Semester 1 Flashcards
1
Q
What is not produced in mammary gland secretory cells but happens to be in these cells?
A
Immunoglobulins
2
Q
Is the amount of milk regulated by microbes present in the mammary gland?
A
No
3
Q
What biological molecule is not considered as a primary natural microbial system in milk?
A
Hypothiocyanite
4
Q
Is heat treatment the critical step in maintaining the microbiological quality of milk?
A
True
5
Q
Is streptococci the main bacterial group associated with cows mastitis?
A
True
6
Q
What cfu / ml of PCA plates is considered as good in raw milk?
A
1000
7
Q
What of the following preservation methods cause less nutritional damage to milk?
A
Pasteurisation
8
Q
Honeybees poses microbes in their guts that are involved in honey fermentation
T or F
A
True
9
Q
What part of the body do bees use to make royal jelly?
A
Head
10
Q
What is the main microbiological concern with regards to the safety of honey?
A
Clostridium
11
Q
Fermented foods are foods that have been subjected to the action of microbes in order to bring a desirable, beneficial change.
What are the benefits of fermentation?
A
- Preservation - extend shelf life vs raw material
- Perception - improved aroma and flavour characteristics
- Nutrition - increased vitamin content and digestibility
- Removal of toxic or allergic compounds - cassava, milk
12
Q
Lactic acid bacteria are able to concentrate solutes or move water to create an osmotic balance between the cytoplasm and external environment.
What are lactic acid bacteria?
A
Gran positive, non spore forming bacteria
Rods or cocci
Aerotolerant anaerobes
Catalase and oxidase negative
No functional Krebs cycle as they don’t have cytochromes
Strictly fermentative - use of glucose
Production of lactic acid!
Grow at different temps
Cope with high salt concentrations
13
Q
What does oxidase positive mean?
Why don’t lactic acid bacteria have this oxidase?
A
Means that the bacterium contain cytochrome c oxidase - essential to generate energy via the electron transfer chain in presence of oxygen
Lactic acid bacteria test negative for oxidase. They use sugars (glucose) to obtain energy, anaerobic glycolysis
14
Q
What is a mesophilic lab?
A
Fermentation’s between 20 and 30 degrees
Cheese, fermented meats and veg eatables
Buttermilk
Sour cream
Diacetyl - cheesy, buttery
Eg. Lactococcus, leuconostoc
15
Q
What is a thermophilic lab?
A
Fermentation’s between 35 and 42 degrees
Stirred or set yoghurts
Acetaldehyde - fruity, sweet
Eg. Lactobacillus, streptococcus
16
Q
How are lactic acid bacteria preserved?
A
Low pH - in bacterial cytoplasm the acid dissociates to reduce cytoplasmic pH and kill bacterium
Bacteriocins
Hydrogen peroxide
Ethanol
Nutrient depletion
Low redox potential - fermentation of lactose and consumption of oxygen by LAB results in decrease of redox potential - creating an anaerobic environment where only obligatory or facultative anaerobic microbes can grow
17
Q
What are the bacteriocins? (LAB)
A
They are riobosomally synthesised anti microbial peptides
Class 1: modified bacteriocins, post translational modifications. NISIN - lactococcus
Class 2: non modified bacteriocins: disulphide binds. PEDIOCIN - pediococcus. ENTEROCIN - enterococcus
Class 3: big and thermo sensitive bacteriocins
Class 4: circular bacteriocins
18
Q
Hydrogen peroxide producing lactic acid bacteria include several lactobacillus species.
H2O2 is mainly produced in central carbon and energy metabolism by oxidases. Why can LAB cope with accumulation of H2O2?
A
Due to the presence of hydrogen peroxide scavenging enzymes such as NADH peroxide.
When LAB are exposed to high levels of oxygen, hydrogen peroxide is produced to accept electrons from sugar metabolism. This has a sparing effect on the use of pyruvate or acetyl aldehyde as electron acceptors.
So sugar metabolism in aerated cultures in LAB can be different from that in unaerated cultures!
19
Q
Why are fermented milk products made?
A
Easy to produce and generally safe. Only contamination is with fungi and Yeasts
Extends shelf life due to anti microbial properties of LAB
Appealing due to flavour compounds (diacetyl, acetaldehyde) and texture (casein precipitation and EPS formation)
20
Q
What are probiotics?
A
Live microbes which when given in adequate amounts confer a health benefit on the host
21
Q
Cheese is consolidated curd of milk solids in which fat is entrapped by coagulated casein.
What is the role of lactic acid bacteria during cheese making?
A
Lactic acid production - assists in rapid coagulation of casein. Aids in the shrinkage of the curd and whey expulsion
Other activities - citrate fermentation produces flavour compounds (diacetyl) and CO2
Production of proteolytic and lipolytic enzymes to aid maturation and aroma formation
22
Q
What are the microbial cultures used for making cheese?
A
Starter cultures - LAB assist with coagulation by lowering the pH before rennet addition. They also contribute to desirable flavour and texture to help prevent growth of spoilage organisms and pathogens.
Typical starters include Lactococcus lactis and Lactobacillus helveticus
Adjunct cultures - microbes that are used to enhance flavour, texture and colour
23
Q
What are the cheese production stages?
A
Pasteurisation
Addition of starter (ripening)
Addition of rennet (coagulation)
Settling of curd (pitching)
Separation of whey
Milling and salting
Pressing
Maturation (soft or hard)
24
Q
What can spoil yoghurt and cheese?
A
Yoghurt may contaminate with yeast and fungi once opened
Some anaerobic bacteria like Clostridium may ruin cheese ripening / maturation
High levels of LAB might increase production of lactic acid and EPS, resulting in very sour slimy product
25
What are the essential ingredients of beer?
Malted barley - provides sugars
HOPS - obtained from the flower of hop vine. Provides bitterness to balance the sweetness of malt
Yeast - responsible for fermentation
Water - beer is 90% water
26
What are the brewing steps?
Milling - produces useful hydrolytic enzymes
Mashing
Wort separation - enzymatic conversion of starch to maltose, proteins to aas, extraction of hop flavours and removal of spoilage organisms
Wort boiling
Cooling, aeration
Fermentation
Yeast separation - cask condition, keg, bottle, pasteurise (use of maltose to produce alcohol and CO2)
27
What happens during the Malting brewing step?
To promote the production of hydrolytic enzymes to facilitate starch breakdown into sugars like maltose as well as the degradation of soluble constituents to low molecular weight compounds that will be used by yeast to grow and multiply.
Glucanases break down cellulose surrounding the starch to make it more accessible
Amylases start breaking down starch to produce maltose
Proteases degrade reserve protein to an appropriate mixture of amino acids
28
Beer is microbiologically robust due to the presence of ethanol and low pH but it can spoil and give off odours / flavours and hazes
What can cause beer to spoil?
Cask contained ale is more susceptible to contamination
LAB steal sugars to produce lactic acid instead of alcohol
Zymonomas mobilis: gram negative bacterium that produces ethanol and CO2 out of sugar. Also acetaldehyde and hydrogen sulfide which is associated with rotten apple smell
Acetic acid bacteria may oxidise sugars and ethanol to produce acetic acid
Enterobacteria may generate sulphur compounds
29
LAB are the … microbes involved in food fermentation’s
Most popular
30
LAB fermentation’s extend shelf life and improve … properties
Organoleptic
31
The … between L. Delbrueckii and S. thermophilus in milk results in yoghurt production
Mutualism
32
In cheese, LAB such as L. Lactis and L. Helveticus are used as … to initiate the coagulation of milk.
But other microbes including LAB, Yeasts and fungi are added … to enhance flavour, texture and colour
Starters
Later on
33
In beer, yeasts mainly Saccharomyces are responsible for alcoholic …
Fermentation
34
Yeast and LAB work in … in order to produce other alcoholic products such as wine, kefir and kumis
Symbiosis
35
What is HACCP?
