Milk and Dairy Products

Question 1

What products are made from raw milk?

Answer 1

1. Liquid Milk
   - Raw bottled
   - Pasteurized
   - UHT
   - Sterilised
2. Fermented Milk
   - Hard Cheese
   - Soft Cheese
   - Yogurt
   - Buttermilk
3. Butter
4. Cream and milk based desserts
   - Fresh
   - UHT
   - Sterilised
5. Concentrated milk (Dried)
6. Ice cream

Question 2

What is organic milk?

Answer 2

From cows that have been grazed on pasture that had no chemical fertilisers, pesticides or agrochemicals

Question 3

What is homogenised milk?

Answer 3

Forcing the milk at high pressure through small holes, breaking of fat globules to spread it evenly and prevent a creamy layer.
Most frequently available

Question 4

What is standardised milk?

Answer 4

Milk with the fat content adjusted to a specified value. Ex. Full fat milk

Question 5

What are the two ways of milk production by the epithelial cells of alveoli?

Answer 5

Synthesis: milk fat, most of the protein components and lactose
Diffusion: water, minerals and vitamins

Question 6

What are the 4 major components of milk?

Answer 6

Water
Fat
Protein
Lactose

Question 7

What are the minor components of milk?

Answer 7

Salts, Citric acid, Enzymes, Vitamins, Gases, Phospholipids, Immunoglobulins

Question 8

What are some foreign components found in milk?

Answer 8

Antibiotics
Herbicides, Insecticides
Non-original water
Cleaning agents
Disinfection agents/residues
Infectious agents?? and enzymes synthetised by these

Question 9

Describe the main characteristics of skimmed milk

Answer 9

0.1-0.3% fat
- contains slightly more calcium than whole milk and lower levels of fat soluble vitamins (vitamin A)

Question 10

Describe the main characteristics of 1% fat milk

Answer 10

Contain 40% less total and saturated fat than semi-skimmed milk
Slightly lower levels of vitamin E and A
Higher calcium

Question 11

What is the fat % of semi-skimmed milk?

Answer 11

1.5-1.8

Question 12

What of the fat % of whole milk?

Answer 12

3.5-4.5

Question 13

What is the pH of milk?

Answer 13

6.4-6.8

Question 14

What causes the pH of milk products to decrease?

Answer 14

Microorganisms if lactose fermenting
Extensive lipolysis
Increasing temperature

Question 15

What causes the pH of milk products to increase?

Answer 15

Physiological stress
Decreasing temperature

Question 16

Name 4 systemic infectious agents found in dairy products

Answer 16

TB
Q-fever
Leptospirosis
Salmonellosis

Question 17

Describe the legal storage temperatures required for milk

Answer 17

<8°C if collected daily
<6°C if not daily collection
During transport- <10°C
No refrigeration if collection within 2 hrs of milking
At home ideally: 3C to 5 C

Question 18

Name 4 contagious mastitis pathogens spread during milking

Answer 18

Staphylococcus aureus
Streptococcus dysgalactiae
Mycoplasma spp
Corynebacterium bovis

Question 19

Name 3 environmental mastitis pathogens

Answer 19

Streptococcus uberis
E.coli
Klebsiella spp

Question 20

Name 2 mastitis pathogens seen in the summer months

Answer 20

Hydrotaea irritans
Arcanobacterium pyogenes

Question 21

What is the main reason pregnant women are told to avoid non pasteurised dairy products?

Answer 21

Listeria spp

Question 22

Which enforcement authority enforces hygiene on farm?

Answer 22

FSA - dairy hygiene inspector

Question 23

Which enforcement authority enforces hygiene on dairy plants and retailers?

Answer 23

Local authorities

Question 24

Raw cow’s milk intended for consumption must what standards?

Answer 24

Plate count (TVC) @ 30 °C: ≤ 100 000cfu/ml
Somatic cell count (SCC): ≤ 400 000 cfu/ml

Question 25

Raw cow's milk intended for direct human consumption must what standards?

Answer 25

Plate count (TVC) @ 30 °C: cfu/ml ≤ 20 000 Coliforms: <100cfu/ml

Question 26

What chemical and physical features of milk are assessed following heat treatment

Answer 26

pH Viscosity: slowest heating part Acid & anaerobiosis: spores of Clostridium botulinum

Question 27

Pasteurisation works against which pathogen?

Answer 27

Coxiella burnetti

Question 28

Describe the 3 pasteurisation methods

Answer 28

1. Low Temperature Long Time - LTLT ”holding method”: 63.5°C for 30 min 2. High Temperature Short Time (HTST)>72°C minimum 15 sec (recommended by ACMSF: 25 sec) 3. 88°C for 1 sec - Flash pasteurization

Question 29

Describe the features of sterilisation

Answer 29

- No legally defined process - Efficient against most heat resistant spores - Pre-heated ~ 50oC followed by homogenisation - Filled airtight bottles through steam chamber at 110-130ºC for 10-30 minutes. - Keeps for ~ 6 months without refrigeration. If opened ~ 5 days - Sweeter taste

Question 30

Describe UHT

Answer 30

Small milk pots in shops, hotels, planes, etc - 135 °C for 1 sec - Plus appropriate holding time to produce ‘commercial sterility’ - Opaque containers

Question 31

Name the two tests used to assess pasteurisation

Answer 31

Phosphate test - used to assess if pasteurisation has happened Peroxidase test - to see if it has been over heated – quality control rather than safety

Question 32

Describe the main features of evaporated milk

Answer 32

- Standardising, heat treatment and evaporating the milk under reduced pressure (60°C - 65°C) - Homogenised to prevent it separating under storage - Poured into cans and moved to a steriliser for 10 minutes - Keep ~ 1 year without refrigeration

Question 33

Describe the main features of condensed milk

Answer 33

- Standardised milk @ 110-115°C for 1-2 min - Milk homogenised, sugar added and evaporated (55-60ºC). - Not sterilised, preserved by the high sugar content - Concentration up to 3 times that of the original milk.

Question 34

Describe the main features of filtered milk

Answer 34

Microfiltration, ultrafiltration and nanofiltration Can extend shelf life up to 45 days when stored @ < 7°C and ~7 days once opened.

Question 35

Describe lactoferrin and an antimicrobial component of milk

Answer 35

Iron-binding protein; deprives Fe, Mg and Ca needed for microbial growth and survival, having bacteriostatic effects Similar activity pre and post pasteurization UHT effect = denatured

Question 36

Describe lactoperoxidase and an antimicrobial component of milk

Answer 36

Bacteriostatic 70% of activity @ 72o C for 15 s, Destroyed @>78°C for 15 sec If not detected: >>T in pasteurization - qualitative test UHT effect = inactivated

Question 37

Describe lysozyme and an antimicrobial component of milk

Answer 37

Bactericidal mainly against Gram + bacteria; >75% activity retained @ 80oC for 15 s UHT effect = inactivated

Question 38

Describe the resazurin test

Answer 38

Oxidation-reduction indicator in cell viability assays for bacteria and mammalian cells Indicates contamination

Question 39

The singlepath test is used for which microbe?

Answer 39

Listeria

Question 40

Which bacteria are involved in the fermentation of yogurt?

Answer 40

Lactobacillus and Streptoccoccus

Question 41

Describe butter making

Answer 41

Phase inversion: fat-in-water emulsion (milk) into water-in-fat emulsion

Question 42

Describe the main features of margarine

Answer 42

Not a dairy product Hydrogenation of animal or vegetable oils to give the desired texture Bubbling hydrogen through the oil at high temperature in the presence of a metal catalyst Saturation of carbon-carbon bonds in previously unsaturated fats