DAIRY Flashcards
1
Q
What breed of cow is most commonly used for milk production in Australia?
A
Friesians
2
Q
Why is milk considered ‘natures perfect food’?
A
It is produced to supply the neonate with complete nutritional requirements and so contains carbohydrates, lipids, proteins and salts
3
Q
Where is milk synthesised?
A
In the mammary gland of a mammal
4
Q
What is a singular milk producing unit called and describe its structure
A
An alveolus is a singular milk producing unit within the mammary gland
It consists of secretary cells surrounded by blood vessels
5
Q
What is the average composition of milk?
A
87% water
4% fat
9% non-fat milk solids (SNF)
6
Q
What factors can effect the composition of milk?
A
Nutritional Factors:
- type and availability of feed
Non-Nutritional Factors:
- breed
- stage of lactation
- season and temperature
- age and size of cow
- disease
- milking frequency
7
Q
What is colostrum?
A
The milk produced by the cow in the first 72 hours of lactation
It differs from regular milk in colour and composition
- yellowish in colour
- very high in salt
- very high in proteins + antibodies
8
Q
What effects can the composition of milk have on the end product?
A
- The physio-chemical properties
- Functional properties
- Pricing (price is based on milkfat/SNFs)
9
Q
What are the physical properties of milk?
A
- white
- opaque
- higher density than water
- lower freezing point
- pH from 6.6-6.8
- isotonic with cells
10
Q
Explain how fat exists in milk?
A
Milk is an oil in water emulsion and fat exists in globules dispersed throughout the milk
Eat fat globule is has a globule membrane which acts as an emulsifier
11
Q
What is the main type of lipid in milk?
A
Triglycerides are the primary type
15 fatty acids make up 95% of the TAG present
Most of these are saturated and contain an even no of carbons
C16 and C18 are most abundant
12
Q
Which triglyceride is exclusive to milk? What properties does this have?
A
C4
Gives buttery taste
Has a high melting point
13
Q
Explain the positioning of fatty acids in a triglyceride
A
Positioning is not random. The positioning of certain fatty acids affects crystallisation and behaviour of the milk fat
C4 and C6 are mostly in the -3 position
C18 is mostly in the -1 position
14
Q
Explain milk fat globule membrane
A
Membrane covers milk fat and acts as an emulsifier and to protect the fat from lipase
Originates from the plasma membrane of mammary secretory cells
Reddish/brown in colour due to xanthine oxidase enzyme
15
Q
What are the minor lipid components of milk fat globules?
A
Sterols - 95% are cholesterol Carotenoids - in trace amounts in core of globule - 95% beta carotene Fat soluble vitamins - A, D, E, K
16
Q
What are the 4 major types of caseins?
A
- alpha S1
- alpha S2
- beta
- kappa
17
Q
What are casein micelles
A
Contain 95% of casein in milk
Consist of 94% protein, 6% colloidal calcium phosphate
They are spherical soft and porous
Stabilised by kappa casein on the surface
Calcium phosphate acts as a bridge between micelles
18
Q
What are the 4 major proteins within whey?
A
- beta-lactoglobulin
- alpha- lactalbumin
- bovine serum albumin
- immunoglobin
19
Q
Which major protein is soluble at a pH of 4.6?
A
Whey
20
Q
Which protein has rennet coagulation?
A
Casein
21
Q
Which protein has high heat stability?
A
Casein
22
Q
Which protein has the greater particle size?
A
Casein
23
Q
What are two types of minor whey protein?
A
- Lactoferrins: bind iron
- Immunoglobulins: give immunity against bacteria
3 classes: IgA, IgG, IgM
24
Q
True or false: Changes in freezing point of milk can indicate its adulteration with water.
A
True
25
In what phase are mineral in milk found?
Both in serum (soluble) and in colloidal phase
26
What is the spoilage point of milk?
1 million bacteria per ml
27
At what temperature does milk leave the udder?
~37•C
28
What temperature is milk cooled to after leaving the udder? Why?
Must be cooled to 4 degrees as the shelf life of raw milk is only a couple of hours
29
What is milk tested for when arriving at milk factory?