A system that identifies, assesses and controls the hazards that are associated with food production to prevent potential problems before they happen
HACCP stands for: Hazard analysis and critical control points
36
Why is HACCP important?
To control potential hazards in food production
To assure products are safe in the food industry
Focuses on the health safety issues of a product and NOT the quality of the product
37
Examples of biological hazards? (Bacteria, viruses, parasites)
Salmonella, Campylobacter, Norovirus, E.Coli, Clostridium
38
Examples of chemicals hazards
Naturally occurring chemicals - mycotoxins
Intentionally added chemicals - preservative sodium nitrate
Unintentionally added chemicals - pesticides
39
Examples of physical hazards
Insects, hair, metal, plastic, glass, dirt
40
What are the tasks involved in development of the HACCP plan?
1. Assemble the HACCP team
2. Describe the food and its distribution
3. Describe the intended use and consumers of the food
4. Develop a flow diagram which describes the process
5. Verify the flow diagram
41
What are the 7 principles of HACCP implementation?
Hazard analysis
Determine the critical control points CCP
Establish critical limits
Critical control point CCP monitoring
Corrective actions
Establish verification procedures
Record keeping procedures
42
What is a critical limit?
A maximum / minimum value where a parameter must be controlled at a CCP to prevent the occurrence of a food safety hazard
43
When there is deviation from critical limits, corrective actions are taken to:
Determine and correct the cause of non compliance
Determine the disposition of non compliant product
Record the corrective actions that have been taken
44
HACCP plan
HACCP team and assigned responsibilities
Description of food, it’s distribution, intended use and consumer
Verified flow diagram
45
What is thermal processing of food?
Food preservation by heat treatment
The aim is to kill micro organisms using heat but it can be detrimental to the nutritional content and sensory properties of food
46
What is the primary objective of heat treatment?
To improve safety (eliminate pathogens)
47
What is the secondary objective of heat treatment?
To extend shelf life (reduce load of spoilage organisms)
48
What are the types of heat treatment?
Blanching / cooking
Pasteurisation
Appertisation - retorting (canning), UHT / aseptic packaging
49
Who is pasteurisation named after?
Louis Pasteur
50
What is pasteurisation?
Aims to kill pathogens and to extend shelf life by reducing microbial load
Heat usually below 100 degrees and additional preservation needed (chilling)
51
What is appertisation and who is it named after?
Refers to the process where only organisms that survive processing are NON pathogenic and incapable of developing within the product under normal storage conditions
Nicolas Appert
52
What is the aim of appertisation?
Aims to kill microorganisms so that any that remain cannot grow in the product under normal storage (commercial stabilisation)
Uses temps above 100 degrees and results in ambient stable products
53
What are the types of appertisation?
Ultra high temperature (UHT) 135 degrees for 1s in aseptic package (ambient)
Canning 115 degrees for 25-100 mins in cans /jars (ambient)
54
What is sterilisation?
Complete destruction of all microorganisms
Very harsh treatment, dramatic changes in food quality
Essential in clinical settings (surgery etc)
55
Methods for packaging thermally processed foods
In package sterilised products (cans, bottled products)
UHT or aseptically processed products (long life milk, fruit juices and soups)
56
What are the 4 steam based processes used in sterilising food?
Saturated steam - direct steam heating
Water immersion - indirect steam heating
Water spray - indirect steam heating
Steam air - direct steam heating
57
General considerations for canning
Nature of food (ph, composition, viscosity(
Heat resistance of organisms
Storage conditions after thermal processing
58
Kinetics of thermal killing
Heat kills bacteria logarithmically - by protein / nucleic acid denaturation and membrane disruption
If 90% are killed in 1st minute then 90% of those still alive will die during 2nd minute then 90% of those still alive will die during 3rd minute etc…
59
Spores are more heat resistant than…
Vegetative cells
60
Bacteria subjected to heat are killed at a rate that is .. to the number of organisms present
Proportional
61
What is the D value?
Decimal reduction time
The time needed to reduce a population of microorganisms by 90% (1 log cycle) at a specified temp and in a specified medium
For example, if the initial population was 100 CFU/ml, 10CFU/ml would remain after 1 log cycle reduction
Measure of heat resistance of microorganisms
D values are calculated from the SLOPE of the curve of survivors vs time
A d value of 1 min at 72 degrees means that for each minute of processing at 72 degrees the bacterial population of target micro organisms will be reduced by 90%!
62
What is an application of D values?
Allow accurate predictions of the rate of thermal lethality
63
What is the Z value?
The amount of change in temp that will shift the D value in either direction by 90% (1 log)
A measure of resistance of an organism to temp changes - smaller Z values indicate greater sensitivity to increasing heat
64
What does the z value reflect?
Reflects the temp dependence of the reaction
Reactions with small z = highly temp dependant
Large z = require larger changes in temp to reduce the time
A z value of 10 degrees is typical for a spore forming bacterium
65
What is the F value?
The number of minutes required to kill a known population of microorganisms in a given food under specified conditions
F value is usually set at 12D values to give a theoretical 12 log cycle reduction of most heat resistant species of mesophilic spores in food can
Eg if a killing process has an F121 of 4, this means that it produces an equivalent killing to a good heated to 121 degrees for 4 minutes
12D process is for c botulinum spores used fo assess public health protection for low acid canned foods > a heavy load of spores would be 10^12 spores
So a 12D reduction time would provide 1 in a billion chance that a spore would survive in a canned food
66
How a particular microorganism responds to temperature is defined by 3 cardinal points
Minimum, optimum, maximum temps for growth
67
Microbial growth occurs from -8 to over 100 degrees but:
Some organisms have specific temp requirements within this range
Food is only stored at certain temps
Mesophiles and pyschrotrophs are problematic in food
68
Below -10 degrees…
NO microbial growth can occur
69
Chilled foods 0-5 degrees
Changes flora to slow growing psychrotrophs which will eventually spoil food
Pseudomonas and entrococcus grow well and cause spoilage
Listeria, salmonella, b cereus and yersinia are of particular concern
70
Frozen foods < - 18 degrees
Maintains sensory and nutritional properties
Does not sterilise food
Dependant on both temp and aw
71
Refrigeration
Increasing use today: consumer demand for high quality foods with shorter cook times
Little change in flavour, colour, taste, shape or texture
Food stored between 0-5 degrees
Psychotropic pathogens can grow
Acidic proteins rise due to cold shock (ssDNA breaks, membrane stiffness)
72
Freezing
-0.5 to -3 degrees normally
Gram negative bacteria are more susceptible
Psychrophilic and psychotropic organisms are more tolerant to freezing
Not sterile food
Textures usually better
73
What is Non thermal preservation methods (new developments)?
The use of physical methods of inactivation that do not use heat and thus the effects on the nutritional and sensory properties of foods are slight
74
What is irradiation?
Exposure of food to electromagnetic radiation to kill microorganisms
75
What is high hydrostatic pressure (pascalisation)
Exposure to high pressure (400-1200 Mpa) to kill microorganisms
76
What is pulsed high electric field treatment (PHEF)?
Inactivation of microorganisms after exposure to electric fields (15 kV /cm)
77
What is pulsed light?
Successive repetition of high power pulsed of broadband emission light
78
What is ultrasound?
Generates alternating high /low pressure
At low pressure small vacuum bubbles are created that collapse violently during the next high pressure cycle (cavitation) to produce very high temps (-5000K) and pressures (-2000 atm)
79
What is cold plasma technology?
Inactivates target organisms by releasing the stored energy
80
What is high pressure processing (HPP)?
