1
Q
milk contains
A
lipids, proteins, salts, carbohydrates
2
Q
essential nutrients in milk
A
Vit A, Vit B12, riboflavin, calcium, potassium, magnesium, zinc, phosphorus, carbohydrate, protein
3
Q
raw milk
A
mimlk straight from animal
4
Q
biosynthesis of milk
A
- synthesised in mammary gland
complete milk producing unit - alveolus
5
Q
alveolus
A
- consists of secretary cells
- epithelial secretory cells surrounded by blood vessels
6
Q
lactose, fat and most proteins (casein) formed from?
A
substrates carried in the blood
7
Q
minerals, vitamins and certain proteins are
A
filtered out of blood
8
Q
composition of milk
A
- human milk has low casein and high lactose
9
Q
factors affecting milk compostion
A
- nutrition factors e.g. type and quality of feed
- non-nutritional factors e.g. breed, stage of location, season and temperature
10
Q
nutrition factors
A
type and quality of feed
11
Q
non-nutritional factors
A
- breed e.g. holstein breed have low fat and protein percentage
- stage of location
- season and temperature (e.g. more milk winter)
- age and size
- disease
- milking frequency
12
Q
colostrum
A
- first milk that cow produces after calving
- differs from normal milk in composition and properties (yellowish, salty, high serum protein and antibodies)
- within 72 hours compositino returns to that of fresh milk
13
Q
effect of milk composition
A
- physio-chemical properties
- functional properties
- pricing of milk: based on fat and protein solids, varies between manufacturers, states and individual farmers
14
Q
physical properties of milk
A
- appearance
- density
- osmotic pressure
- freezing point
- pH and acidity
15
Q
appearance of milk
A
- opacity - due to suspended particles of fat, protein and certain minerals
- colour - white to slight yellow (due to carotene content)
16
Q
density of milk
A
- 1.028 - 1.033 g/cm3 20 degrees
17
Q
osmotic pressure of milk
A
- isotonic
18
Q
freezing point of milk
A
- 0.512 to -0.59 degrees
19
Q
pH and acidity of molk
A
- important indicator of microbial quality of raw milk
- conc. of H+ ion
- pH fresh milk = 6.6-6.8
- acidity = 0.13% lactic acid
20
Q
components of milk
A
- fat globules
- casein micelles
- whey proteins
- lactose, salts and others
21
Q
milk fat
A
- lipids soluble in non-polar organic solvents and insoluble or sparingly soluble in water water
- 87% water
- is an oil in water emulsion
- exists as small globules or droplets dispersed in the milk serum (0.1-20um diameter)
22
Q
fat globule
A
- enveloped by a biological membrane similiar to that of a blood cells
- acts as an emulsifier
23
Q
main classes of lipids
A
table in slides
24
Q
fatty acid composition of triclglycerols (TAGS)
A
- several hundred
- 15FA’s - 95% present in TAGS
- sat FA - C4-C20
70% total FA’s under normal conditions - unsat FAs - mono, dienes, trienes
- low levels of polyunsat acids - C18:2 (approx 2%)
- C16, C18 and C18:1 are most abundant
- C4 is unique to milk fat
25
TAG
- possible - 15 major FAs therefore 15*15*15b - 3375
- distribution of FA's over position in TAG are not random;
C4 and C6 mostly in 3-position, C18 mostly in 1-position
- positioning affects crystalisation
26
Milk fat globule membrane (MFGM)
- completely covers milk fat globule
- originates from plasma membrane of mammary secretory cell
- reddish brown colour (due to xanthine oxidase)
- 2-6% total mass of fat globules
27
Function of MFDM
- dispersion of fat in aqueous phase of milk
| - protection of fat from lipase
28
MFGM consists of proteins, lipids and carbs in approx ratio of
4:3:1
29
minor lipid components in milk
sterols
carotenoids
fat soluble vitamisn
30
sterols in milk
- class of lipid that are present in small qualities
| - cholesterol represents 95% of total sterole present in bovine milk
31
carotenoids in milk
- present at trace level
- beta carotene - 95% total carotenoids
- situated solelt in core of fat globules
- absent from MFGM
32
Fat soluble vitamins in milk
Vit A - approx 40IU/g milk fat
Vit E - approx 0.025-0.05IU/g fat
Vit D and K - very low concentration
33
proteins in milk
Amino acids (AA) building blocks
- linked together in linear polymer chains (polypeptide chain)