- taste and smell
- composition
- antibodies
- freezing point depression
- pH/acidity
30
Why is standardisation of milk required?
- continuously required to meet legal requirements
- to maintain quality
- to meet processing parameters e..g for cheese
31
How is milk fat separated? Why are the requirements for this?
Sedimentation naturally occurs due to gravity, however this is not at a fast enough rate for commercial use
The milk must:
- be a dispersion
- phases to be separated must not be soluble in each other
- phases must have different densities
In commercial operations this is sped up by centrifuge
32
How is milk protein separated?
By membrane filtration, which involves a semi permeable very thin membrane allowing some molecules to pass through and others to be trapped
33
What is permeate?
The filtrate or liquid molecules which pass through the membrane
Contains all the components of milk except protein
34
What is retentate?
The concentrate or the liquid retained
35
What are the membrane processes?
Reverse osmosis: concentration of solution by the removal of water
Nanofiltration: concentration of organic compounds by removal of part of a monovalent ion like sodium + chlorine
Ultrafiltration: concentration of large macromolecules
Microfiltration: removal of bacteria and separation of macromolecules
36
What is homogenisation?
a standard industry procedure to stabilize the fat against gravity separation.
It involves breaking the fat molecules into smaller molecules so that they do not rise to the top
Milk is forced through a small passage at a high velocity and disintegration of fat is achieved by turbulence and cavitation
37
What are the advantages to homogenisation of milk?
- less cream formation
- whiter
- reduced sensitivity to fat oxidisation
- better mouthfeel
- better stability
38
What are the disadvantages to homogenisation?
- increased sensitivity to light (sunlight flavour)
| - may be unsuitable for semi hard and hard cheeses
39
What is the purpose of heat treating milk?
Heat treating reduces or destroys enzymes and bacteria to give milk a longer shelf life
40
What are the 5 different types of heat treated milk?
Pasteurized milk
Thermisation
ESL (extended shelf life)
UHT (ultra heat treated)
In-container sterilisation
41
What is thermisation of milk?
60-65 degrees for 5-15 seconds
Reduces psychotropic bacteria
However in Australia you cannot heat treat twice so this method is rarely used
42
What is pasteurisation?
The most widely used method, varies from country to country, but involved significant reduction of spoiling microorganisms and destruction of all pathogenic bacteria
Kills pathogenic bacteria and destroys some undesirable enzymes
Must be pasteurised by:
- heating to no less than 72°C for 15 sec
- or any other time/temp combination that has equal or greater lethal effect
Does not effect taste, colour or nutritional content
43
How is pasteurisation efficiency tested?
An alkaline phosphatase test is used as an indicator of pasteurisation
If safe the enzyme will be inactive as it has the same denaturation point as pathogens
44
What are the two types of pasteurisation?
Batch Pasteurisation (Low temp, long time)
Continuous Pasteurisation (high temp, short time)
45
Explain how batch pasteurisation works
Uses a vat pasteuriser where milk is in a cavity and hot water is in a jacket
Agitator is used when milk is being heated
Milk is cooled in the vat, hot water is replaced with cold water
46
How does continuous pasteurisation work?
Using a plate heat exchanger
A stack of stainless steele plates in a frame are heated by hot water, heat is then transferred to milk
Plates are extremely thin so heat transfers rapidly
Milk then passes through to cooling section
47
What are the minor changes that occur during pasteurisation?
- small amount of denaturation of whey protein
- minor damage to water soluble vitamins
- inactivates milk lipase and alkaline phosphates
48
What is the shelf life of pasteurised milk?
12-16 days
49
What is extended shelf life milk?
No single definition
Extended shelf life beyond pasteurisation, can be weeks to months
3 different processing technologies:
- pasteurization combined with bactofugation or double bactofugation
- pasteurisation combined with microfiltration
- high heat treatment: ~120-130°C for 2-5 seconds
Packed under very clean but not aseptic conditions
Must be refrigerated
50
What is sterilisation?
Commerical sterilisation is when a product is heated very high (>100°C) and packed in airtight containers
Not necessarily free of all microorganisms but those that survive sterilisation are unlikely to grow
Can be packed before or after sterilisation
51
What is UHT?
