboxylation** of specific free amino acids
* Decarboxylation generally occurs via the release of decarboxylase from the various microorganisms growing on the food product
* Fish muscle is naturally rich in free amino acids, and this increases even more after the fish dies
* For example, histidine is an amino acid that exists naturally in several food products. At temperatures above 16C, histidine is converted to **histamine** via the histidine decarboxylase enzyme that is produced by *Morganella morganii* which is a symbiotic bacteria in fish.
43
Symptoms of scombroid food poisoning, how fast is onset?
* Symptoms include flushed skin, headache, itchiness, blurred vision, abdominal cramps, and diarrhea
* It onsets 10-60 minutes after eating and can last for two days
44
Why scombroid food poisoning develops in fish? What does it reassemble? what drugs can be taken
* It results if the fish has had inappropriate storage, resulting in microbial growth, resulting in production of biogenic amines, such as histamine
* Histamine is the main natural chemical responsible for true allergic reactions, so the symptoms are almost identical to a food allergy
* Anti-histamines can be taken to alleviate symptoms of scombroid food poisoning
45
What is the most exportable seafood product in the world?
•Shrimp are the most exportable seafood product in the world. Globally, 75% of shrimp production occurs in developing countries, while 75% of shrimp consumption occurs in developed countries.
46
What microbiological concerns are there for shrimps?
* **Pathogenic vibrios** are routinely present in the water where shrimp are raised, pathogenic vibrios occur in these waters regardless of if there is fecal contamination or not, and can attach to and colonize the exoskeletons of shrimp
* Fecal contamination of growing ponds is not uncommon and coliforms and ***Salmonella*** are common in shrimp rearing environments
* The organisms responsible for refrigerated shrimp spoilage are mainly ***Pseudomonas*** **and** ***Aeromonas***
47
What foodborne pathogens are found in shellfish?
•Vibrios (both pathogenic and non-pathogenic) are found as native organisms in the estuarine environments where bivalves are collected and farmed
48
Oysters and mussels: precaution
* Oysters are filter feeders that can concentrate the native water microbiome, and since oysters are often consumed raw they are associated with several outbreaks
* Mussels also concentrate bacteria and are not recommended to be eaten raw
49
Why milk is pasteurized (being afraid of what microorganisms)? and why else
Lysteria and e.coli
and to increase shelf life
50
Why milk is a great medium for growth of some microorganisms but for other not
* Milk is a great growth media for bacteria because of its **high water content, near-neutral pH, and available nutrients**
* It does not support all microorganisms because it has low amounts of available amino acids
Several milk spoilage bacteria can rely on **proteolysis** or **lipolysis** for energy generation
51
Proteolysis and lipolysis happen at different temperatures: at what temp each occurs faster
* Milk lipolysis actually happens faster at 4C than at 7C because during cold storage psychotropic bacteria have a faster growth rate and produce more lipases
* Proteolysis, on the other hand, occurs more quickly at 7C than at 4C
52
Psychotropic bacteria: what flavor defect they will do, types of enzyme, metabolic products
53
What diffect LAB can bring to milk, types of enzymes and metabolic products
54
When milk curdles: what bacteria is responsible for it? what enzyme, metabolic products, what it can say about refrigerator
Refrigerator is not functioning properly, temp is too high (7C)
55
How available carbon is for bacteria in milk
56
How available nitrogen is in milk
57
What are two major natural inhibitors of microbial growth in milk
Lactoferrin and lactoperoxidase
58
What lactoferrin does
•Lactoferrin binds iron, making iron a limiting factor for bacterial growth in milk.
Lactoferrin is of great importance in limiting bacterial growth in human milk, which is low in citrate.
However, there is more citrate cow’s milk. Citrate binds iron, which limits the ability of the lactoferrin to limit bacterial growth
59
What does lactoperoxidase, what conditions it survives
•The lactoperoxidase system is the most effective microbial inhibitor in cow’s milk.
**Lactoperoxidase survives pasteurization**.
It catalyzes the oxidation of **thiocyanate** (*when hydrogen peroxide is present*) and in the process creates **hypothiocyanite**, which is a highly reactive oxidant, and is antimicrobial
60
What are natural inhibitors of lesser importance
Natural inhibitors of lesser importance are **lysozyme**, specific immunoglobulins, and folate and vitamin B12 binding systems
61
Coming back to hydrogen peroxide and lactoperoxidase…
What is the limiting factor in lactoperoxidase system, what can be done to improve effectiveness? How is it employed in developing countries
* **Hydrogen peroxide** is the limiting substrate in the lactoperoxidase system
* Therefore, adding a hydrogen peroxide generating system to the milk will increase the effectiveness of the lactoperoxidase system
* Therefore, in developing countries this system is used, by adding additional hydrogen peroxide to extend the shelf life of raw-milk especially when there is a lack of refrigeration facilities during on-farm storage
62
What type of bacteria are susceptible to lactoperoxidase system
•LABs, coliforms, and several pathogenic bacteria are limited by the lactoperoxidase system - provided that there is enough hydrogen peroxide present
63
What is the shelf life of pasteurized milk? How it can be extended or shortened?
