Semester 1 Flashcards
What is not produced in mammary gland secretory cells but happens to be in these cells?
Immunoglobulins
Is the amount of milk regulated by microbes present in the mammary gland?
No
What biological molecule is not considered as a primary natural microbial system in milk?
Hypothiocyanite
Is heat treatment the critical step in maintaining the microbiological quality of milk?
True
Is streptococci the main bacterial group associated with cows mastitis?
True
What cfu / ml of PCA plates is considered as good in raw milk?
1000
What of the following preservation methods cause less nutritional damage to milk?
Pasteurisation
Honeybees poses microbes in their guts that are involved in honey fermentation
T or F
True
What part of the body do bees use to make royal jelly?
Head
What is the main microbiological concern with regards to the safety of honey?
Clostridium
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?
- 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
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?
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
What does oxidase positive mean?
Why don’t lactic acid bacteria have this oxidase?
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
What is a mesophilic lab?
Fermentation’s between 20 and 30 degrees
Cheese, fermented meats and veg eatables
Buttermilk
Sour cream
Diacetyl - cheesy, buttery
Eg. Lactococcus, leuconostoc
What is a thermophilic lab?
Fermentation’s between 35 and 42 degrees
Stirred or set yoghurts
Acetaldehyde - fruity, sweet
Eg. Lactobacillus, streptococcus
How are lactic acid bacteria preserved?
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
What are the bacteriocins? (LAB)
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
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?
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!
Why are fermented milk products made?
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)
What are probiotics?
Live microbes which when given in adequate amounts confer a health benefit on the host
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?
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
What are the microbial cultures used for making cheese?
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
What are the cheese production stages?
Pasteurisation
Addition of starter (ripening)
Addition of rennet (coagulation)
Settling of curd (pitching)
Separation of whey
Milling and salting
Pressing
Maturation (soft or hard)
What can spoil yoghurt and cheese?
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
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
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)
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
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
LAB are the … microbes involved in food fermentation’s
Most popular
LAB fermentation’s extend shelf life and improve … properties
Organoleptic
The … between L. Delbrueckii and S. thermophilus in milk results in yoghurt production
Mutualism
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
In beer, yeasts mainly Saccharomyces are responsible for alcoholic …
Fermentation
Yeast and LAB work in … in order to produce other alcoholic products such as wine, kefir and kumis
Symbiosis
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
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
Examples of biological hazards? (Bacteria, viruses, parasites)
Salmonella, Campylobacter, Norovirus, E.Coli, Clostridium
Examples of chemicals hazards
Naturally occurring chemicals - mycotoxins
Intentionally added chemicals - preservative sodium nitrate
Unintentionally added chemicals - pesticides
Examples of physical hazards
Insects, hair, metal, plastic, glass, dirt
What are the tasks involved in development of the HACCP plan?
- Assemble the HACCP team
- Describe the food and its distribution
- Describe the intended use and consumers of the food
- Develop a flow diagram which describes the process
- Verify the flow diagram
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
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
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
HACCP plan
HACCP team and assigned responsibilities
Description of food, it’s distribution, intended use and consumer
Verified flow diagram
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
What is the primary objective of heat treatment?
To improve safety (eliminate pathogens)
What is the secondary objective of heat treatment?
To extend shelf life (reduce load of spoilage organisms)
What are the types of heat treatment?
Blanching / cooking
Pasteurisation
Appertisation - retorting (canning), UHT / aseptic packaging
Who is pasteurisation named after?
Louis Pasteur
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)
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
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
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)
What is sterilisation?
Complete destruction of all microorganisms
Very harsh treatment, dramatic changes in food quality
Essential in clinical settings (surgery etc)
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)
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
General considerations for canning
Nature of food (ph, composition, viscosity(
Heat resistance of organisms
Storage conditions after thermal processing
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…
Spores are more heat resistant than…
Vegetative cells
Bacteria subjected to heat are killed at a rate that is .. to the number of organisms present
Proportional
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%!
What is an application of D values?
Allow accurate predictions of the rate of thermal lethality
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
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
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
How a particular microorganism responds to temperature is defined by 3 cardinal points
Minimum, optimum, maximum temps for 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 problematic in food
Below -10 degrees…
NO microbial growth can occur
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
Frozen foods < - 18 degrees
Maintains sensory and nutritional properties
Does not sterilise food
Dependant on both temp and aw
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)
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
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
What is irradiation?
Exposure of food to electromagnetic radiation to kill microorganisms
What is high hydrostatic pressure (pascalisation)
Exposure to high pressure (400-1200 Mpa) to kill microorganisms
What is pulsed high electric field treatment (PHEF)?
Inactivation of microorganisms after exposure to electric fields (15 kV /cm)
What is pulsed light?
Successive repetition of high power pulsed of broadband emission light
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)
What is cold plasma technology?
Inactivates target organisms by releasing the stored energy
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
Electromagnetic radiation used in food preservation:
Microwave
Ultraviolet
Ionising radiation
The higher the frequency the more energy the radiation contains
E = hv
H = planck’s constant
V = frequency of radiation
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
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
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)
Types of electromagnetic radiation used to preserve foods
Focused electron beam
X rays
Y (gamma rays)
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
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
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
Milk is the perfect environment for bacteria to …
Profilerate
Why are lactic acid bacteria abundant when there’s high lactose content?
They use it for fermentation / proliferation
Water buffalo have a very high fat content in their milk.
What is their milk used to make?
Mozzarella
How is milk produced?
Lactation
What is the udder?
What is the alveolus lined with?
A highly developed and modified sweat gland
Milk producing epithelial cells
What is meat comprised of?
Water - 75%
Protein - 19%
Fat - 2.5%
Carbohydrate - 1.2%
Inorganic compounds - 0.65%
Characteristics of meat
Most b vitamins in useful quantities
Water activity =0.99
Redox potential - mostly facultative anaerobic
Ph = 5.2 to 7
What is the production process of meat?
Farm > transport > lairage > slaughter > dressing > chilling > cutting and boning
What are the intrinsic bacteria that can contaminate meat?
Commensal bacteria naturally present in muscular tissues and blood vessels
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
Examples of facultative anaerobes that can contaminate meat?
LAB: natural gut micro flora - eg enterococcus, lactobacillus, pediococcus
Staphylococcus (hide)
Shewanella (poultry)
What are examples of aerobes that can contaminate meat?
Pseudomonas
Acinetobacter
Moraxella
Micrococcus
Fungi and yeast can also …the meat surface
Contaminate
How do carbohydrates lead to meat Spoilage?
Glycogen and glucose > CO2 > organic acids (lactic acid) > sour - cheesy by LAB
LAB
Enterobacteria
How do lipids contribute to meat spoilage?
Aldehydes and ketones > fruity sweet
LAB