Ultra heat treatment
Milk is heated at 130-150°C for 3-5 seconds
Any higher risks chemical damage is too short to be practical
UHT milk is packaged aseptically
Shelf life of over 6 months
52
What are the two methods of UHT?
Direct:
milk is heated with steam (gives less cooked flavour)
Indirect:
stainless steele barrier acts as a heat exchanger
53
Which method of UHT has the greater product quality loss?
Indirect
54
What effects does UHT have on milk colour?
Increases the whiteness/ opaqueness due to homogenisation and denaturation of whey protein and their associated with casein micelles
Can have increased browness due to maillard reaction between lysine of proteins and lactose, brown colour increases during storage
55
What effect does UHT have on flavour of milk?
Can result in a 'cooked' flavour
flavour reduces during storage
This is due to the denaturation of β-lactoglobulin (occurs at 70°C)
Can also get sterilized flavour due to maillard reaction
This flavour increases with storage
Stale flavour can occur due to fat oxidation
56
What effect does UHT have on proteins in milk?
Denaturation of whey proteins ranging between 60% and 100% denatured
Depends on heating regimen (indirect causes more denaturation than direct)
denatured β-lactoglobulin links to kappa-casein on the outside of casein micelles mainly via disulphide bonding
57
What effect does UHT have on enzymes in milk?
Most native enzymes are deactivated EXCEPT proteases
Proteases
Some bacterial enzymes from psychotropic bacterial contaminants of raw milk can survive
58
What effect does UHT have on rennet clotting?
Clotting rate is reduced to half of that of raw milk
This is due to the interaction of denatured β-lactoglobulin and kappa-casein preventing access of rennet to kappa-casein
UHT is not suitable for making cheese (requires rennet)
59
What is In-Container Sterilisation?
Milk is filled into cans and heated in retort (like a large pressure cooker) until interior of can reaches desired temp
Causes greatest chemical change to milk components
Mainly used for evaporated milk etc
105-120°C for 10-30 mins
60
What is the composition of cream?
40% fat in the form of intact fat globules dispersed in skim milk
61
In what state is fat when milk is separated from cream?
Liquid (between 38-60°C)
62
What are the concentrations of fat in cream and butter compared to milk?
Cream is 10x more concentrated
Butter is 20x more concentrated
63
How many litres of milk does it take to make 1L of cream?
10 litres of milk = 1 litre of cream
64
What is added to thickened cream?
Gelatin or vegetable gums
65
How is cream heat treated?
Usually pasteurised at ~75°C for 15 seconds
66
How is sour cream created?
Lactic acid bacteria is added to cream and heated at 20°C for 12-14 hours
Gives it a slightly sour and thicker flavour/texture
67
What is the composition of butter?
>80% milkfat
Water-in-oil emulsion
1.2% salt
Contains fat soluble vitamins
68
What are the steps involved in creating butter?
Ageing
Churning
Phase Inversion
Washing
Salting
69
What is the process of ageing in the making of butter?
Cream is subjected to controlled cooling designed to give good crystalline structure, taking 12-15 hours
Pasteurisation causes the fat within globules to liquify, when cream is cooled a proportion of these will crystallise
If cooling is rapid there will be many small crystals, if cooling is slow there will be fewer larger crystals
Larger crystals give softer butter
70
What is the process of churning in the making of butter?
Cream first whips, and then fat globule membranes rupture and then the globules coalesce and form butter 'grains'
This point is called 'breaking' or 'phase inversion' as the cream is broken into two phases: butter grains and buttermilk
Buttermilk is then drained off
The grains are then worked into a continuous fatty mass
71
What is 'phase inversion' in the process of making butter
The change from fat-in-water emulsion to a water-in-fat emulsion
72
What is 'washing' in the process of making butter?
The butter is washed after churning to remove any residue of buttermilk and milk solids but is rarely done these days
73
What is salting and what does it achieve in making butter?
Added to improve flavour and shelf life
Acts as a preservative
In continuous production a salt slurry is added
74
What is ripened butter?
