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YEAR 2 - Food microbiology > Semester 1 > Flashcards

Semester 1 Flashcards

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1
Q

What is not produced in mammary gland secretory cells but happens to be in these cells?

A

Immunoglobulins

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2
Q

Is the amount of milk regulated by microbes present in the mammary gland?

A

No

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3
Q

What biological molecule is not considered as a primary natural microbial system in milk?

A

Hypothiocyanite

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4
Q

Is heat treatment the critical step in maintaining the microbiological quality of milk?

A

True

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5
Q

Is streptococci the main bacterial group associated with cows mastitis?

A

True

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6
Q

What cfu / ml of PCA plates is considered as good in raw milk?

A

1000

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7
Q

What of the following preservation methods cause less nutritional damage to milk?

A

Pasteurisation

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8
Q

Honeybees poses microbes in their guts that are involved in honey fermentation
T or F

A

True

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9
Q

What part of the body do bees use to make royal jelly?

A

Head

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10
Q

What is the main microbiological concern with regards to the safety of honey?

A

Clostridium

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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
  1. Preservation - extend shelf life vs raw material
  2. Perception - improved aroma and flavour characteristics
  3. Nutrition - increased vitamin content and digestibility
  4. Removal of toxic or allergic compounds - cassava, milk
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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

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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

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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

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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

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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

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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

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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!

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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)

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20
Q

What are probiotics?

A

Live microbes which when given in adequate amounts confer a health benefit on the host

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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

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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

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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)

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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

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25
Q

What are the essential ingredients of beer?

A

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

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26
Q

What are the brewing steps?

A

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)

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27
Q

What happens during the Malting brewing step?

A

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

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28
Q

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?

A

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

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29
Q

LAB are the … microbes involved in food fermentation’s

A

Most popular

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30
Q

LAB fermentation’s extend shelf life and improve … properties

A

Organoleptic

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31
Q

The … between L. Delbrueckii and S. thermophilus in milk results in yoghurt production

A

Mutualism

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32
Q

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

A

Starters
Later on

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33
Q

In beer, yeasts mainly Saccharomyces are responsible for alcoholic …

A

Fermentation

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34
Q

Yeast and LAB work in … in order to produce other alcoholic products such as wine, kefir and kumis

A

Symbiosis

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35
Q

What is HACCP?

A

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

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36
Q

Why is HACCP important?

A

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

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37
Q

Examples of biological hazards? (Bacteria, viruses, parasites)

A

Salmonella, Campylobacter, Norovirus, E.Coli, Clostridium

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38
Q

Examples of chemicals hazards

A

Naturally occurring chemicals - mycotoxins
Intentionally added chemicals - preservative sodium nitrate
Unintentionally added chemicals - pesticides

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39
Q

Examples of physical hazards

A

Insects, hair, metal, plastic, glass, dirt

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40
Q

What are the tasks involved in development of the HACCP plan?

A
  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
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41
Q

What are the 7 principles of HACCP implementation?

A

Hazard analysis
Determine the critical control points CCP
Establish critical limits
Critical control point CCP monitoring
Corrective actions
Establish verification procedures
Record keeping procedures

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42
Q

What is a critical limit?

A

A maximum / minimum value where a parameter must be controlled at a CCP to prevent the occurrence of a food safety hazard

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43
Q

When there is deviation from critical limits, corrective actions are taken to:

A

Determine and correct the cause of non compliance

Determine the disposition of non compliant product

Record the corrective actions that have been taken

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44
Q

HACCP plan

A

HACCP team and assigned responsibilities
Description of food, it’s distribution, intended use and consumer
Verified flow diagram

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45
Q

What is thermal processing of food?

A

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

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46
Q

What is the primary objective of heat treatment?

A

To improve safety (eliminate pathogens)

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47
Q

What is the secondary objective of heat treatment?

A

To extend shelf life (reduce load of spoilage organisms)

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48
Q

What are the types of heat treatment?

A

Blanching / cooking

Pasteurisation

Appertisation - retorting (canning), UHT / aseptic packaging

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49
Q

Who is pasteurisation named after?

A

Louis Pasteur

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50
Q

What is pasteurisation?

A

Aims to kill pathogens and to extend shelf life by reducing microbial load

Heat usually below 100 degrees and additional preservation needed (chilling)

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51
Q

What is appertisation and who is it named after?