proteins consist of 1 or more polypeptide chains bonded together and may be coiled or folded
34
2 major types of milk protein
- casein 80%
- whey 30%
minor type - membrane proteins (fat globule membrane and skim milk membranes)
35
Casein in milk
- exist as colloidal particles
- insoluble at pH 4.6 and 20 degrees
- come on top of the fat globule and help them to be stabilised(?) in milk
36
casein major types
- alpha S1, alpha S2, beta and K caseins (ratio of 40:10:35:12)
- synthesised in secretory cells
37
casein minor types
- y-casein and proteose peptone and upside down y-casein
| - produced after secretion of milk
38
casein micelle
- contains 95% of casein
- av MW approx 10^8 daltons , diameter 50-500nm
- 94% protein, 6% colloidal calcium phosphate
- 2g water/g protein
- discreet particles stabilised by K-casein on surface
- hydrophilic C-terminal end protudes to give micelle hairy appearance
39
Whey
- casein-derived peptide in cheese whey
| - about 60 enzymes from blood and secretory cells in mammory gland
40
whey major proteins
- beta-lactoglobulin (2-4g/L)
- alpha-lactalbumin (1-1.5 g/L)
- bovine serum albumin (0.1-0.4 g/L)
- immunoglobulin (0.6-1g/L)
41
whey minor proteins
- lactoferrin
| - immunoglobulilns
42
lactoferrin
- equivalent to transferrin in blood
- has antimicrobial properties
- binds iron (basis of antimicrobial properties)
- fragments (lactoferricin) obrained by treating lactoferrin with a proteinase enzyme thats antibacterial
heat sensitive - denatures at about 65 degrees
43
immunoglobulins
- high conc. in colostrum (10% total N)
- 3 classes exist in milk - A, G, M
- provides protection against bacteria and rotavirus infection in children
- produced by hyperimmune cows
44
Lactose
- carb in milk
- least soluble of common sugars
- can cause defects in concentrated milk and frozen fairy products
- low sweetness
45
deficiency of lactose can cause
lactose intolerance
46
lactose is made of
glucose and galactose
47
minerals in milk
- Ca, Mg, K, Na
- bicarbonate, chloride, citrate salts
- distributed between soluble and colloidal phase
- 66% calcium and 55% phosphorus in collodial phase
- affects stability of milk and milk products
- maintains osmotic pressure
48
milk enzymes
- some originate in blood
- some synthesised in mammary secretory cells
- some have found commerical applications
- some cause quality problems in milk and milk products
49
milk cooling
- milk leaves udder at temp of 37 degrees
- contaminated with microbes (even before leaving udder)
- further infection of milk by microorganism can take place during milking, handling (e.g. cow skin, hair etc), storage and other pre-processing activities
50
bacteria in milk
- multiply as soon as gets into milk
- milk is generally very rich in nutrients - ideal growth environment for many microorganisms
- water activity of milk is 0.98 - suitable for growth of bacteria
- pH is 6.6 - ideal for microbial growth
51
milk spoiling
- just a few hours
- must be cooled dwon to 4 degrees immediately after milking
- keep at low temp during storage and transportation
52
preparation of milk
reception of raw milk - testing of milk for quality
| quality assurance of raw milk - - sensory, composition, antibiotics, freezing point depression, pH/acidity
53
standardisation of milk
- milks all come from different farms therefore has different properties
- standardised to have a constant quality of milk and also milk products (e.g. cheese)
- should have min 3.2 percent fat and 3 percent protein
54
standardisation of fat
skimming, adding cream
55
standardisation of protein
adding permeate
56
milk fat separation
- gravity
57
milk - sedimentation
1. The liquid to be treated must be a dispersion (a mixture of two or more phases), one of which is continuous:
• In milk it is the milk serum, or skim milk, that is the continuous phase.
• Fat is dispersed in the skim milk in the form of globules
2. The phases to be separated must not be soluble in each other (Fat is insoluble in serum)
3. The phases to be separated must also have different densities:
• the fat globules have a lower density.
58
If the density of the object is higher than that of the liquid, it will
sink, but it will float if the density of the object is lower.
