Milk and Dairy Products

Question 1

1. What is organic milk?
2. What is Jersey and Guernsey milk
3. What is homogenised milk?
4. What is standardised milk?

Answer 1

1. Cows that have been grazed on pasture that had no chemical fertilisers, pesticides or agrochemicals
2. Produced from Jersey or guernsey breeds of cows
3. Forcing the milk at high pressure through small holes, breaking of fat blobules to spread it evenly and prevent a cream layer
4. Milk with the fat content adjusted to a specified value- full fat milk

Question 2

What are animal milk alternatives?

Answer 2

Colloidal suspensions or emulsions by milling:
* Cereal-based
* Legum based
* Nut-based
* Pseudocereals

Question 3

What are natural and foreign components of milk?

Answer 3

Natural
* Major- water, fat, protein, lactose
* Minor- salts, citric acid, enzymes, vitamins, gases, phospholipids, immunoglobulins

Foreign
* Antibiotics
* Herbicides
* Insecticides
* Non-original water
* Cleaning agents
* Disinfection

Question 4

Which milk contains higher calcium and lower levels of fat soluble vitamins?

Answer 4

Skimmed milk

Question 5

What pH range do the following products have?
1. Milk
2. Butter
3. Cheese

Answer 5

1. Milk- 6.4-6.8
2. Butter 6.1-6.4
3. Cheese 4.8-7.4

Question 6

What can cause a decrease or increase in pH?

Answer 6

Decrease
* Microorganisms if lactose fermenting
* Extensive lipolysis
* Increasing temperature
Increase
* Physiological stress
* Decreasing temperature

Question 7

What is the water activity of the following?
1. Whole milk
2. Bacteria
3. Yeast
4. Moulds

Answer 7

1. > 0.9
2. > 0.9-0.91
3. > 0.87-0.94
4. > 0.7-0.8

Question 8

What are the most important pathogens potentially found in milk, their contamination source and whether they can frow in the bulk tank

Answer 8

• Campylobacter jejuni- environment (faeces)- no
• Listeria monocytogenes- environment (feeds, faeces)- yes
• Mycobacterium paratuberculosis- environment- no
• Salmonella- environment- yes
• Staphylococcus- interior or teats- yes

Question 9

What are the most common spoilage organisms in milk, their contamination source, and whether it can grow in the bulk milk tank

What else can be a spoilage source of milk?

Answer 9

• Bacillus sporothermodurans- environment (feeds to faeces)- no
• Butyric acid bacteria- environment- no
• Pseudomonas- environment/milking equip- yes
• Streptococcus thermophilus- environment- yes

Chemical- oxidation of fat

Question 10

What pathogens potentially found in milk can exitibit a dual role of spoilage and pathogenic?

Answer 10

• Bacillus cereus (spores)- environment/milking equip- can grow in bulk tank
• E. coli- environment- yes

Question 11

1. What systemic infectious agents can be found in milk?
2. What contagious mastitis pathogens can be found in milk?
3. What environmental mastitis pathogens can be found in milk?

Answer 11

1. TB, Q-fever, Leptospirosis, Salmonellosis
2. Staph aureus, strep dysgalac/agalac, mycoplasma, corynebacterium bovis
3. Strep uberis, E colie, Klebsiella

Arcanobacterium pyogenes- summer mastitis

Question 12

What can allow the increase of infectious agents in dairy products?

Answer 12

• Milk with high load of bacteria
• Contamination of product
• Inadequate storage temperatures
• Inefficient/deficienct treatments

Question 13

What should the storage temperature of milk be on farm?

Answer 13

• <8 degrees if collected daily
• <6 degrees if not daily
• During transport <10 degrees
• No refrigeration if collection within 2 hours of milking

Question 14

Why should pregnant women avoid soft cheeses?