A

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

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52
Q

What is the aim of appertisation?

A

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

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53
Q

What are the types of appertisation?

A

Ultra high temperature (UHT) 135 degrees for 1s in aseptic package (ambient)

Canning 115 degrees for 25-100 mins in cans /jars (ambient)

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54
Q

What is sterilisation?

A

Complete destruction of all microorganisms

Very harsh treatment, dramatic changes in food quality

Essential in clinical settings (surgery etc)

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55
Q

Methods for packaging thermally processed foods

A

In package sterilised products (cans, bottled products)

UHT or aseptically processed products (long life milk, fruit juices and soups)

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56
Q

What are the 4 steam based processes used in sterilising food?

A

Saturated steam - direct steam heating

Water immersion - indirect steam heating

Water spray - indirect steam heating

Steam air - direct steam heating

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57
Q

General considerations for canning

A

Nature of food (ph, composition, viscosity(

Heat resistance of organisms

Storage conditions after thermal processing

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58
Q

Kinetics of thermal killing

A

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…

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59
Q

Spores are more heat resistant than…

A

Vegetative cells

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60
Q

Bacteria subjected to heat are killed at a rate that is .. to the number of organisms present

A

Proportional

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61
Q

What is the D value?

A

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%!

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62
Q

What is an application of D values?

A

Allow accurate predictions of the rate of thermal lethality

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63
Q

What is the Z value?

A

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

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64
Q

What does the z value reflect?

A

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

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65
Q

What is the F value?

A

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

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66
Q

How a particular microorganism responds to temperature is defined by 3 cardinal points

A

Minimum, optimum, maximum temps for growth

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67
Q

Microbial growth occurs from -8 to over 100 degrees but:

A

Some organisms have specific temp requirements within this range

Food is only stored at certain temps

Mesophiles and pyschrotrophs are problematic in food

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68
Q

Below -10 degrees…

A

NO microbial growth can occur

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69
Q

Chilled foods 0-5 degrees

A

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

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70
Q

Frozen foods < - 18 degrees

A

Maintains sensory and nutritional properties

Does not sterilise food

Dependant on both temp and aw

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71
Q

Refrigeration

A

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)

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72
Q

Freezing

A

-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

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73
Q

What is Non thermal preservation methods (new developments)?

A

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

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74
Q

What is irradiation?

A

Exposure of food to electromagnetic radiation to kill microorganisms

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75
Q

What is high hydrostatic pressure (pascalisation)

A

Exposure to high pressure (400-1200 Mpa) to kill microorganisms

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76
Q

What is pulsed high electric field treatment (PHEF)?

A

Inactivation of microorganisms after exposure to electric fields (15 kV /cm)

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77
Q

What is pulsed light?

A

Successive repetition of high power pulsed of broadband emission light

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78
Q

What is ultrasound?

A

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)

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79
Q

What is cold plasma technology?

A

Inactivates target organisms by releasing the stored energy

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80
Q

What is high pressure processing (HPP)?

A

Cold pasteurisation of already sealed products

Introduced into a vessel under high hydrostatic pressure (200- 800 MPa) transmitted by water to kill microorganisms

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81
Q

Electromagnetic radiation used in food preservation:

A

Microwave

Ultraviolet

Ionising radiation

The higher the frequency the more energy the radiation contains

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82
Q

E = hv

A

H = planck’s constant

V = frequency of radiation

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83
Q

Preservation by exposure to microwaves

A

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

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84
Q

Preservation by exposure to UV light

A

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

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85
Q

Preservation by exposure to ionising radiation

A

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)

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86
Q

Types of electromagnetic radiation used to preserve foods

A

Focused electron beam

X rays

Y (gamma rays)

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87
Q

What is gamma irradiation?

A

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

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88
Q

What is electron beam irradiation (EBI)?

A

Uses low dose ionising radiation in crops or food to eliminate microbial contamination

Low cost, environment friendly, time effective

Extends shelf life

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89
Q

Electron beam irradiation

A

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

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90
Q

Milk is the perfect environment for bacteria to …

A

Profilerate

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91
Q

Why are lactic acid bacteria abundant when there’s high lactose content?

A

They use it for fermentation / proliferation

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92
Q

Water buffalo have a very high fat content in their milk.
What is their milk used to make?

A

Mozzarella

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93
Q

How is milk produced?

A

Lactation

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94
Q

What is the udder?