Cold pasteurisation of already sealed products
Introduced into a vessel under high hydrostatic pressure (200- 800 MPa) transmitted by water to kill microorganisms
81
Electromagnetic radiation used in food preservation:
Microwave
Ultraviolet
Ionising radiation
The higher the frequency the more energy the radiation contains
82
E = hv
H = planck’s constant
V = frequency of radiation
83
Preservation by exposure to microwaves
Microwaves excite water molecules which get pulled back and forth at a rate of about 2.5 billion times per second by the electric fields - generates friction and heat
Microwaves can only penetrate 3.5 to 5cm so centre of food is cooked by heat conduction
Main use is quick cooking, thawing, pasteurisation of fruit products
84
Preservation by exposure to UV light
Most lethally effective at wavelength of 260nm
Strong absorption by nucleic acid bases
Products are dimers between adjacent pyrimidines
Main uses: clean air in food rooms / sterilisation of chill rooms and packaging materials
85
Preservation by exposure to ionising radiation
IR contains sufficient energy to ionise molecules as it:
Directly impairs critical cell functions or components, DNA damage
Indirectly impairs cell function via free radicals from water
(H, OH radicals are responsible for 90% of DNA damage)
86
Types of electromagnetic radiation used to preserve foods
Focused electron beam
X rays
Y (gamma rays)
87
What is gamma irradiation?
A safe and effective process that can be used for controlling microbial contamination of dry food ingredients
Irradiation is chemical and residue free, has little or no effect on appearance, flavour, texture or aroma
88
What is electron beam irradiation (EBI)?
Uses low dose ionising radiation in crops or food to eliminate microbial contamination
Low cost, environment friendly, time effective
Extends shelf life
89
Electron beam irradiation
Can inhibit microbial growth in food
When exposed to EBI, microorganisms generate energy transfer within their body, resulting in destruction of chemical and molecular bonds
90
Milk is the perfect environment for bacteria to …
Profilerate
91
Why are lactic acid bacteria abundant when there’s high lactose content?
They use it for fermentation / proliferation
92
Water buffalo have a very high fat content in their milk.
What is their milk used to make?
Mozzarella
93
How is milk produced?
Lactation
94
What is the udder?
What is the alveolus lined with?
A highly developed and modified sweat gland
Milk producing epithelial cells
95
What is meat comprised of?
Water - 75%
Protein - 19%
Fat - 2.5%
Carbohydrate - 1.2%
Inorganic compounds - 0.65%
96
Characteristics of meat
Most b vitamins in useful quantities
Water activity =0.99
Redox potential - mostly facultative anaerobic
Ph = 5.2 to 7
97
What is the production process of meat?
Farm > transport > lairage > slaughter > dressing > chilling > cutting and boning
98
What are the intrinsic bacteria that can contaminate meat?
Commensal bacteria naturally present in muscular tissues and blood vessels
99
What are the extrinsic bacteria that can contaminate meat?
* spoilage or pathogenic bacteria that contaminate meat during slaughter, processing and storage
Faeces
Hide contact
Spilling of bodily fluids
Aerosols or sprays
Contaminated hands or equipment
Abattoir workers
Inappropriate preservation methods
100
Examples of facultative anaerobes that can contaminate meat?
LAB: natural gut micro flora - eg enterococcus, lactobacillus, pediococcus
Staphylococcus (hide)
Shewanella (poultry)
101
What are examples of aerobes that can contaminate meat?
Pseudomonas
Acinetobacter
Moraxella
Micrococcus
102
Fungi and yeast can also …the meat surface
Contaminate
103
How do carbohydrates lead to meat Spoilage?
Glycogen and glucose > CO2 > organic acids (lactic acid) > sour - cheesy by LAB
LAB
Enterobacteria
104
How do lipids contribute to meat spoilage?
Aldehydes and ketones > fruity sweet
LAB
105
How do proteins contribute to meat spoilage?
Collagen, actin, myosin, myoglobin > short peptides, amino acids, amines (bitter putrid) > production of extracellular polysaccharides EPS = slime
Gram negative aerobes
Pseudomonas
106
What bacteria does raw fresh meat contain?
Campylobacter
Salmonella
E. coli
107
How can meat be preserved ?
Cured meats (LAB)
Fermented meats (LAB)
Aerobic chill storage
Vacuum packing
Modified atmosphere packing
Canning (clostridia)
Freezing
108
What are the meat borne pathogens and where are they found?
Salmonella species - pork and chicken
E. coli O157:H7 - beef
C jejuni - chicken
L monocytogenes - environment
C botulinum - canned meats
109
What is the FSA meat hygiene service and what does it include?
Responsible for providing verification and inspection in approved slaughterhouses
Animal welfare at slaughter, animal identification
110
What is the trend of bacterial counts from fish?
Lower counts on fish from clean, cold waters
Higher counts on fish from tropical, sun tropical and polluted waters
But more psychotrophs on fish from cold waters
111
What bacteria are found in fish?
Most are gram negatives
Eg pseudomonas, acinetobacter, aeromonas, shewanella, vibrio, flavobacterium and cytophaga
112
Spoilage of fresh fish vs fresh meat
Spoilage beings immediately after death
Ph higher so less restrictive to bacteria
Less carbohydrates so protein / amino acids used by bacteria earlier on = more putrid volatiles
Cold water: higher proportion of psychrotrophs = 80% of spoilage
113
How does indole production spoil fish?
Spoilage bacteria convert tryptophan into indole which has intense faecal odour!
114
How does formation of ammonia spoil fish?
Spoilage Bacteria deaminate free amino acids to release ammonia
Worse in sharks and rays as they contain high levels of urea that can also be converted into ammonia
115
How does the formation of TMA spoil fish?
Spoilage bacteria convert trimethylamine N oxide TMAO and odourless osmolyte into the foul smelling trimethylamine
116
Examples of fish borne disease
Vibrio cholerae
Vibrio parahaemolyticus
Vibrio vulnificus
Enteric viruses (Noro virus)
117
What is scombroid fish poisoning?
If fish is not chilled properly after being caught, bacteria begin to convert histidine into histamine
118
What is shellfish poisoning?
Bivalve molluscs are filter feeders and therefore accumulate toxins produced
119
What is milk?
Emulsion of fat and water containing dissolved carbohydrates, proteins vitamins and minerals
They are transported to the mammary gland to provide complete nutrition and immunological protection to the new born
120
What is the composition of milk?
Water - 87%
Protein - 3.5%
Fat - 4%
Lactose - 4.7%
Minerals - 0.8%
Water activity = 0.99
Ph = 6.4-6.6
121
Steps of milk formation
Solution with lactose dissolved in water
Emulsion of spherical fat droplets
Suspension of Casein micelles
122
How is milk produced via lactation?
After digestion, nutrients are absorbed from the intestine into bloodstream
Nutrients are then delivered to the udder, which has a high supply of blood to allow large volumes of milk to be produced
Nutrients are used to produce milk that is accumulated and then secreted
123
How is milk formed?
Milk secreted from epithelial cells into alveoli
Water, minerals, vitamins and immunoglobulins can pass through cell membrane from blood stream
Proteins, lactose and fat are produced in secretory cells and transported into lumen
Amount of milk is regulated by lactose by influencing the osmotic pressure between blood and alveoli
124
How do bacteria get from the cows gut to the newborn?
Dendritic cells go across gut epithelium to directly take up bacteria from gut lumen
Live bacteria can then spread to other locations through blood stream
Dendritic cells can also migrate via Entero Mammary Pathway - so bacteria arrive at mammary gland
This explains the abundance of maternal gut bacteria in colostrum and Breast milk
Milk microbiota continue travelling until they reach infant gut
125
What are the natural milk antimicrobial systems?