59
If milk left in vessel
fat solubles will aggregate and float to the top of the milk - this could be skimmed of by hand but would be very slow, now have centrifugal force to separate
60
milk proteins are ___ than fat globules
much smaller
61
membrane
- semi-permeable membrane is a very thin film that allows some types of matter to pass through while leaving others behind
62
permeate
- filtrate, liquid passing through membrane
- all components of milk except protein
- added to milk to dilute protein (won't change anything else)
63
feed
- solution to be concentrated or fractionated
64
retenate
- the concentrate, retained liquid
65
membrane process
Reverse Osmosis (RO)
Nanofiltration (NF)
Ultrafiltration (UF)
Microfiltration (MF)
66
Reverse Osmosis
- concentration of solutions by removal of water
67
Nanofiltration
- concentration of organic components by removal of part of monovalent ions like sodium and chlorine (partial demineralization)
68
Ultrafiltration
- concentration of large and macro molecules, for example proteins
69
Microfiltration
- removal of bacteria, separation of macromolecules
70
Homogenisation
- stops separation of fats
- breaks fat globules into smaller ones
- stabilises fat against gravity separation
- diminishes creaming
- uses turbulence and cavitation
71
advantages of homogenisation
- Smaller fat globules leading to less cream-line formation
- Whiter and more appetizing colour
- Reduced sensitivity to fat oxidation
- More full-bodied flavour, and better mouthfeel
- Better stability of cultured milk products
72
Disadvantages of homogenisation
- Somewhat increased sensitivity to light (sunlight and fluorescent tubes) can result in “sunlight flavour”
- The milk might be less suitable for production of semi-hard or hard cheeses because the coagulum will be too soft and difficult to dewater
73
five major heat treatments of milk in order of increasing severity
- Thermisation
- Pasteurisation
- High temperature pasteurisation (ESL, Extended Shelf Life processing)
- Ultra High Temperature(UHT) treatment (or Ultra Heat Treatment)
- In-container sterilisation
74
Thermisation
heat treatment - 60-65% for 5-15 seconds
- milder than and enables storage/transport for longer before pasteurisation
- reduces bacterial count and production of degrading enzymes
75
thermisation does not
- inactive alkaline phosphatase
| - ensure destruction of pathogenic bacteria
76
Pasteurisation
- most effective (and common) control measure for eliminating pathogens that may be present in raw milk
77
Pasteurisation purpose
- destroying all bacteria that may be harmful to health (pathogens)
- destroying some undesirable enzymes and many spoilage bacteria
78
Pasteurisation shelf life
7, 10, 14 or up to 16 days
- has 12-16 days shelf life
- not packaged aspetically
- spoilage is usually due to post-pasteurisation contamination of the milk by psychrotrophic bacteria - thermodurics are minor spoilage organisms compared with psychrotrophs.
79
Pasteurisation Regulations
- varies from country to country
- common requirement in all countries is that the heat treatment must guarantee significant reduction of spoiling microorganisms and destruction of all pathogenic bacteria, without the product being damaged.
80
Pasteurisation Regulations in Australia
Milk must be pasteurised by
- heating to a temperature of no less than 72°C and retaining at such
temperature for no less than 15 secs
- heating, using any other time and temperature combination of
equivalent or greater lethal effect on any pathogenic micro-organisms in
the milk
- using any other process that provides an equivalent or greater lethal effect on any pathogenic micro- organisms;
unless an applicable law of a State or Territory otherwise expressly provides
81
Pasteurisation efficiency
Alkaline phosphatase test as an indicator of efficiency of pasteurization
82
The two processes of pasteurisation are
Batch - long time, low temp
| Continous - short time, high temp
83
Batch method
- uses a vat pasteurizer
- surrounded by either circulating water, steam or heating coils of water or steam
- milk is heated and held throughout the holding period while being agitated
- must cool down milk to ocmplete pasteurisation
84
Continous (HTST)
- plate heat exchanger
- hot water on opposite sides of plates heat milk to a temp of at least 72 degrees
- flows through to the holding tube where is held for at least 16 seconds
- warm milk passes thorugh cooling section - cooled to 4 degrees
85
pasteurisation minor changes to milk components
- Inactivates milk lipase and alkaline phosphatase (used as test for pasteurisation)
- Causes a little denaturation of whey proteins, particularly beta-Lg
- Very little destruction of vitamins - small loss of water- soluble vitamins
- Small change in flavour
- Little change to fats, lactose and minerals
86
Extented shelf life technology (ESL)
- the ability to extend the shelf life of a product beyond its traditional life by reducing the major sources of reinfection and maintaining the quality of the product all the way from milk producer to the consumer
87
ESL three main processing technologies
1 - Pasteurization combined with bactofugation or double bactofugation
2 - Pasteurization combined with microfiltration
3 - High heat treatment (HHT)
88
ESL - using high heat
- Heating conditions are between pasteurisation and UHT, usually 120-130 degrees for around 2-5 seconds
- packaged under clean but not aseptic conditions
- must be refrigerated stored
- several weeks longer shelf life than pasteurised but not as long at UHT
- some heat-resistant sporeformers remain but aim to kill most
89
Sterilisation
- made commercially sterile by subjecting it to temperatures in excess of 100° C, and packaging it in air-tight containers
- can be packaged before or after sterilisation (this is difference between UHT and in-can sterilisation)
90
Commercial Sterilisation
- a product is not necessarily free of all microorganisms, but those that survive the sterilization process are unlikely to grow during storage and cause product spoilage
91
UHT
sterilisation of food before packaging, then filling into pre-sterilized containers in a sterile atmosphere.