What is the alveolus lined with?

A

A highly developed and modified sweat gland

Milk producing epithelial cells

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95
Q

What is meat comprised of?

A

Water - 75%
Protein - 19%
Fat - 2.5%
Carbohydrate - 1.2%
Inorganic compounds - 0.65%

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96
Q

Characteristics of meat

A

Most b vitamins in useful quantities

Water activity =0.99

Redox potential - mostly facultative anaerobic

Ph = 5.2 to 7

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97
Q

What is the production process of meat?

A

Farm > transport > lairage > slaughter > dressing > chilling > cutting and boning

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98
Q

What are the intrinsic bacteria that can contaminate meat?

A

Commensal bacteria naturally present in muscular tissues and blood vessels

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99
Q

What are the extrinsic bacteria that can contaminate meat?

  • spoilage or pathogenic bacteria that contaminate meat during slaughter, processing and storage
A

Faeces
Hide contact
Spilling of bodily fluids
Aerosols or sprays
Contaminated hands or equipment
Abattoir workers
Inappropriate preservation methods

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100
Q

Examples of facultative anaerobes that can contaminate meat?

A

LAB: natural gut micro flora - eg enterococcus, lactobacillus, pediococcus

Staphylococcus (hide)

Shewanella (poultry)

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101
Q

What are examples of aerobes that can contaminate meat?

A

Pseudomonas

Acinetobacter

Moraxella

Micrococcus

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102
Q

Fungi and yeast can also …the meat surface

A

Contaminate

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103
Q

How do carbohydrates lead to meat Spoilage?

A

Glycogen and glucose > CO2 > organic acids (lactic acid) > sour - cheesy by LAB

LAB
Enterobacteria

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104
Q

How do lipids contribute to meat spoilage?

A

Aldehydes and ketones > fruity sweet

LAB

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105
Q

How do proteins contribute to meat spoilage?

A

Collagen, actin, myosin, myoglobin > short peptides, amino acids, amines (bitter putrid) > production of extracellular polysaccharides EPS = slime

Gram negative aerobes
Pseudomonas

106
Q

What bacteria does raw fresh meat contain?

A

Campylobacter
Salmonella
E. coli

107
Q

How can meat be preserved ?

A

Cured meats (LAB)
Fermented meats (LAB)
Aerobic chill storage
Vacuum packing
Modified atmosphere packing
Canning (clostridia)
Freezing

108
Q

What are the meat borne pathogens and where are they found?

A

Salmonella species - pork and chicken

E. coli O157:H7 - beef

C jejuni - chicken

L monocytogenes - environment

C botulinum - canned meats

109
Q

What is the FSA meat hygiene service and what does it include?

A

Responsible for providing verification and inspection in approved slaughterhouses

Animal welfare at slaughter, animal identification

110
Q

What is the trend of bacterial counts from fish?

A

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
Q

What bacteria are found in fish?

A

Most are gram negatives

Eg pseudomonas, acinetobacter, aeromonas, shewanella, vibrio, flavobacterium and cytophaga

112
Q

Spoilage of fresh fish vs fresh meat

A

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
Q

How does indole production spoil fish?

A

Spoilage bacteria convert tryptophan into indole which has intense faecal odour!

114
Q

How does formation of ammonia spoil fish?

A

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
Q

How does the formation of TMA spoil fish?

A

Spoilage bacteria convert trimethylamine N oxide TMAO and odourless osmolyte into the foul smelling trimethylamine

116
Q

Examples of fish borne disease

A

Vibrio cholerae

Vibrio parahaemolyticus

Vibrio vulnificus

Enteric viruses (Noro virus)

117
Q

What is scombroid fish poisoning?

A

If fish is not chilled properly after being caught, bacteria begin to convert histidine into histamine

118
Q

What is shellfish poisoning?

A

Bivalve molluscs are filter feeders and therefore accumulate toxins produced

119
Q

What is milk?

A

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
Q

What is the composition of milk?

A

Water - 87%
Protein - 3.5%
Fat - 4%
Lactose - 4.7%
Minerals - 0.8%

Water activity = 0.99
Ph = 6.4-6.6

121
Q

Steps of milk formation

A

Solution with lactose dissolved in water

Emulsion of spherical fat droplets

Suspension of Casein micelles

122
Q

How is milk produced via lactation?

A

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
Q

How is milk formed?