Antibodies - IgA and IgG
Lactoperoxidase - generates short lived oxidised intermediates like hypothiocyanite that are effective in killing aerobic and anaerobic bacteria
Xanthine oxidase - produces antimicrobial radicals like superoxide, nitric oxide and peroxynitrite
Lysozyme - degrades bacterial cell wall of gram positives
Lactoferrin - binds iron and withholds
126
Milk distribution:
Historically vs Now
Historically:
No temp control
Short distribution chains
Preservation not that important
Now:
Industrialisation
Long distribution chains, from farms to urban centres
Preservation is essential
127
What are the steps in milk production?
Milk production > milk collection > milk chilling and storage > milk packaging (heat treatment) > transport > consumer practices
PREVENT MASTITIS and microbial hazards
128
Important risk factors in milk production
Heath status, housing and herd size, waste management
Milk practices, mastitis control measurements m
Efficiency of chilling practices, personal hygiene and sanitisation
Maintenance of chill temps, equipment
Efficiency of pasteurisation
Adherence to use by dates
129
What is inflammation of the mammary glands due to?
Increased levels of bacteria and somatic cells, with the subsequent decrease in milk quality
It causes MAJOR losses in milk production
Caused by 137 different organisms but just 5 cause over 80% of infections: staph aureus, streptococcus and E. coli
130
How to prevent infections of the mammary gland?
Provision of clean litter
Rapid removal of slurry
Shave udders, trim tails
Wash teats with disinfectant
Keep parlour floor clean
Clean teat cups
131
Mastitis detection - what are the main indicators of milk quality?
Somatic cell count SCC - somatic cells are a mixture of milk producing cells and immune cells
<100 000 cells/ml = no infection
> 200,000 cells/ml = mastitis
REGULATIONS EU
Plate counts
PC <100 000 mesophiles per ml
SCC < 400,000 cells per ml
132
Raw milk contains potentially many pathogens of significant concern.
What are the spoilage organisms?
Psychotrophs: pseudomonas, flavobacterium, alcaligenes
Some coli forms
133
Pasteurised milk contains usually few pathogens of low concern.
What are the spoilage organisms?
Psychrotrophs
Spore forming pschrotrophs
Bacillus spp
134
What can cause spoilage in the carbohydrates, proteins and lipids that make up milk?
Carbohydrates - lactose > lactococcus lactis > lactic acid > sour
Lipids - short chain fatty acids > lactococcus, aerococcus, acinbacter > rancid flavour
Proteins - Caseins, whey proteins > lactococcus, enterobacter, serratia, aerococcus, bacillus > short peptides, amino acids and amines > bitter, putrid
135
What may refrigerated raw milk contain that could compromise the quality of dairy products during storage?
May contain psychotropic bacteria that produce thermoresistant exo proteases and lipases which can compromise quality
136
Microbial hazards in milk today
Staph aureus - vomiting, mild
Campylobacter jejuni - severe gastroenteritis
Salmonella - severe gastro
E. coli - severe gastro
Listeria monocytogenes - severe, systemic infection in vulnerable
Mycobacterium bovis - tuberculosis
Brucella abortus - brucellosis
Coxiella burnetii - Q fever
137
What pathogens could be found in raw milk?
L monocytogenes
Salmonella
E. coli
138
Milk can only come from herds that officially … and … free
TB
Brucellosis
139
What is honey?
A sweet, viscous substance made from floral nectar by bees and some related insects
Honey is produced after ingestion, enzymatic activity, regurgitation and water evaporation
Water - 18%
Fructose - 40%
Glucose - 30%
Other sugars - 10%
Minerals - 2%
140
Process of honey production by the bee
It goes to their honey stomach (40mg of nectar)
Enzymes break down sucrose into glucose and fructose
Digested nectar is regurgitated, placed in honeycomb cells and left unsealed
Fermentation: LAB and Yeasts (acidity)
Bees flutter their wings to circulate air and evaporate water (sugar concentration increases)
Food supply = energy
Removed by the beekeeper
141
How is bee pollen produced?
It is flower pollen that has been packed by bees, mixes with saliva and sealed with a drop of honey in brood cells
Proteolytic enzymes break down walls of pollen grains to make nutrients more available and to facilitate fermentation
Composition: 50% fructose and glucose, 20-60% proteins, 1-30% fatty acids
Primary source of protein for the hive but also harvested for human consumption
142
How is royal jelly produced?
Secreted by the glands in the hypopharynx (head) and is feed to all larvae, especially the queens
Composition: 67% water, 12.5% proteins, 11% sugars, 10% FA, minerals and vitamins B-C
Nutrition source for larvae but also queens
Marketed as a supplement in alternative medicine but EFSA haven’t found evidence to support the claim of health benefits
Allergic reactions due to its consumption have been reported
143
How is beeswax produced?
By glands in the abdominal segments of bees and used to form cells for honey and pollen storage but also to protect larvae
Composition: esters of FA and long chain alcohols
144
The preservation of honey
Beekeeper pacify bees with smoke - the smoke makes bees less aggressive
Honeycomb is removed and the honey extracted
Honey is filtered and replaced by candy board - sugar water or crystalline sugar to survive winter
Pasteurisation - 63 degrees for 30 min
Packing - consumer
145
Microbes of concern in honey
Come from post harvest handling:
Yeasts, spore forming bacteria, coli forms and clostridia
146
Primary sources of microbial contamination in honey
The microbiota of honeybee products, dust, air, food handlers, cross contamination, equipment
147
Why is honey suitable for long term storage?
Because of its own chemical composition:
Low water activity, high ph, high sugar content and the presence of antimicrobial compounds such as gluconic acid and hydrogen peroxide
148
Fermented foods
Foods that have been subjected to the action of microbes in order to bring a desirable, beneficial change
Originated thousands of years ago
Account for 1/3 of world wide food consumption
149
What are the benefits of fermentation?
Preservation - extend shelf life vs raw material
Perception - improved aroma and flavour characteristics
Nutrition - increased vitamin content and digest ability
150
What gram positive bacteria are produced from the glycolysis pathway?
Lactobacillus
Lactococcus
Pediococcus
Enterococcus
Vagococcus
Streptococccus
151
What gram positive bacteria are produced from the 6 P-gluconate pathway?
Carnobacterium
Leuconostoc
Oneococcus
Weisella
Lactosphaera
152
What does the F ATPase of LAB do?
It confers protection against acidic conditions due to the generation of a proton motive force
This F ATPase increases the intra cellular ph at a low extra cellular ph
153
Yoghurt: milk fermented by LAB
Easy to produce and generally safe > only contamination with fungi and yeasts
Extends shelf life due to anti microbial properties of LAB
154
What is the heat treat step in yoghurt production?
80-85 degrees for 30 min / 90-95 degrees for 5-10 min
Reduces bacterial load
Improved as growth medium
Starts casein denaturation
155
What is the starter in milk production?
Lactobacillus delbrueckii and streptococcus thermophilus
Added in equal numbers
Produce 1% lactic acid, ph 4.2-4.3
156
Incubation step of milk production - 42 degrees
Addition of probiotics
Lactobacillus casei and bifidobacterium
157
Whole hops are added to sweet wort and boiled in the copper to…
Extract bitterness, flavour and aroma from the hops
Inactivates enzymes
Pasteurises wort
Concentrates wort
158
What does Oenococcus do to wine?
Reduced acidity
Increased body - dextrans and glucans (EPS)
Increased flavour complexity - buttery, nutty
159
What are the kombucha fermentation steps?