92
In-can sterilisation
sterilisation of food while in containers in a sterile atmosphere
93
UHT treatment
- 130-150 degree for 3-5sec
- if lower - time too long
- if higher - time too short
- can be stored at room temperature
- packaged aseptically
- shelf life approx 6 months
94
two main types of UHT processing
- direct heating
| - indirect heating
95
UHT - Direct heating
- milk is mixed directly with steam
- heating by transfer of latent heat from steam
- the product is held at the elevated temperature for a shorter period of time
- This means less damage, less cooked flavour (better flavor and quality)
- need quality steam (converted to water - dilutes milk 11 percent water)
96
UHT - Indirect heating
- milk is heated in a heat exchanger: steam or hot water heats a stainless steel barrier which heats the milk
- no direct contact between steam and milk therefore longer time
- quality of steam not important
- no dilution, more flavour change
97
Two types of direct heating
- Injection or steam- into-milk
- infusion or milk-into-steam
- both types give rapid heating - less than 1 sec to
reach approx 140°C from approx 75°C)
98
UHT - caused changes in milk
```
colour
flavour
denaturation of why proteins
enzymes
vitamin destruction
rennet clotting ability
```
99
UHT - colour changes in milk
- Increased whiteness/opaqueness due to homogenisation and denaturation of whey proteins and their association with the casein micelles.
- Increased brownness due to Maillard reaction between lysine of proteins and lactose; brown colour increases during storage.
100
UHT - flavour changes in milk
3 major types of flavour
- ‘cooked flavour’ due to liberation of -SH groups from denatured beta - lactoglobulin (this starts at approx 70°C). Decreases during the first few days after processing due to oxidation from dissolved oxygen
- ‘sterilised flavour’ resulting from Maillard reaction (this starts at approx 90°C). Does not decrease during storage and may intensify.
- ‘stale flavour’ from fat oxidation – mainly due to aliphatic aldehydes and methyl ketones.
101
UHT - denaturation of whey proteins in milk
From 60% to 100% denaturation of whey proteins
- Amount of denaturation depends on heating regime (indirect heating causes more than direct heating)
- denatured beta-lg links to K-casein on outside of casein micelles mainly via -S--S- (dislphide bonds)
102
UHT - enzymes changes in milk
- Most native milk enzymes are inactivated except proteases, eg. milk alkaline protease or plasmin.
- But proteases and lipase (bacterial enzymes) from psychrotrophic bacterial contaminants of raw milk can survive UHT treatment (some are 400 times as heat resistant as B. stearothermophilus)
- Proteases cause age gelation and bitter flavours.