Made from cream which has been cultured with lactic acid bacteria and has decreases pH
75
What are cereal based milks?
Oat milk and rice milk
76
What are legume based milks?
Soy milk and pea milk
77
What are vegetable based milks?
Potato milk
78
What are seed based milks?
flax seed and hemp milk
79
What are nut based milks?
almond milk, cashew milk, coconut milk
80
What are the processes involved in making milk alternatives
Raw material → extraction → separation → product formation → homogenisation → heat treatment → packaging
81
why do we consume milk?
Fucking yum
82
What are the 3 three main significances of consuming dairy milk?
In the US, milk contributes 8% of daily energy and 16% of dietary protein
Contributes 67% of dietary calcium
The lactose in bovine milk aids in the absorption and utilisation of micronutrients including calcium
83
What are the nutritional properties of plant based milks?
Vary greatly between milks and the addition of oils or sweeteners also effects this
Soy is the only one with similar protein content to cows milk
Most are lower in saturated fat and have similar caloric amounts to skim milk
84
What is the protein content of plant based milks?
Lower quality than cows milk
PDCAAS of cows milk: 120
Soy milk: 91
Almond: 30
85
What is the fat content of icecream?
Must be at least 9% to qualify in the ice cream category
Premium products typically have 12-13%
86
What are the 9 steps involved in the manufacturing of icecream
Mix preparation
Pasteurisation
Homogenisation
Chilling
Ageing
Soft freezing
Flavouring
Hardening
Storage
87
What is the typical composition of ice cream mix?
10% fat
11% non-fat milk solids
12% sugar
0.5% stabilisers
88
What is the role of fat in icecream mixture?
Gives creaminess and improves melting resistance by stabilising air cell structure
Usually from whole milk, cream, butter and vegetable fat
89
What is the role of non-fat milk solids in icecream mix?
Helps to stabilise the structure of the ice cream
Does this by its water-binding and emulsifying effect
Also has a positive effect on air distribution during freezing process
90
What is the role of stabiliser in ice cream mix?
Increase the viscosity of the mix and create body and texture
Controls the growth of crystals and improves melting resistance
e.g. gelatin and bean gum
91
What is the role of emulsifiers in the ice cream mix?
helps with freezing and controls excess churning of fat
e.g. egg yolk solids, glycerol monosterate
92
When are flavours added to ice cream?
Eccessences added before freezing and solids are added after freezing
93
Why is homogenisation essential for good ice cream?
Essential for good smooth texture and even distribution of ingredients
Reduces size of fat globules and increases surface area
94
What occurs during chilling and ageing of ice cream?
The mix is cooled to 2-5°C and then aged at this temp for 4 to 14 hours
This allows time for crystals to be formed and proteins and polysaccarides to be fully hydrated
95
What is soft freezing in the making of ice cream?
50% of water is frozen
ice cream is beaten to incorporate air
Fine even foam is formed
Occurs at 1-9°C
Gives a texture like soft serve
96
What occurs during hardening in the manufacturing of ice cream?
90% of water is frozen
Cooled to ~-30°C in a blast freezer, this should be as rapid as possible
Now must be stored at -18°C
Poor storage is detrimental to quality
97
Explain how emulsifiers work?
Emulsifiers compete with kappa casein for the surface area of fat globules, however emulsifiers are much smaller than caseins
This gives a very thin layer on the fat globule
This makes the globule thinner and weaker to agitation
When whipped the membranes break and the globules come together to make chains which turn into air bubbles to stabilise
98
What is overrun?
A measure of air in icecream
It is a percentage increase in the volume of ice cream greater than the amount of mix used to start with
Varies from 100-150%
99
What are the two main concerns with the shelf life and quality of ice cream?
Coarsness: due to large crystals from slow cooling or melting and refreezing
Sandiness: due to lactose crystals, occurs if lactose:water ratio is greater than 11:1
100
What occurs in the process of fermentation of dairy products?
Either rennet cleaves off the kappa casein from the surface of casein micelles which destabilises them, or lactic acid reduces pH which destabilises them, causing thickening and coagulation
Lactic acid also converts part of the lactose to lactic acid
The low pH inhibits growth of spoilage organisms
101
How is yoghurt distinguished from cheese?