* The shelf life of pasteurized milk is supposed to be **16-22 days**
* Natrel markets fine **filtered milk**, where milk is passed through a filter after pasteurization to remove any surviving bacteria. They claim that the milk stays fresh for **37 days**, in a sealed package.
* Growth of psychrotrophic bacteria in raw milk can also lead to product defects because of **residual activity of heat-stable enzymes**
64
What is done to milk before pasteurization? Why? what if fails to do it
* Preservation of milk relies on effective sanitation (pasteurization) and refrigeration
* Raw milk is kept cold until pasteurization after which it is kept cold again until consumption
* There is often time between collection and consumption for psychrotrophic bacteria to grow and flavor defects result from this growth
S.aureus causes mastitis in cow's, and it produces toxins that are heat stable, so you need to keep the milk refrigerated before pasteurization
65
What is the predominant type of bacteria that will spoil both raw and pasteurized milk?
•**Psychrotrophic** bacteria that spoil both raw and pasteurized milk are generally **aerobic Gram-negative rods**
66
what bacteria is the most prevalent in raw milk? what other bacteria are present? what happens to bacterial population during storage and the type of bacteria (aerobe, anaerobe, etc.) in spoiled refrigerated milk
* 65-70% bacteria isolated from raw milk will be ***Pseudomonas sp**.*
* ***Aeromonas*****,*****Bacillus*****,** ***Listeria*****,*****Staphylococcus*****, and** ***Enterococcus*** will also be present
* Obligate aerobes will usually be the most populace microbes in spoiled refrigerated milk
* ***Enterobacteriacea*** increase in numbers during milk storage, but eventually they will be over grown by ***Pseudomadaceae***
67
what exception is there for the succession of Enterobacteriaceae by pseudomaceae
* Though an exception to this is when bacterial spores are also present in the milk
* The majority of aerobic spores found in milk usually belong to the genus *Bacillus*
68
What process (proteolysis or lipolysis) is mostly responsible for milk spoilage in the fridge?
•Psychrotrophic milk spoilage usually relies on proteolysis to spoil the milk, and to a lesser extent lipolysis
69
What process Pseudomonas sp. is unable to do in milk
•**The bacteria most associated with milk spoilage,** ***Pseudomonas sp.,*** **are unable to ferment lactose**
70
How raw milk and pasteurized milk can be contaminated
* Raw milk can be contaminated by psychrotrophic bacteria by almost any source present on the farm
* Pasteurized milk becomes contaminated by psychrotrophic bacteria in the milk processing plant equipment and air
* A study showed that the bag/ carton filling equipment was most often the source of spoilage bacteria in packaged milk
71
What in the life of bacteria makes milk to spoil? in what ways
* Defects in spoiled milk are generally the effect of extracellular enzymes
* **Bitter and putrid flavors** and coagulation result from **proteolysis**
* **Rancid and fruit flavors** are the result of **lipolysis**
72
Why there is a difference between spoiled yogurt and milk left on the counter when in both it is LAB acting
* Spoilage of milk by LAB can occur when the milk is temperature abused, and is stored at **temperatures** sufficiently **high** for **Gram-positive** acid-producers to outgrow psychrotrophic bacteria
* Although desirable fermented milk products can be produced, milk can be spoiled by “**wild” LAB that produce unwanted gas**, or **off flavors** (remember dairy products almost always use starter cultures)
* Lactic acid by itself tastes good, but **“wild” LAB** produce **acetic acid and propionic acids** that produce off tastes
73
Why different dairy products spoil differently
Depending on water activity, pH and water content
In butter→ low butter high pH→ mostly mold
in yogurt high water→ bacteria
74
Why there is no one scheme that fits all for fruits and vegetable spoilage?
* Making generalizations about the spoilage of fruits and vegetables is difficult because a single produce item such as a tomato could be cultivated under several different conditions under many different climates
* Each variable will affect the bacterial load and how the tomato spoils
* There are also a huge variety of produce products globally
75
What bacterial population range is there for F&V and for yeast and molds?