- Lipases cause rancid flavours
103
UHT - vitamin destruction in milk
- No effect on fat-soluble vitamins
- Small losses of water-soluble vitamins, eg thiamine (B1), B6 and B12;folic acid and ascorbic acid (C) reduced also but mainly through oxidation and heat
- Vitamin content decreases further during storage
104
UHT - rennet clotting ability changes in milk
- Clotting rate reduced to half that of raw milk
- Due to interaction of denatured beta-Lg and K-casein preventing
access of rennet to K-casein
• Therefore UHT milk is not suitable for making cheese which requires rennet action
105
In-container sterilisation (retorting)
- Most severe of heat treatments
- Causes greatest chemical change to milk components
- used for concentrated milks such as evaporated milk
- 105-120 degrees/ 10-30mins
- slows heat and cool down times
- causes marked changes in flavour (cooked, caramelised), colour (brown), water soluble vit destruction of milk
- greater shelf-stability at room temp than UHT
106
how in-container sterilisation (retorting) is done
- milk is filled into cans and heated in a retort until the interior of the can has reached the desired temperature for the desired time
107
comparison of sterilisation method - in container
- Slow heat penetration
- Uneven heating
- More severe heat treatment
- Less difficulty with particulates
108
comparison of sterilisation method - UHT
- Shorter heating/cooling times
- More even heating
- Less quality loss
- High temperatures possible
- Packaging size does not affect processing conditions
109
Market milk types available
- Pasteurised: UHT& ESL
- Whole milk: contains approx 3.4% fat
- Reduced-fat milk: contains approx 2% fat
- Skim milk: contains approx 0.1% fat
110
A2 milk
only A2 genetic variants of B-casein
| no A1 variant
111
major fat products in milk
cream
butter
AMF/butteroil
112
cream fat conc.
represents about 10 fold conc of fat compared with milk
113
butter fat conc.
represents about a 20-fold concentration of fat compared with milk (2-fold compared with cream)
114
AMF fat conc.
represents >99% milk fat.
115
Emulsion
- dispersion of one fluid into another
- fluids normally immiscible, one of the fluids dispersed as small spherical droplets in the other
- substance that makes up droplets in an emulsion is in the discontinuous, dispersed or internal phase.
- substance that makes up the surrounding fluid is called the continuous or external phase
- An emulsion is formed when oil, water, and an emulsifier are mixed together
- The emulsifier coats the emulsion droplets and prevents them from coalescing or recombining with eachother
116
two types of emulsions
oil in water emulsion
| water in oil emulsion
117
oil in water emulsion
Oil droplets dispersed in aqueous phase
118
water in oil emulsion
Water droplets dispersed in oil phase
119
Cream
- produced from milk by centrifugal separation (lighter fat globules rise to top under centrifugation
- separation at 38-60 degree (fat is liquid) - generally 55 percent
- excess physcial handling can rupture fat globules and cause lipolysis
120
separation of milk yields
cream - 40 percent of fat in form of intact fat globules in skim milk
skim milk - less than 1 percent fat in form of V small fat globules
121
Cream yielded from milk
- usually 10 litres of milk yield 1 litre of cream.
- creams with a range of fat contents can be produced by either adjusting the separator or diluting the 40% fat cream
- Reprocessing cream through a separator produces a higher-fat cream (possibly 60% fat)
122
Cream range (didnt do much on this)
• 35% Milk Fat Content
May be called Regular Cream, Pure (pouring or thin)
• 45%–60% Milk Fat Content
May be called Rich, Double, Pure Rich
• 18% Milk Fat Content May be called Lite
• Thickened Cream (regular, rich or reduced fat)
• Clotted/Scalded Cream
With a slight caramelised flavour, no less than 48% milk fat
• Sour Cream
LAB culture is added and the cream is heated to about 20°C for 12–14 hours. The lactic acid produced in this process gives a slightly sour taste and a thicker than normal consistency.
• Long Life Cream (UHT)
Available in cartons, usually contains 35% milk fat.
• Canned Reduced Fat Cream
Reduced fat cream, with 21% milk fat, is packaged and heat-sterilised to extend its life. In- container sterlisation. Available in cans or cartons.
123
Butter
- water in oil emulsion
- approx 80% milkfat, 16% water, 1.2% salt, 1.2% protein,calcium and phosphorus
- contains Vit A, D and E
124
butter made by
- churning' pasteurised cream (40% fat) at cool temperatures (less than 10 degrees)
- churning involves agitation/whipping or continuous mixing in rolling barrel
can use hand to churn by shaking in container (e.g. glass bottle)
125
Butter classification
main
- Sweet cream butter
- Cultured or sour cream butter made from bacteriologically soured cream
also classified according ot salt content
- unsalted
- salted
- extra salted
126
cream aging
- Aging takes 12 - 15 hours
- Pasteurization causes the fat in the fat globules to liquefy
- When cream is cooled a proportion of the fat will crystallize
• If cooling is rapid,lots of small crystals; if gradual the yield will be fewer but larger crystals.