1. Glucose > ethanol catalysed by saccharomyces cerevisiae
2. Ethanol > acetic acid catalysed by acetobacter aceti
160
Ale yeast fermentation
a- galactosidase
Saccharomyces cerevisiae
Growth 5-40 degrees
Fermentation 12-18 degrees
Top fermenting
Melibiose negative (remains)
161
Lager yeast fermentation
a- galactosidase
S carlsbergensis and s pastorianus
Growth 0-33 degrees
Fermentation 8-12 degrees
Bottom fermenting
Melibiose positive (disappears)
162
Listeria monocytogenes
Gran positive, NON spore forming, motile, facultatively anaerobic, catalase positive, oxidase negative, rod shaped bacterium
Grows between 0-42 degrees with an optimum between 30-35 degrees
Below 5 degrees growth is extremely slow
Growth of ALL strains is inhibited at ph values below 5.5
Organism is ubiquitous in the environment. It has been isolated from fresh and salt water, soil, sewage, decaying vegetation and silage
163
Listeria monocytogenes infections
Rare but often severe with high hospitalisation and mortality rates
Majority of human cases were sporadic and foods related to transmission were ready to eat, extended shelf life (usually refrigerated)
Pregnant woman, very young or elderly and Immuno compromised more likely to be predisposed to infection
Important veterinary problem
Meningoencephalitis most common in adult ruminants (cattle, sheep)
164
Clinical features of Listeria monocytogenes infection
CNS disease (tropism for brain tumour) - meningitis, meningocencephalitis, brain abscesses
Sepsis (most common in compromised hosts)
Endocarditis
Gastroenteritis
Focal infections
Hepatitis
Myocarditis
165
Pathogenesis of listeria monocytogenes infection
Facultative intra cellular pathogen that penetrates the gut either by crossing Peyer’s patches or by invading enterocytes
Listeriolysin O (haemolysin) breaks down lipid bilayer of phagosomal membrane allowing the bacteria to escape from phagosome
Virulence factors - internal ins, phospholipases
166
Escherichia coli
Gram negative, facultative anaerobic, NON sporing, catalase positive, oxidase negative, fermentative short rod
Universal inhabitant of gut of humans and other warm blooded animals
Indicator of faecal contamination
The minimum water activity for growth is 0.95
Mesophile growing from 7-10 degrees up to 50 degrees with an optimum around 37 degrees
Opportunistic pathogen causing a number of infections such as sepsis, gastroenteritis, urinary tract infections, pneumonia and meningitis
167
E. coli infections
People get infected with VTEC by consuming or handling contaminated food or water or through contact with infected animals
Person fo person transmission possible among close contacts (families, nursing homes)
VTEC strains have been found in raw unpasteurised milk and cheese, undercooked beef and fresh produce (sprouts, spinach, lettuce)
Main source is cattle
Meat can be contaminated by faeces due to poor processing during slaughter
Faeces from infected animals can contaminate other foods and water
168
Association with E. coli and foods
Faecal contamination of water supplies and contaminated food handlers are most frequently caused by outbreaks in EPEC, EIEC and ETEC
Outbreaks by EHEC serotype O157:H7 have mostly involved undercooked meat products and raw milk
Cattle are an important reservoir of infection and O157:H7
Outbreaks associated with fermented meats have suggested the ability of EHEC to survive some fermentation and drying processes
Most outbreaks are due to breakdowns of basic food hygiene and a failure to heat / cook products adequately
Outbreaks of EHEC with lettuce and unpasteurised apple juice (acidic)
169
E coli
Cattle and ruminants are main source
Transmitted to humans through: consumption of contaminated food and dirty water, contact with an infected person or animal
Infection can cause acute renal failure and neurological problems (seizures, stroke)
Can cause respiratory illness and pneumonia
Diarrhoea and in some cases bloody diarrhoea
170
What is sensitivity?
Probability of diseased patients (based on gold standard) having a positive result when tested by diagnostic test
171
What is specificity?
Probability of NON diseased patients (based on gold standard) having a negative result when tested by diagnostic test
172
Staphylococcus aureus
Gram positive, catalase positive, oxidase negative, facultative anaerobic coccus forming spherical to ovoid cells around 1um in diameter
Mesophile with a growth temp range between 7 and 48 degrees
Enterotoxin has an optimum production at 35- 40 degrees
Unexceptional heat resistance
Principal habitat is the skin and mucous membranes of warm blooded animals
In humans, associated with the nasal tract where it is found in 20-50% of healthy individuals
173
Staphylococcus aureus infections
MRSA staphylococcus aureus is resistant to methicillin while MSSA is susceptible
It is a relatively mild, short lived illness so staphylococcus food poisoning is more likely to be under reported
Most reported cases are outbreaks related, only a few sporadic cases
Naturally in poultry and other raw meats
Isolated from raw milk due to mastitis
174
Clinical decay ties of staph aureus infection
Short incubation period 2-4 hours - characteristic of an intoxication where illness of the result of ingestion of a pre formed toxin in the food
Mainly nausea, vomiting, stomach cramps
Diarrhoea is reported
Susceptibility varies but less than 1ug of pure toxin has been required to elicit symptoms
175
Pathogenesis of staph aureus infections
Produces more than 20 enterotoxins - short polypeptides
Toxin types A and D are most frequently implicated in outbreaks of food poisoning
Toxins are resistant to gut proteases and are heat stable, being inactivated only by prolonged boiling
They elicit the emetic response by acting on receptors in the gut, which stimulate the vomiting centre in the brain
176
Association with staph aureus and food
Contamination by food handlers due to the high rate of human carriage
As large numbers >10^6 are required for production of enough toxin to cause illness, contamination is necessary but NOT sufficient on its own for an outbreak
Temperature and time conditions must be provided to favour growth
Outbreaks by cheese, cold sweets, custards, cream filled bakery products
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Bacillus cereus
Gram positive, facultatively anaerobic, spore forming rods
Grows over 8-55 degrees, does NOT have any marked tolerances for low ph or aw
Widely distributed in the environment, isolated from soil, water, vegetation, flour, rice, spices, lentils, beans, meat
Common component of transient gut flora of humans!
Cooking removes its competitors, it’s spores survive, germinate and grow
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Bacillus cereus infections
Two types of food-borne illness:
Diarrhoeal syndrome - relatively late onset of 8-16hr after food consumption and lasts for 12-24 hr
Abdominal pain, profuse watery diarrhoea, nausea and vomiting
Emetic syndrome:
Rapid onset, shirt incubation period of 0.5-5hr
Nausea and vomiting
Both syndromes are caused by distinct enterotoxins
179
Diarrhoeal syndrome of bacillus cereus infection
Haemolytic enterotoxin HBL (proteins B, L1 and L2), a non haemolytic enterotoxin NHE and cytotoxin K produced by about 40% of strains
180
Emetic syndrome of bacillus cereus infections
The emetic toxin, cereal idea is a 1.2kDa cyclic peptide that is acid and best resistant
The toxin is produced in the food in the late exponential to stationery phase of growth and acts by binding to and stimulating the vagus nerve
181
Association with bacillus cereus and food
The ability to produce spores resistant to factors like drying and heat, means that food poisoning bacilli and widely distributed in foods
The emetic syndrome is related with starchy products like rice and pasta
It’s association with rice is called the Chinese restaurant syndrome
Rice is prepared in bulk in advance. Spores of the heat resistant serotype 1 survive pre cooking and produce the emetic toxin during storage
Would be prevented by chilling to below 8 degrees but the rate of cooking in the centre of cooked rice can be slow enough for growth snd toxin production
Reheating rice prior to serving won’t inactivate toxin and ended product safe!