A

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
Q

How do bacteria get from the cows gut to the newborn?

A

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
Q

What are the natural milk antimicrobial systems?

A

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
Q

Milk distribution:
Historically vs Now

A

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
Q

What are the steps in milk production?

A

Milk production > milk collection > milk chilling and storage > milk packaging (heat treatment) > transport > consumer practices

PREVENT MASTITIS and microbial hazards

128
Q

Important risk factors in milk production

A

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
Q

What is inflammation of the mammary glands due to?

A

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
Q

How to prevent infections of the mammary gland?

A

Provision of clean litter
Rapid removal of slurry
Shave udders, trim tails
Wash teats with disinfectant
Keep parlour floor clean
Clean teat cups

131
Q

Mastitis detection - what are the main indicators of milk quality?

A

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
Q

Raw milk contains potentially many pathogens of significant concern.
What are the spoilage organisms?

A

Psychotrophs: pseudomonas, flavobacterium, alcaligenes
Some coli forms

133
Q

Pasteurised milk contains usually few pathogens of low concern.
What are the spoilage organisms?

A

Psychrotrophs
Spore forming pschrotrophs
Bacillus spp

134
Q

What can cause spoilage in the carbohydrates, proteins and lipids that make up milk?

A

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
Q

What may refrigerated raw milk contain that could compromise the quality of dairy products during storage?

A

May contain psychotropic bacteria that produce thermoresistant exo proteases and lipases which can compromise quality

136
Q

Microbial hazards in milk today

A

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
Q

What pathogens could be found in raw milk?

A

L monocytogenes

Salmonella

E. coli

138
Q

Milk can only come from herds that officially … and … free

A

TB

Brucellosis

139
Q

What is honey?

A

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
Q

Process of honey production by the bee

A

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
Q

How is bee pollen produced?

A

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
Q

How is royal jelly produced?

A

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
Q

How is beeswax produced?

A

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
Q

The preservation of honey

A

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
Q

Microbes of concern in honey

A

Come from post harvest handling:

Yeasts, spore forming bacteria, coli forms and clostridia

146
Q

Primary sources of microbial contamination in honey

A

The microbiota of honeybee products, dust, air, food handlers, cross contamination, equipment

147
Q

Why is honey suitable for long term storage?

A

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
Q

Fermented foods

A

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
Q

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 digest ability

150
Q

What gram positive bacteria are produced from the glycolysis pathway?

A

Lactobacillus
Lactococcus
Pediococcus
Enterococcus
Vagococcus
Streptococccus

151
Q

What gram positive bacteria are produced from the 6 P-gluconate pathway?

A

Carnobacterium
Leuconostoc
Oneococcus
Weisella
Lactosphaera

152
Q

What does the F ATPase of LAB do?

A

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
Q

Yoghurt: milk fermented by LAB

A

Easy to produce and generally safe > only contamination with fungi and yeasts

Extends shelf life due to anti microbial properties of LAB

154
Q

What is the heat treat step in yoghurt production?

A

80-85 degrees for 30 min / 90-95 degrees for 5-10 min

Reduces bacterial load
Improved as growth medium
Starts casein denaturation

155
Q

What is the starter in milk production?

A

Lactobacillus delbrueckii and streptococcus thermophilus

Added in equal numbers
Produce 1% lactic acid, ph 4.2-4.3

156
Q

Incubation step of milk production - 42 degrees

A

Addition of probiotics

Lactobacillus casei and bifidobacterium

157
Q

Whole hops are added to sweet wort and boiled in the copper to…

A

Extract bitterness, flavour and aroma from the hops
Inactivates enzymes
Pasteurises wort
Concentrates wort

158
Q

What does Oenococcus do to wine?

A

Reduced acidity

Increased body - dextrans and glucans (EPS)

Increased flavour complexity - buttery, nutty

159
Q

What are the kombucha fermentation steps?