• Larger crystals give softer butter
127
Churning - cream
- fat globule membranes rupture, the fat globules coalesce and form butter 'grains' (called breaking or phase inversion)
- The cream is broken into two phases: butter grains and buttermilk
- The buttermilk is drained off
- The butter grains are then 'worked' or 'plasticised' into a continuous fatty mass (butter) and to break up embedded pockets of buttermilk or water into tiny droplets
128
Churning - butter
- fat is the continuous phase and water, in the form of small droplets, is the discontinuous phase
- The water droplets must be small (approx 2-4 um in diameter) and evenly dispersed in the fat
- The small water droplets prevent growth of bacteria; poorly worked butter has an uneven distribution and sizes of water droplets which allow bacterial growth
129
phase inversion
refers to the change from a fat-in- water emulsion (cream) to a water-in-fat emulsion (butter) - part of churning
130
breaking point
breaking the molecule
131
butter - washing
- washed after churning to remove any residual buttermilk and milk solids
- Rarely done anymore
132
butter - salting
- Salt is used to improve the flavour and the shelf-life (acts as a preservative)
- In batch production salt (1-3%) is spread over its surface
- In the continuous butter maker, a salt slurry is added to the butter
- salt fully dissolved in aqueous phase, so the effective salt conc is approx 10% in water
- after salting, butter must be worked vigorously to ensure even distribution of salt
133
Buttermilk
skim milk plus milk fat globule membrane material
| - butter formation from cream is opposite to homogenisation
134
ripened butter
- made from cream cultured with lactic acid bacteria which produce diacetyl and lactic acid; has reduced pH due to lactic acid; often unsalted.
- mixed cultures of S. cremoris, S. lactis diacetyl lactis, Leuconostocs used
- Cream is ripened to pH 5.5 at 21 degrees and then pH 4.6 at 13 degrees before churning
- Not washed or salted
135
butter structure
moisture droplets - contain SNF and salt
fat globules - partially crystalline
non globular fat - continous phase
fat crystals - semi-continous networks
136
longertime equals ___ butter
better
137
plant based milk substitutes
water extracts of legumes, oil seeds, cereals, or pseudocereals that resemble cow's milk in appearance
138
general outline of process of plant based milk substitutes
the plant material is either soaked and wet milled or the raw material is dry milled, and the flour is extracted in water afterwards
139
general manufacturing process of plant based milk substitutes
raw materials -> extraction ->separation -> further product formulation -> homogenisation -> heat treatment -> packaging
140
nutritional properties of plant based milk
screenshot
| - only soy milk has values comparable to cows milk in regards to protein
141
protein deficiency
- kwashiorkor
- stunted growth
- muscle wasting
- weakened immunity
- increased risk of cardiovascular disease
- diabetes
- cancer
- osteoporosis
- obesity
142
protein efficiency ratio and PDCAAS values
screenshotted
| - soy, quinoa and amaranth highest after cows milk
143
Calcium functions
- vascular contraction and vasodilation
- muscle function
- nerve transmission
- intracellular signalling
- hormone secretion
144
plant based milk alternatives when fortified often contain ____ calcium amounts compared to ___ milk
higher calcium; bovine milk
145
one serving of ___ bovine milk contains ___ mg of calcium
2 percent; 120mg calcium
146
unfortified milk and milk alternatives had ____
drastically lower levels of calcium
147
Ice cream manufacturing
- mix prep
- pasteurisation
- homogenisation
- chilling
- aging
- soft freezing
- flavour/fruit added
- hardening
- storage
148
Ice cream mix contains
10% fat
11% MSNF
13% sugar
0.5% stabiliser/emulsifier
149
Fat - Ice cream
- 10-15% of ice cream
- gives creaminess and improves melting resistance by stabilising the air cell structure of the ice cream
- from whole milk, cream, butter or anhydrous milk fat (or can be coconut oil or palm kernel oil as vege fat)
150
MSNF - ice cream
- From whole milk, skim milk, condensed milk, milk powders and/or whey powder. High nutritional value
- Helps to stabilize the structure of ice cream due to its water-binding and emulsifying effect. The same effect also has a positive influence on air distribution in the ice cream during the freezing process, leading to improved body and creaminess.
151
Sweeteners - ice cream
- Increase the solids content of the ice cream and give it the level of sweetness consumers prefer.
- Can be sugar, glucose syrups, honey, or sweeteners such as aspartame, acesulfame K, sucralose (in sugar free ice cream).