In yoghurt the whey is NOT removed
102
What cultures are used in making yoghurt?
A blend ofStreptococcus thermophilus (ST) and Lactobacillus bulgaricus (LB) work symbiotically in a ratio of 1:1
ST grows faster and produces acid and CO2 which stimulates LB growth
LB further drops pH to ~4.5
103
What are the 4 steps involved in yoghurt making?
1) Fortification
2) Homogenisation
3) Heat Treatment
4) Fermentation
104
What occurs during the fortification step of yoghurt making?
Aims to improve consistency and flavour
Can increase solids to ~15% by addition of skim milk powder
Can also increase concentration by ultrafiltration
Can add pectin or gelatin at this stage for added viscosity
105
What occurs during homogenisation of yoghurt?
Gives good dispersion of ingredients and prevents the creaming of whey off the top during incubation
Increases viscosity and firmness
106
What occurs during the heat treatment of yoghurt?
This is unique to yoghurt
Varies between 85°C for 30 mins to 90°C for 10 mins
Produces a sterile environments and denatures whey protein
Helps casein network and shortens coagulation time
107
What occurs in the fermentation process of making yoghurt?
Occurs in a jacketed fermentation tank with hot water at approx 43°C
This temp is in between the optimum temps for LB and ST
NO agitation
Incubated with starter culture until pH is ~4.5 then jacket is replaced with cold water
Now fruit can be added and packaged
108
What is frozen yoghurt?
yoghurt either mixed with ice cream or ice cream mix which has been fermented before processing
109
What is probiotic yoghurt?
Contains either probiotics or prebiotics
Probiotics such as ABC cultures are added as well as LB and ST
Prebiotics such as inulin can also be added to act as substrates for gut bacteria
110
What is rennet?
An enzyme from the abomasum of dairy animals which coagulates milk
111
How does the coagulation of milk occur?
In three steps proteolysis → aggregation → gelation
Rennet cleaves the kappa caseins from the surface of casein micelles (proteolysis)
Then with heat and calcium ions these casein micelles gelatinise
112
What is ripened cheese and how is it classified?
accounts for 75% of all cheeses
Moisture and acid levels are lower than for fresh cheese
Can be stored for up to 2 years
Classified based on:
- texture
- method of production
- ripened or fresh
- types of microorganisms
113
What is added to milk in the cheese making process?
Calcium chloride to aid coagulation
Colouring
Bacterial Starters
Rennet
114
What happens to cheese during ripening?
microbiological, chemical and biochemical processes occur:
- lactose degradation and flavour development
- protein decomposition
- fat decomposition
- secondary metabolites
- residual rennet gives specific flavour
115
What is foam and what is the typical structure?
Foam is a dispersion of gas bubbles in a liquid or solid matrix
The structure is typically stabilised by the presence of absorbed protein at the fluid interface between the gaseous and aqueous phases
116
Which are the two main types of protein which make foam?
Egg white and milk
117
What is the foam ability/capacity?
The ease and extend of foam formation
118
What is foam stability?
The rate of loss of foam structure once formed
119
What effects foam capacity of a liquid?
Depends on the the protein having the capacity for rapid absorption and unfolding at the protein interface
120
What is foam stability dependent on?
Stability depends on the ability of the protein to form strong flexible cohesive film to reduce the gas permeability and inhibit bubble coalescence
121
What are included as dairy foams?
Whipped cream, mousses, meringues and soufflés
122
What are the 3 main ways in which the foaming capacity of a protein can be improved?
Making it more flexible
Exposing it to more hydrophobic residues
Reducing average molecular weight
123
What are the 4 requirement to make foam?
A gas
Water
A surfactant
Energy
124
How do surfactants work?
Acts as a foaming agent to lower the surface tension between gas and water and facilitate the formation of small gas bubbles
The surfactant absorbs at the interface and orients itself with the lipophilic group towards the non-polar phase (air) and the the hydrophobic group towards the polar phase (water) to lower surface tension