182
Clostridium botulinum
Gram positive, motile with flagella, obligately anaerobic, spore forming rods
It causes botulism
8 toxins are recognised (A,B, C1, C2, D, E, F and G - but C2 is not a neurotoxin) a single strain of c botulinum will usually only produce 1 type
Group 1 strains are not psychrotropic and therefore are of little concern in adequately refrigerated products
183
Clostridium botulinum
Group 2 strains are greater hazard in chilled foods
Most cases in humans are due to types A, B or E
Group 3 strains producing toxin types C and D are associated with illnesses in animals and birds
A ph around 4.7 is the absolute minimum - practical implications in the canning industry
184
Clostridium botulinum infections
Foodborne botulism
Commonly 12-48hr symptoms
Vomiting, constipation, double vision, difficulty in swallowing, dry mouth
Surviving patients may take as long as 8 months to recover fully
The mortality rate is high 20-50%
185
Pathogenesis of clostridium botulinum infections
Ingestion of exotoxin produced by C botulinum growing in food
The botulinum toxins are neurotoxins, they affect the cholinergic nerves of the peripheral nervous system
Mortality rate is high but depends on the toxin type, the amount ingested, the type of food and speed of treatment
Botulinum toxins are the MOST toxic substances known, with a lethal dose for adults of 10^-8
186
Association with clostridium botulinum and food
4 common features are discernible:
1. The food has been contaminated at source or during processing with spores or vegetative cells of c botulinum
2. The food receives some treatment that restricts the competitive micro flora
3. Conditions in the food (temp, ph, Eh, aw) are suitable for growth of c botulinum
4. The food is consumed cold or after a mild heat treatment insufficient to inactivate toxin
187
Viral foodborne diseases
Norovirus and hepatitis A cause the most significant foodborne illness and outbreaks as they are highly contagious
Rotavirus is major cause of diarrhoea
Hepatitis E has been associated with waterborne infections and foodborne outbreaks
Adenovirus, astrovirus, sapovirus, tick borne encephalitis and avian influenza H5N1 may also cause viral infections where food is a vector
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Norovirus
Diverse group of non enveloped viruses causing sporadic cases and epidemic outbreaks
Primary route of transmission is person fo person contact via the faecal oral and vomit oral routes and indirectly through food, water and environment
Self limiting disease, 12-48hr up to 3 days with a low infection dose of 10-100 virus particles
Nausea, vomiting, diarrhoea, abdominal pain
Prolonged virus up to 8 weeks in asymptomatic and Immuno suppressed
Headache and low grade fever may occur
189
Mycotoxins
Naturally occurring toxins produced by certain fungi (moulds) and can be found in food
Moulds grow on different crops and food (cereals, nuts, apples, dried fruits, coffee beans) and often under warm and humid conditions
Can cause a variety of adverse health effects and pose serious health threat to humans and livestock
Adverse health effects range from acute poisoning to long term such as immune deficiency and cancer
190
ETEC E. coli
Heat stable ST withstands heating at 100 degrees for 15 min, acid resistant
Heat labile LT toxins inactivated at 60 degrees after 30 min and at low ph
191
EIEC E. coli
Invades and multiplies within colon epithelial cells (ulceration, inflammation)
192
EPEC E. coli
Adhere to enterocyte membrane producing attaching and effacing lesions
193
EHEC - E. coli O157:H7
Cytotoxins (verotoxin) VTI and VTII (shiga toxin)
194
Food borne and waterborne diseases worldwide
Globally 1.7 billion cases of diarrhoeal diseases per year
600 million ppl fall ill after eating contaminated food
420 000 people in the world die every year by food done diseases
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Foodborne diseases
Campylobacter most common foodborne pathogen
Clostridium perfringens 2nd most common pathogen
Norovirus 3rd most common pathogen
Salmonella causes the most hospital admissions
Poultry meat food most linked to cases of food poisoning
After poultry, vegetables, fruits, nuts and seeds cause the second highest number of cases
196
Chemical agents of food borne disease
Heavy metals - lead, cadmium and mercury
Persistent organic pollutants - polychlorinated biphenyls and dioxins
Naturally occurring toxins - mycotoxins, marine bio toxins
197
Parasites - agents of foodborne disease
Animal or fish parasites - cryptosporidium Parvum, giardia lamblia
198
Micro organisms - agents of foodborne disease
Bacteria - most frequent cause
Viruses - hepatitis A/E, norovirus, norlwalk
Fungi - aflatoxins
Prions - BSE or mad cow disease , vCJD in humans
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Modes of bacterial food poisoning
Infection - colonisation of the GI tract with a living pathogen
Invasive pathogens - invade epithelial cells eg salmonella
Non invasive pathogens - colonise GI tract but DO NOT invade epithelial cells eg E. coli O157:H7
Intoxication - toxin produced in the food and this alone causes the disease
Staph aureus alpha toxin and c botulinum
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Clostridium perfringens
Gram positive, rod shaped, anaerobic, spore forming
Environmentally ubiquitous
Normal component of soil, decaying vegetation, intestinal tract of mammals, marine sediment
Indicator of faecal contamination of water and food
Can double in number every 7-10 min under optimal temp 43-45 degrees and nutrient conditions
Outbreaks mainly associated with catering companies and others who prepare and then improperly store large quantities of food
201
Clostridium perfringens food borne illness
Type A
Toxico infection - enterotoxin
Abdominal cramps and diarrhoea
Mild illness of <24 hrs
Illnesses occur after cooked soups or stews have been left too long at ambient temps that allow spores present to germinate and produce vegetative cells
202
Campylobacter
Gram negative, helical shaped, non spore forming, microaerophilic
Major cause of bacterial diarrhoeal illness
Diarrhoea, vomiting, fever, abdominal cramps
Self limiting disease but 0.1% develop guillain barre syndrome
Raw poultry, beef, offal and unpasteurised milk
Endemic in UK poultry flock
54% campylobacter positive in fresh, whole chicken at retail in UK
203
Campylobacter as foodborne pathogen
29 campylobacter species associated with GIT of animals
C jejuni and c coli cause 90% of human cases
Thermophilc - can grow at 42 degrees but not below 30 degrees
Environmental stressors change the spiral bacilli to coccoid forms - this survival mechanism leads to viable but nonculturable VBNC cells
In the VBNC stage, pathogen maintains its metabolic activity = greater virulence
Ingestion of few hundred cells cause disease
204
Campylobacter epidemiology in UK
Highest in west and north - males more cases than females
Highest in children <5 years
Higher in rural areas with agricultural activity
205
Dioxin crisis to determine poultry related campylobacter enteritis
At week 21 all poultry and chicken withdrawn from shops in Belgium
Significant decline 40% in the number of infections
After 4 week ban was lifted, infections significantly increased
206
Salmonella
Gram negative, rod shaped, facultative anaerobic of enterobacteriaeceae
The infectious dose can be quite low 1-100cfu
Self limiting but many hospital admissions, even death
Diarrhoea, stomach cramps, nausea, vomiting and fever
Illness usually lasts from 4-7 days
S enteriditis can infect eggs
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The global burden of salmonella
Amongst the most successful of human pathogens
1.3 billion cases of salmonella gastroenteritis annually
2nd most common zoonotic disease
€3 billion per year = the economic burden of human salmonellosis
Causes large foodborne outbreaks
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Diseases caused by salmonella
Typhoid fever
Enteric fever
Enteritis
Bacteremia
Asymptomatic carriage
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Reptiles as a vector for salmonella
90% of healthy reptiles carry salmonella
Spread via faeces, urine but also infection via claw scratches and bites
1970s = the great USA turtle associated salmonellaosis epidemic
100 000 cases of reptile borne human salmonellosis per year
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What does the growth / survival of food micro flora depend on?
Properties of food
Processing
Storage conditions
Properties of organisms
211
Impact and significance of food microflora
Food spoilage (undesirable)
Foodborne illness (undesirable)
Fermentation (desirable if purposeful) - improved acceptability, nutrition, preservation
212
Agents of foodborne illness (food safety)
Cause food borne illness
Food is a vector
Limited number of types
Low numbers can cause illness (some <10)
213
Agents of spoilage (food spoilage)
Cause undesirable changes in quality
Changes caused by growth / enzymes
Numerous types cause spoilage
High numbers required (~10^7)
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What are the 4 factors that affect microbial growth?