152
Stabilisers - Ice cream
- Increase the viscosity of the mix and create body and texture
- Control the growth of ice crystals and improve melting resistance: gelatin, carrageenan, carboxymethylcellulose (CMC), locust bean gum,
guar gum
153
Emulsifiers - ice cream
- Egg yolk solids, glycerol monostearate (GMS). Help with freezing
- Also controls excess churning of fat during the freezing process
- compete with casein to be on surface of fat globule (replace casein - thin layer on top of fat globule)
154
Flavours - ice cream
- Essences added before freezing, solids (nuts, fruit, etc) added after freezing
- Chocolate added to mix before pasteurisation as it often contains undesirable bacteria. The most popular flavours are vanilla, chocolate and strawberry
155
Ice cream mix preparation
Mixture usually heated to 50-600C to effect good mixing - if GMS is used, mix at > 600C, the melting point of GMS
156
Ice cream pasteurisation
- usually 8085 degrees/ 15-30 sec
157
Ice cream homogenisation
- Essential for good smooth texture and even dispersion of ingredients
- Usually at approx 75 degree
- Reduces size of fat globules
- Increases surface area
- Forms membrane
- Makes possible the use of butter, frozen cream, etc
- Controls whippibility and churning during freezing
158
Ice cream chilling and ageing
- Mix is cooled to 2-5degrees and aged at this temp
- Ageing allows time for the fat to cool down and crystallize, and for the proteins and polysaccharides to fully hydrate and stabiliser gel formation
• 4-24 hours depending on stabiliser used (gelatin takes 24 hr)
159
ice cream freezing
approx 50% water is frozen
- Beating to incorporate clean air and freezing in scraped surface heat exchanger
- Fine even foam required, freezing rapid
- Temp. at outlet of freezer -1 to -9 degree.
- Packaged when soft unless other steps required, eg, addition of particulate matter such as fruits, nuts, candy, cookies
- At this stage, consistency same as soft serve ice cream
160
Ice cream hardening
approx 90% water frozen
- Ice cream cooled to approx -35 degree in a blast freezer; should be as rapid as possible to ensure small ice crystals
- Must be stored at < -18degrees after hardening
- Poor storage conditions (freezer temp. too high or fluctuating) in shops and at home are detrimental to ice cream quality
161
Ice cream structure
Has complex physical structure
- an emulsion of 3 phases:
- Solids (ice crystals, fat, protein, lactose crystals)
- Liquid (unfrozen water)
- Gas(air)
162
Ice cream overrun
% Overrun = (Vol. of ice cream - Vol. of mix used)/Vol. of mix used x 100% • Example : 500 L mix gives 980 L ice cream
varies from 100-150%
163
% increase in volume of ice cream ___ than the amount of mix used to produce that ice cream
greater
| e.g. start with 1L of mix and makes 1.5L of ice cream
164
Ice cream shelf life
- Only consideration is texture defects
| - Texture should be smooth
165
Problems with ice cream shelf life
- coarseness due to large ice crystals
- Fine ice crystals result from rapid cooling; large crystals from slow cooling or melting/refreezing or fluctuating storage temperatures
- sandiness due to lactose crystals - can occur if lactose: water ratio is > 11:1 (lactose comes from skim milk powder added).
166
Maintaining shelf life of ice cream
- Formulate the ice cream properly
- sugar considerations
- Stabilizers: bind free water
- Freeze the ice cream quickly
- Harden the ice cream rapidly
- Avoid temperature fluctuations during storage and distribution
167
yoghurt
- generic term which includes a range of fermented milk products
- distinguished from cheeses by not removing whey from the coagulated casein or curd
168
Yoghurt ingredients
- usually cow milk
may also include
- other dairy products e.g. whey, lactose
- sweetners e.g. glucose or sucrose
- stabilisers e.g. gelatin, carboxymethyl cellulose
- flavours
- fruit prep e.g. natural and artificial flavouring
169
Yogurt cultures
- Symbiotic blend of Streptococcus thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB); Ratio approx 1:1
- These microorganisms are ultimately responsible for the formation of typical yogurt flavour and texture
- work symbiotically
170
ST
Streptococcus thermophilus
- grows faster and produces both acid and carbon dioxide which stimulates LB growth
- drop initial pH to approx 5.0
171
LB
Lactobacillus delbrueckii subsp. bulgaricus
- The proteolytic activity of LB produces stimulatory peptides and amino acids for use by ST
- further decreases pH to approx 4.5
172
Fundamentals of yoghurt making
- The best possible growth conditions must be created for the starter culture
- The milk must be held at the optimum temperature for the relevant starter culture
- The cultured milk must be cooled quickly at the end, to stop the fermentation process.