Answer 14

Listeria sp

Question 15

1. Who enforces milk nationally and locally?
2. Who checks milk residues
3. Who is responsbile for eradication programs?

Answer 15

1. FSA- nationally, Local- EHOs
2. VMD- residues
3. APHA- eradication programs

Question 16

What standards do the following types of milk need to meet?
1. Raw intended for consumption
2. Raw milk intended for direct consumption
3. At manufacture of dairy products before processing

Answer 16

1. Plate count <100,000, SCC < 400,000
2. Plate count <20,000, Coliforms <100
3. Raw- plate count <300,000, processed <100,000

Question 17

1. What is required to sell raw milk from a cow?
2. What is required to sell raw milk from sheep, goats and buffaloes?
3. What do both require?

Answer 17

Cow
* Herd tuberculosis free
* Health warning
* Inspections twice a year
* Samples and tested quarterly for TVC and coliforms

Sheep goats and buffaloes
* buffalo officially tuberculosis free
* health warning
* Inspections programmed on risk basis

Both
* May only be sold by registered milk production holdings
* Herd brucellosis free or officially brucellosis free
* Comply with hyigene rules
* Health warning

Question 18

Where is raw milk sale banned?

Answer 18

Northern Ireland and Scotland

Question 19

What is considered when deciding on a heat treatment?

Answer 19

Objective
* Intended shelf life
* To be refrigerated

Later step to reduce hazard
Physical and chemical feature of final product
* pH
* Viscosity
* Acid and anaerobiosis

Question 20

What is the D and Z value of the thermal death curve?

Answer 20

D value: heat resistance of organism- time @ given temperature required to reduce population by 1 log

Z value: temperature change required to alter D value by factor of 10

Question 21

What are the different techniques of pasturisation?

Answer 21

Low temp long time
* 63.5 degrees for 30 mins

High temperature short time
* >72 minimum of 15 seconds

Flash pasturisation
* 88 degrees for 1 second

Question 22

How is milk ‘sterilised’?

Answer 22

• No legally defined process
• Efficient against most heat resistant spores
• Pre-heated to 50 degrees followed by homogenisation
• FIlled air tight bottles through steam chamber 110-130 degrees for 10-30 minutes
• Keeps for 6 months without refrigeration- sweeter taste

Question 23

How is UHT milk treated?

Answer 23

> 135 degrees for 1 second
* Plus appropriate holding time to produce ‘commercial sterility;
* Opaque containers

Question 24

How is evaporated and condensed milk produced?

Answer 24

Evaporated
* Standardising, heat treatment and evaporating the milk under reduced pressure 60-65 degrees
* Homogenised to prevent seprating under storage
* Poured into cans and moved to a steriliser for 10 minutes
* Keeps 1 year without refrigeration

Condensed milk
* Standardised milk 110-115 degrees for 1-2 mins
* Milk homogenised, sugar added and evaporated 55-60 degrees
* Not sterilised, preserved by high surgar content
* Conc upto 3 times of original milk

Question 25

What are the different processes of filtered and dried milk?

Answer 25

Filtered * microfiltration, ultrafiltration and nanofiltration * Can extend shelf life and can last 1 week when opened Dried milk * Spray drying- concentrated milk into a hot air chamber- droplets lose their water and fall to floor as fine powder * Roller drying- concnetrated milk onto heated rollers, thin film of powder, scraped off

Question 26

1. What are the antimicrobial properties lactoferrin? 2. What is the activity following pastuization 3. What is the activity following UHT?

Answer 26

1. Iron binding protein; deprives Fe, Mg and Ca needed for microbial growth and survival 2. Similar 3. Denatured

Question 27

1. What effect on bacteria does lactoperoxidase have? 2. What properties does it have after pasturization 3. What effect does it have after UHT 4. Why can it be used to qualitate pasturization?

Answer 27

1. Bacteriostatic 2. 70% activity if not flash pasturised 3. Inactivated 4. If not detected temp must have been >78 for 15 seconds

Question 28

1. What are the antimicrobial properties of lysozyme? 2. What effect does pasturization have? 3. What effect does UHT have?