Intrinsic (properties of the food) - nutrient content, ph, redox potential, water activity, antimicrobial
Extrinsic (properties of the environment) - temperature, relative humidity, gaseous environment
Implicit (properties of organism) - growth properties, interactions
Processing (effects of processing) - washing, slicing and mincing, heat and radiation treatments, preservatives, packaging
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Milk spoilage as an example of the complex process of spoilage
Bacteria (lactobacillus and lactococcus) grow on milk sugars (lactose)
Lactic acid is produced
Ph reduced and lactic acid build up (sour taste)
Acid selects for change in bacterial population, ph drops further and more lactic acid is produced until all sugars depleted
In the very acidic conditions, Yeasts and moulds now use lactic acid for growth and ph rises
Bacteria start fo grow again at higher ph and use proteins as their major nutrient (no sugars) and then primary amines are produced
216
The effect of ph on microbial growth
Ph = -log10 [H+]
[H+] is important for living things as the positive charge alters the charge environment of other molecules in solution
H+ ions can bond to nitrogen or oxygen containing molecules because nitrogen and oxygen have ‘non bonding’ pairs of electrons
Acids are substances capable of donating an H+ to a base
Bases are substances capable of accepting an H+ from an acid
217
Optimum growth ph for some microorganisms
Ph 6-8 = most bacteria
6.2 = shewanella
5.6 = pseudomonas
5-6 = lactobacilli / acetic acid bacteria
4.5 - 6 = most yeasts
3.5-4 = most filamentous fungi
218
Mechanisms for responding to low ph stress in microbes
H+ consumption
Urea production
Removal of H+ (using ATP)
219
Microbial inhibition by weak organic acid
Undissociated lipophilic acid molecules can easily pass via the membrane from an external environment of low ph to the high ph of cytoplasm
At this higher ph, equilibrium shifts in favour of the dissociated molecule, so the acid ionises producing protons which will acidity the cytoplasm
The cell will try to maintain its internal ph but this will slow growth
If external ph is low and the extracellular concentration high, the cytoplasmic ph drops so that growth is NOT possible and cell dies
220
The effect of redox potential Eh on microbial growth
The transfer of hydrogen ions between chemical species determines ph, the transfer of electrons between chemical species determines the Eh
Redox potential Eh is the tendency of a medium to accept or donate electrons to oxidise or reduce
If it accepts electrons, it has a positive potential = oxidising environment
If it donates electrons, it has a negative potential = reducing environment
Strong reducing agents have a HIGH electron transfer potential
Strong oxidising agents have a low electron transfer potential
221
The effect of redox potential Eh on microbial growth
Obligate or strict aerobes need oxygen and high Eh an will predominate at food surfaces exposed to air or where air is readily available
Pseudomonas fluorescens grows at Eh of +100 to +500mV and other oxidative gram - rods produce slime and off odours at meat surfaces
Bacillus subtilis (Eh -100 to +135) produces rope in texture of bread
Obligate anaerobes tend only to grow at low or negative Eh
Obligate anaerobes like clostridia are of great importance in food microbiology!
They can grow in anaerobic conditions (deep in meat tissues and stews, in vacuum packs and canned foods) causing spoilage or botulism by C botulinum
222
The effect of water activity aw on microbial growth
Aw = p divided by p0
A measure of the energy status of water (how much is available / not bound)
Water activity is the vapour pressure of water in equilibrium with the sample (p) divided by the vapour pressure of pure water at the SAME temp (p0)
Pure distilled water has a water activity of exactly 1
Higher aw foods tend to support more microorganisms
Microorganisms differ in their water activity requirements
223
Even if no microbial growth is possible in lower aw ranges, food spoilage is still …
Possible
224
Resistant biological structures
Egg shells
Nut cases
Skins
Hides
225
Natural anti microbial systems
Coumarins - fruits and vegetables
Lysozyme (also in saliva) - cows milk and eggs
Essential oils - herbs and spices
Allicin - garlic
226
The effect of temp on microbial growth
How a particular organism responds to temp is defined by 3 cardinal points - minimum, optimum, maximum temps for growth
Different microorganisms reopens differently to temp
227
The effect of temp on microbial growth
Microbial growth occurs from -8 to over 100 degrees but:
Some organisms have specific temp requirements within this range
Food is only stored at certain temps
Mesophiles and pyschrotrophs are generally of greatest importance
228
Why is it important that freezers are lower than -5 degrees?
Because psychrotophs (facultative for cold) can still grow at this temp
Their minimum temp range is -5 to 5 degrees
229
Effect of temp on microbial growth
Mesophiles with temp optima around 37 degrees are frequently of human or animal origin and include common foodborne pathogens: salmonella, st aureus and cl perfringens
Mesophiles grow more quickly at their optima than psychrotrophs and so spoilage of perishable products stored in mesophilic growth range is more rapid than under conditions
Psychrotophs are found in more diverse range of habitats and so are of greater importance in spoilage of chilled foods
Thermophiles are of far less importance in food micro, but thermophilic spore formers like bacillus and clostridium species pose problems in a few situations
230
Relative humidity
Relative humidity and water activity are inter-related. Relative humidity is a measure of of the water activity of the gas phase
When foods with a low aw are stored in an atmosphere of high relative humidity > water will transfer from gas phase to food
Once microorganisms start to grow, they produce water as end product of respiration. So they increase the aw of their immediate environment so that micro organisms requiring a high aw can grow and spoil a food that was initially micro biologically stable
Storage of fresh fruit and veg needs good control of relative humidity
If it is too low then veg will lose water and become flaccid
If it is too high then condensation may occur and spoilage may start
231
Gaseous atmosphere
Oxygen is the most important gas in contact with food
The inhibitory effect of CO2 on microbial growth is applied in modified atmosphere packaging, carbonated mineral waters and soft drinks
Mould and oxidative gram negative bacteria are most sensitive to CO2 and gram positive bacteria like lactobacilli are most resistant
Some yeasts show considerable tolerance of high CO2 levels and dominate the spoilage micro flora of carbonated beverages
Growth inhibition is greater in aerobic conditions than anaerobic and increases with temp decrease due to increased CO2 solubility at lower temps
Some microbes are killed by prolonged exposure to CO2 but its effect is mainly bacteriostatic
232
The effect of implicit factors on microbial growth
Implicit factors are the inherent growth properties of the spoilage organisms themselves, how they respond to the environment and interact with one another
Growth range - temp and ph requirements, aw
Microbial interaction (how microorganisms influence eachother):
Antagonism - antibiotics, acids
Commensalism - one benefits the other doesn’t
Symbiosis - both partners benefit
233
The effect of processing factors on microbial growth
Processing factors concern the way a food is treated during production and how this influences the presence of microbes
Slicing / mincing - higher exposure to o2 and spread of surface microorganisms to interior of food
Heat treatments - higher temps will destroy microbes
Preservatives - if present will kill or prevent specific microorganisms from growing
Cooling - low temp retards growth
234
The effect of implicit factors on microbial growth
Many moulds can grow well on fresh foods such as meat, but grow more slowly than bacteria so are out competed
In foods where faster growing bacteria are inhibited by factors like reduced ph or aw, moulds are more important in spoilage
The response of microorganisms to changes depends on the physiological state of the organism
Exponential phase cells are almost always killed more easily by heat, low ph or antimicrobials than stationary phase cells