A
  1. Glucose > ethanol catalysed by saccharomyces cerevisiae
  2. Ethanol > acetic acid catalysed by acetobacter aceti
160
Q

Ale yeast fermentation

a- galactosidase

A

Saccharomyces cerevisiae

Growth 5-40 degrees

Fermentation 12-18 degrees

Top fermenting

Melibiose negative (remains)

161
Q

Lager yeast fermentation

a- galactosidase

A

S carlsbergensis and s pastorianus

Growth 0-33 degrees

Fermentation 8-12 degrees

Bottom fermenting

Melibiose positive (disappears)

162
Q

Listeria monocytogenes

A

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
Q

Listeria monocytogenes infections

A

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
Q

Clinical features of Listeria monocytogenes infection

A

CNS disease (tropism for brain tumour) - meningitis, meningocencephalitis, brain abscesses

Sepsis (most common in compromised hosts)

Endocarditis

Gastroenteritis

Focal infections

Hepatitis

Myocarditis

165
Q

Pathogenesis of listeria monocytogenes infection

A

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
Q

Escherichia coli

A

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
Q

E. coli infections

A

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
Q

Association with E. coli and foods

A

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
Q

E coli

A

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
Q

What is sensitivity?

A

Probability of diseased patients (based on gold standard) having a positive result when tested by diagnostic test

171
Q

What is specificity?

A

Probability of NON diseased patients (based on gold standard) having a negative result when tested by diagnostic test

172
Q

Staphylococcus aureus

A

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
Q

Staphylococcus aureus infections

A

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
Q

Clinical decay ties of staph aureus infection

A

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
Q

Pathogenesis of staph aureus infections

A

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
Q

Association with staph aureus and food

A

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

177
Q

Bacillus cereus

A

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

178
Q

Bacillus cereus infections

A

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
Q

Diarrhoeal syndrome of bacillus cereus infection

A

Haemolytic enterotoxin HBL (proteins B, L1 and L2), a non haemolytic enterotoxin NHE and cytotoxin K produced by about 40% of strains

180
Q

Emetic syndrome of bacillus cereus infections

A

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
Q

Association with bacillus cereus and food

A

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
Q

Clostridium botulinum

A

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
Q

Clostridium botulinum

A

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
Q

Clostridium botulinum infections

A

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
Q

Pathogenesis of clostridium botulinum infections

A

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
Q

Association with clostridium botulinum and food

A

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
Q

Viral foodborne diseases

A

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

188
Q

Norovirus

A

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
Q

Mycotoxins

A

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
Q

ETEC E. coli

A

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
Q

EIEC E. coli

A

Invades and multiplies within colon epithelial cells (ulceration, inflammation)

192
Q

EPEC E. coli

A

Adhere to enterocyte membrane producing attaching and effacing lesions

193
Q

EHEC - E. coli O157:H7

A

Cytotoxins (verotoxin) VTI and VTII (shiga toxin)

194
Q

Food borne and waterborne diseases worldwide

A

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

195
Q

Foodborne diseases

A

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
Q

Chemical agents of food borne disease

A

Heavy metals - lead, cadmium and mercury

Persistent organic pollutants - polychlorinated biphenyls and dioxins

Naturally occurring toxins - mycotoxins, marine bio toxins

197
Q

Parasites - agents of foodborne disease

A

Animal or fish parasites - cryptosporidium Parvum, giardia lamblia

198
Q

Micro organisms - agents of foodborne disease

A

Bacteria - most frequent cause

Viruses - hepatitis A/E, norovirus, norlwalk

Fungi - aflatoxins

Prions - BSE or mad cow disease , vCJD in humans

199
Q

Modes of bacterial food poisoning

A

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

200
Q

Clostridium perfringens

A

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
Q

Clostridium perfringens food borne illness

A

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
Q

Campylobacter

A

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
Q

Campylobacter as foodborne pathogen

A

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
Q

Campylobacter epidemiology in UK

A

Highest in west and north - males more cases than females

Highest in children <5 years

Higher in rural areas with agricultural activity

205
Q

Dioxin crisis to determine poultry related campylobacter enteritis

A

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
Q

Salmonella

A

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

207
Q

The global burden of salmonella

A

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

208
Q

Diseases caused by salmonella

A

Typhoid fever

Enteric fever

Enteritis

Bacteremia

Asymptomatic carriage

209
Q

Reptiles as a vector for salmonella

A

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

210
Q

What does the growth / survival of food micro flora depend on?

A

Properties of food

Processing

Storage conditions

Properties of organisms

211
Q

Impact and significance of food microflora

A

Food spoilage (undesirable)

Foodborne illness (undesirable)

Fermentation (desirable if purposeful) - improved acceptability, nutrition, preservation

212
Q

Agents of foodborne illness (food safety)

A

Cause food borne illness

Food is a vector

Limited number of types

Low numbers can cause illness (some <10)

213
Q

Agents of spoilage (food spoilage)

A

Cause undesirable changes in quality

Changes caused by growth / enzymes

Numerous types cause spoilage

High numbers required (~10^7)

214
Q

What are the 4 factors that affect microbial growth?