Answer 28

1. Bactericidal mainly against gram + bacteria 2. >75% activity retained at 80 degrees for 15 seconds 3. Inactivated

Question 29

1. What are the antimicrobial properties of xanthine oxidase? 2. What activity does it retain after pastrization? 3. What is the UHT effect?

Answer 29

1. Supplies lactoperoxidase with hydrogen peroxide 2. Retains activity at 73 degrees for 7 min or 80 for 50 seconds 3. Inactivated

Question 30

1. What are the function of bovine immunoglobulins 2. What is the effect of pasturization 3. What happens after UHT?

Answer 30

1. Transfers immunity against pathogens to calves 2. Retains full at 62.7 for 30 min, 59-76^ after HTST 3. Denatures

Question 31

What are the different Immunoglobulins in cows milk and what are there functions?

Answer 31

* IgG2 most important * IgM fixates the complement for opsonisation of pathogens, agglutinates, neutralises toxin * IgA agglutination of bacteria and neutralize toxins * IgG1 opsonisation of bacteria

Question 32

1. What are the antimicrobial properties of Nisin and Bacteriocins? 2. What is there activity after pasturization? 3. How does UHT affect it?

Answer 32

1. Antimicrobial peptides 2. Heat stable and retain activity after pasturization 3. Variable

Question 33

1. How are oligosaccharides, lipid fragments and protein fragments affected by pasturization and UHT? 2. What are the anitomicrobial properties of oligosaccharides and lipid fragments?

Answer 33

1. Oligosaccharides- heat stable, lipid fragments/protein- most likely no effect. UHT- no effect 2. Oligosaccharides- bind to pathogens to prevent adhesion of pathogens to intestinal epithelium Lipid- particularly gram + some antiviral activity

Question 34

1. What is the purpose of the resazurin test? 2. What is the purpose of a pH and alcohol test?

Answer 34

1. Oxidation-reduction indicator in cell viability assays for bacteria and mammalian cells- indicates contamination 2. Fermentation leats to alcohol and lactic acid

Question 35

What happens when milk is heated above 85 degrees in cheese processing?

Answer 35

* K-casein reacts with Beta lacto-globulin * Micelle becomes coarser and open spongy gel that absorbs liquid * Negatively charged K-casein taile sticking out prevents clumping * Fat incorpotated into mesh * Separation from the water soluble substances (whey)

Question 36

1. What causes sour or sweet curd formation of cheese? 2. How is curd processed? 3. How is cheese ripened?

Answer 36

1. Sour curd- fermentative bacteria (can add acid), Sweet- addition of rennin- 30/40 degrees 2. Salted, coloured, secondary bacteria, condensing/squeezing 3. Determines final texture and aroma- hard ripened/soft ripened

Question 37

What is the difference between soft and hard ripened cheese? Name examples of both

Answer 37

Hard- cheddar * further compression and wrapped in wax/plastic * Prevent contamination, loss of moisture * Incubated for bacteria Soft- camebert * A microbe on surface * protein-digesting enzyme: creamier

Question 38

1. What is cream? 2. What is yoghurt?

Answer 38

Cream is the separation of fat later in milk * Min 10% fat * Single cream 18% fat * Whipping 40% fat * Double 48% fat Yoghurt * Fermentation of milk by lactic acid forming bacteria * Lactobacillus and streptococcus

Question 39

What is butter and margarine?

Answer 39

Phase inversion: fat in water emulsion Churning: * ruptures fat membranes * join and form network with air bubbles * trapping of liquid * clumps increase in size * foam leaks- buttermilk Margarine * Hydrogenation of animal or vegetable oils

Question 40

What are the hazards to public health of cheese production?

Answer 40

* Sterility of raw product * Hygiene during processing * Heat treatment