Pre adaptation will decrease the damaging effect of adverse conditions
Pre exposure to a factor increases an organisms resistance to it
235
Chemical preservatives
Preservatives are substances that can inhibit, retard or arrest the growth of microorganisms
They DO NOT include antioxidants or phosphates
Preservatives may be microbicidal and kill the target organism or they may be micro bio static where they prevent them from growing
Higher levels of an antimicrobial are lethal while lower concentrations tend to be microbiostatic
Chemical preservatives are useful only in controlling low levels of contamination and are NOT a substitute for good hygiene practices
236
Nitrite food preservation
Usually in combination with curing
NaCl and nitrite / nitrates action mediated by NO
Nitrites are essential for colour and flavour development in refrigerated food
Nitrosamines an issue (eg bacon and ham)
237
Sulphites food preservation
So2, h2s, na2s2o5
Main use in sausages and wine - stops fermentation, antioxidant, preservative
Destroy thiamine but promote ascorbate retention
Allergic reactions in the sensitive (asthma) a problem
238
Antibiotics food preservation
Must NOT be used in food if have therapeutic application. Strict regulation
Nisin - polycyclic antibacterial peptide from lactococcus lactis
Used to inhibit spore outgrowth in heat processed foods (canned foods, cheeses)
Natamycin (natamax) - from streptomyces natalensis
Anti fungal
Used as a surface preservative for some cheeses and dried sausages
239
Acids food preservation
Benzoic, sorbic, propionic acid and parabens
240
Food preservation by the use of reduced temp
Below -10 degrees NO microbial growth can occur
Chilled food (0-5 degrees) - food stored above their freezing point, changes to flora to slow growing psychrotrophs that eventually spoil food
Freezing (-20 degrees) - maintains sensory and nutritional factors, does not sterilise food, dependant on both temp and aw
241
Food preservation by modified atmosphere packaging
With specialised packing material, the atmosphere around a food can be modified to inhibit microbial growth
242
Vacuum packing - product packed in a vacuum
Decreased o2, increased CO2 inhibits aerobes
Creates a temporary colour change - deoxyhaemoglobin
Used for bulk packing and some retail meats
Concerns about listeria monocytogenes, clostridium botulinum and yersinia entercolitica
243
Modified atmosphere packing MAP
Tailored atmosphere that changes interaction with food:
CO2 inhibits aerobic bacteria and moulds
Low o2: N2 used to to replace o2 to inhibit aerobic spoilage organisms
High o2 used to maintain fresh colour in meat and respiration in fruit / veg
244
Controlled atmosphere packing CAP
Tailored atmospheres which are maintained (steady state)
Used for bulk storage / transport
245
Hurdle technology
Hurdle effect is a method of ensuring that pathogens in food products can be eliminated or controlled = safe for human consumption
Hurdle technology usually works by combining more than one approach
Pathogens have to overcome these ‘hurdles’ to remain active in the food
When the energy needed for biosynthesis is diverted into the maintenance of homeostasis, cell growth is inhibited
When homeostatic energy demands exceed the cells energy producing capacity, the cell DIES!
Most foods are preserved in this manner
246
High acid food (ph <3.7) considerations when canning
Surviving spore forming bacteria will NOT grow
Process relies on inactivation of Yeasts and moulds / maintenance of anaerobic conditions
Low temperature time combinations
247
Acid foods (3.6
Process needs to eliminate spores of Bacillus coagulans, b thermoacidurans, b polymyxa which will outgrow if present
248
Low acid foods (ph >4.5) considerations for canning
It they survive, spores of clostridium botulinum can grow and conditions will be ideal for growth and toxin production
High temp time combinations
249
Pros and cons of steam air retort
Pros
A moderate capital investment
Flexible - can process virtually all types of containers
Energy efficient - utilises a fan for forced convection
Besides the fan, the machine is simple and easy to administer
Cons
Not a good option for high RPM rotary processes - those that exceed 15 RPMs
Machines with rotary processes require significantly more maintenance time and money
The fan is a moving part that adds to the complexity / maintenance of the retort
250
Pros and cons of water spray retort
Pros
A lower capital investment
Flexible
Energy efficient - heat exchanger and pump to re circulate water
Sterilising / cooling water can be reused without chemical treatment for the next process
Storage tanks allow for energy savings by capturing water after sterilisation
Cons
Not good option for rotary processes that exceed 10 RPMs
Requires more maintenance time and money
Come up times are longer for high RPM rotary processes
Cooling times may be extended
251
Pros and cons of water immersion retort
Pros
Can utilise carbon steel vessels
Flexible
Excellent application for rotary processes due to buoyancy of the load
Best application for rotary processes in excess of 10 RPMs
Storage tank allows for energy savings by capturing water after sterilisation
Cons
Higher capital investment if double tank system is used
Virtually impossible to operate manually due to complexity of piping
Machines with rotary processes require more maintenance time and money
252
Pros and cons of steam retort
Pros
Low capital investment
Easy to operate manually
Can process most canned products
Cons
Venting uses a lot of steam and is not an economical step
Uses a lot of energy
Inflexible
Cannot process most fragile containers such as pouches, plastic bottles and jars
253
Pasteurisation, aims, advantages and disadvantages
Aims
To kill pathogens, to reduce microbial load (food is not sterile) and to inactivate enzymes
Adv
Minimal damage to flavour, texture, nutritional quality
Disadvantage
Short shelf life
Another preservation method must be used like refrigeration or freezing
254
Appertisation, aims, advantages and disadvantages
Aims
To kill all bacteria able to grow in product
Food will be commercially sterile
Adv
Long shelf life
No other preservation method is necessary
Disadvantages
Food is over cooked
Major changes in texture, flavour and quality
255
Batch low temperature long time LTLT pasteurisation
63 degrees
30 minutes
Refrigerated
256
Flash high temperature short time HTST pasteurisation
72-74 degrees
15-20 seconds
Refrigerated
257
Extended shelf life ESL pasteurisation
Micro-filtration 90-110 degrees
4-6 seconds
Refrigerated
258
Ionising radiation, advantages and disadvantages
Permitted in over 60 countries
Irradiated foods must be labelled
Consumer resistance, used little in UK
Isotron, gamma producing plant, Sweden
Adv
At low levels <5 kGy virtually no sensory change
No non food residue in product
Negligible heat production
Instantaneous and uniform penetration
Disadvantages
Enzymes not inactivated
High doses produce chemical changes
Induction of harmful constituents in food
Safety precautions required in the processing facility
259
Refrigeration
Old method and still widely used today
Increasing use today - customer demand for high quality foods with shorter cook times
Little change in flavour, colour, taste, shape or texture
Foods stored between 0-5 degrees and above freezing point
Changes to flora to slow growing psychotrophs which eventually spoil food
Psychrotrophic pathogens can grow like: clostridium botulinum (non proteolytic), yersinia enterocolitica, l monocytogenes , pseudomonas and hyphomonas
Acidic proteins rise due to cold shock - ssDNA breaks, membrane stiffness
260
Heat induced chemical changes have much larger … than microorganisms
Z values
261
Diarrhoeal syndrome - bacillus cereus
10^5 - 10^7 infectious dose
Toxin produced in small intestine of host
Toxin: proteins, 3 components MW37, 38, 46kda
Inactivated at 56 degrees for 5 min
Unstable between ph <4 and >11
8-16hr incubation period
12-24hr duration of illness
Abdominal pain, watery diarrhoea and nausea
Caused by meat products, soups, vegetables, puddings, sauces, milk
262
Emetic syndrome - bacillus cereus
10^5-10^8 cells g-1 infectious dose
Toxin pre formed in foods
Toxin is a cyclic peptide, MW 1.2kda
Stable 126 degrees for 90 min
Stable at 2-11 ph
0.5-5hr incubation period
6-24 hr duration of illness
Nausea, vomiting, malaise, diarrhoea due to extra enterotoxin production
Furies and cooked rice, pasta, pastry and noodles