A

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

215
Q

Milk spoilage as an example of the complex process of spoilage

A

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
Q

The effect of ph on microbial growth

Ph = -log10 [H+]

A

[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
Q

Optimum growth ph for some microorganisms

A

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
Q

Mechanisms for responding to low ph stress in microbes

A

H+ consumption

Urea production

Removal of H+ (using ATP)

219
Q

Microbial inhibition by weak organic acid

A

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
Q

The effect of redox potential Eh on microbial growth

A

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
Q

The effect of redox potential Eh on microbial growth

A

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
Q

The effect of water activity aw on microbial growth

Aw = p divided by p0

A

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
Q

Even if no microbial growth is possible in lower aw ranges, food spoilage is still …

A

Possible

224
Q

Resistant biological structures

A

Egg shells

Nut cases

Skins

Hides

225
Q

Natural anti microbial systems

A

Coumarins - fruits and vegetables

Lysozyme (also in saliva) - cows milk and eggs

Essential oils - herbs and spices

Allicin - garlic

226
Q

The effect of temp on microbial growth

A

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
Q

The effect of temp on microbial growth

A

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
Q

Why is it important that freezers are lower than -5 degrees?

A

Because psychrotophs (facultative for cold) can still grow at this temp

Their minimum temp range is -5 to 5 degrees

229
Q

Effect of temp on microbial growth

A

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
Q

Relative humidity

A

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
Q

Gaseous atmosphere

A

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
Q

The effect of implicit factors on microbial growth

A

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
Q

The effect of processing factors on microbial growth

A

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
Q

The effect of implicit factors on microbial growth

A

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
Q

Chemical preservatives

A

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
Q

Nitrite food preservation

A

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
Q

Sulphites food preservation

So2, h2s, na2s2o5

A

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
Q

Antibiotics food preservation

A

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
Q

Acids food preservation

A

Benzoic, sorbic, propionic acid and parabens

240
Q

Food preservation by the use of reduced temp

A

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
Q

Food preservation by modified atmosphere packaging

A

With specialised packing material, the atmosphere around a food can be modified to inhibit microbial growth

242
Q

Vacuum packing - product packed in a vacuum

A

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
Q

Modified atmosphere packing MAP

A

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
Q

Controlled atmosphere packing CAP

A

Tailored atmospheres which are maintained (steady state)

Used for bulk storage / transport

245
Q

Hurdle technology

A

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
Q

High acid food (ph <3.7) considerations when canning

A

Surviving spore forming bacteria will NOT grow

Process relies on inactivation of Yeasts and moulds / maintenance of anaerobic conditions

Low temperature time combinations

247
Q

Acid foods (3.6<ph<4.5) considerations for canning

A

Process needs to eliminate spores of Bacillus coagulans, b thermoacidurans, b polymyxa which will outgrow if present

248
Q

Low acid foods (ph >4.5) considerations for canning

A

It they survive, spores of clostridium botulinum can grow and conditions will be ideal for growth and toxin production

High temp time combinations

249
Q

Pros and cons of steam air retort

A

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
Q

Pros and cons of water spray retort

A

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
Q

Pros and cons of water immersion retort

A

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
Q

Pros and cons of steam retort

A

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
Q

Pasteurisation, aims, advantages and disadvantages

A

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
Q

Appertisation, aims, advantages and disadvantages

A

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
Q

Batch low temperature long time LTLT pasteurisation

A

63 degrees

30 minutes

Refrigerated

256
Q

Flash high temperature short time HTST pasteurisation

A

72-74 degrees

15-20 seconds

Refrigerated

257
Q

Extended shelf life ESL pasteurisation

A

Micro-filtration 90-110 degrees

4-6 seconds

Refrigerated

258
Q

Ionising radiation, advantages and disadvantages

A

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
Q

Refrigeration

A

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
Q

Heat induced chemical changes have much larger … than microorganisms

A

Z values

261
Q

Diarrhoeal syndrome - bacillus cereus

A

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
Q

Emetic syndrome - bacillus cereus

A

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

YEAR 2 - Food microbiology (1 decks)

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