* The bacterial aerobic mesophile population on fruits and vegetables can range from **102-108 CFU/g**
* The yeast and mold populations range **101-107 CFU/g**
76
What is the characteristic that negatively associates with shelf life and how it measured
* Once detached from the plant, the respiration rate of fruits and vegetables correlates negatively with shelf-life
* Respiration is measured in CO2/kg/hr at 5C
77
Products with high and low respiration rates
* Products with a **low respiration rate** (apples, potatoes, onions, garlic, carrot, or cantaloupe) can be stored for a long time
* Products with a **high respiration rate** (strawberry, raspberry, spinach, asparagus, or mushrooms) have a short shelf life
78
what gas increases produce maturity?
Ethylene
79
Respiration leads to ___ loss leading to structural damage as \_\_\_
•Respiration also leads to moisture loss leading to structural damage (apples) and wilting (leafy greens)
80
How fruits and vegetables get contaminated
•Fruits and vegetables are usually contaminated from the environmental sources that they were grown in
81
If fruits and vegetables are naturally covered with microorganisms why not every fruit spoils fast?
* Spoilage, to some extent is caused by the **penetration of microbial cells** into the plant tissue
* The **cuticle barrier** can be **compromised** by several spoilage bacteria by various enzymatic processes
* Spoilage fungi can form a **appressorium** at the end of their germ tubes. This structure is used to attach to and then penetrate plant surfaces by mechanical pressure, this can initiate fungal spoilage
* Fruits and vegetables also offer a variety of natural or accidental openings → **Wounds** are a common site for spoilage microorganisms OR **Natural openings (blossom end, stem scars**, etc.) are also a potential site for spoilage organisms to penetrate tissues
82
WHY it is better to buy whole lettuce and not individual leaves in the package)
Some bacteria are able to gain direct entry to plant tissue, although, this has only received a lot of attention as it applies to pathogenic bacteria (the bacteria is able to enter in the material of leafy greens
Like e.coli and salmonella
83
Why fruits and vegetables are a good source for microbial proliferation
•Fruits and vegetables have a water content \>95% and contain a significant amount of nutrients essential for microbial growth, they also have an abundance of nutrients essential for microbial growth
84
Why fruits and vegetable are not good place for bacteria, who can grow instead?
* The main limitation preventing the growth of bacteria in fruits and vegetables is the pH (as low as pH 2.0 in some citrus fruits)
* **Spoilage of low-pH fruits is caused by molds and yeasts, which are more tolerant to high acidity**
85
How can fruits and vegetables naturally protect themselves from microbes?
* Fruits and vegetables also have antimicrobial compounds like tannins and phenolic compounds (i.e. saponin in tomatoes), sulfur-derived antimicrobials (onions and garlic), or terpenoids in carrots
* **Phytoanticipins** may be involved in plant resistance
* **Phytoalexins** are small molecules produced by plants in response to PAMPs on bacteria
86
What storage temp is recommended for F&V
* Storage at close to 0C is recommended for most fruits and vegetables
* Except for produce from tropical regions that can suffer from chilling injuries (these should be stored at ~10C)
87
What conditions by human cna be applied to F&V to limit microbial proliferation
1. •Control of temperature, relative humidity, and composition of the gaseous atmosphere can reduce respiratory activity of fruits and vegetables, which delays ripening, and prolongs shelf life
2. Modified atmosphere also helps reduce the growth of microbes, and slow aging via ethylene
3. A relative humidity of 90% is recommended for most fruits and vegetables
88
or what vegetables there is an exception about storage conditions of 90% humidity
* There are a few exceptions like garlic and onions
* High humidity encourages the growth of microbes
89
What are the form of nuts? how they can be protected
* The edible portion of the nut can be called the seed, kernel, or meat
* Seed coats are present on all nuts, and can be as thin as paper (peanut), or thick and hard (coconut)
* All nuts have a rigid outer casing or shell
90
How most nuts are processed? Is bacteria an issue for nuts? What spoils nuts?
91
What is the issue with peanuts? (name a particular microbe)
92
Cereal grains and potential of microbial proliferation
93
There are two types of fungi that can invade cereals: name two groups and put different fungi in those types, and why each type occur and can do to the grain
## Footnote
* Molds that infect the grain before harvest are known as **field fungi** while molds that infect grain after harvest are called **storage fungi**
* **Field fungi** include ***Alternaria, Cladoporium, Fusarium*****, and*****Helminthosporium**.* These molds require a water activity above 0.9 and are encouraged by low temperatures and high precipitation. Field fungi, under the right conditions, can damage the grains even to the point of total crop loss
* Storage fungi include ***Aspergillus, Rhizopus*****,*****Mucor, Wallemia,*****and** ***Pennicillium.*** Growth occurs as a result of improperly dried grains, and high mycotoxin levels can result
94
Talk about spoilage of bread: what is done to it and what is the microbes that do the spoilage