173
Yoghurt productioin
- Fortification of milk to increase milk solids-not-fat
- Homogenisation at 50-60 degrees
- Heat treatment - 85 degrees/30 min. to 90-95degrees/10-20 min
- Cool to 40-45 degrees
- Add starter cultures
- Incubate till firm gel forms (5-7 hours)
- Stir (for stirred yogurt) & cool
- Add fruit if required
- Store/dispatch
174
Yoghurt fortification
- To improve consistency (viscosity) and flavour of yoghurt
- Total solids ~14-15% for low fat yoghurts - mostly by adding skim milk powder at 3-6% (can have much higher levels due to added sugar, fruit, etc)
- Can concentrate milk by ultrafiltration to 18-20% solids
- Sometimes pectin or starch or gelatin is added
to increase viscosity
- Yoghurts can also be made with fat substitutes replacing the milk fat - starch-based and microparticulated protein-based fat substitutes quite successful
175
homogenisation of yoghurt
- To effect homogeneous dispersion of constituents, SNF and fat
- To prevent creaming and wheying off during incubation and storage
- To improve viscosity and firmness of coagulum
176
Yoghurt heat treatment
- Unique to yoghurt manufacture
- Varies-85 degree/30min to90-95 degree/10-20min
- produce a relatively sterile and conducive environment for the starter culture
- denature and coagulate whey proteins (about 70–80% of the whey proteins)
- Helps formation of casein network
- Increases gel firmness and decreases
syneresis (release of whey from gel)
- Shortens coagulation time, increases pH at which coagulation occurs
177
Yoghurt fermentation
- jacketed fermentation tank filled with hot water
- 43 degree maintained under quiescent conditions
- incubated with starter culter until pH is 4.5 (due to production of lactic acid)
- jacket replaced with cool water and agitation begins (stops fermentation)
- coagulated product cooled to 5-22 degree
- product then cooled and stored at 5 degree to slow down physical, chemical and microbiological degredation
- packaged immediately after inoculation
178
types of yoghurt
- set
- stirred
- drinking type
- frozen type
- concentrated
- plain/natural
179
Set yoghurt
incubated in container; additives such as fruit sink to bottom
180
Stirred yoghurt
incubated in tanks; gel disrupted by stirring, pumping, filling, additives well suspended
181
Drinking yoghurt
similar to stirred except the coagulum is broken down to a liquid
182
frozen yoghurt
incubated in tanks and frozen like ice cream
manufactured in two ways
Either, the yoghurt is mixed with an ice cream
mix or an ice cream mix is fermented, before further processing.
183
concentrated yoghurt
incubated in tanks, concentrated and cooled before being packed e.g. greek yoghurt
184
probiotic yoghurt
contain
- L. acidophilus, a common bacteria of the human gut; able to colonise the gut whereas L. bulgaricus cannot.
- Bifidobacteria (Bifidobacterium longum or B. bifidum)
- L. casei
produce acid slowly compared with the normal yoghurt starters so are usually added in addition to ST and LB
- inulin often added as well
185
Cheese
- Group of fermented milk-based food products
- Cheese = casein, fat, and water
- 10% cheese yield from milk
- More than 1000 varieties of cheese
186
Cheese making
milk -- rennet, acid, acid and heat-->visco-elastic Gel -- variety specific treatments to remove water/whey --> cheese
187
rennet
Enzyme preparation to coagulate milk
188
Rennet source
abomasum of young dairy animals
189
Rennet substitutes
- Bovine pepsin
- Fungal rennets: Rhizomucor miehei, Cryphonectria parasitica
- Vegetable sources
- Fermentation-produced chymosins
190
Coagulation of milk in cheese
...
191
ripened cheeses
- 75% total cheese production
- almost all are enzyme (rennet) coagulated
- acid levels lower (pH higher) then fresh cheeses
- lower moisture levels than fresh cheeses
- ripened or matured by storage (up to 2 years)
192
cheese classification
- Texture (moisture and fat content)
- Method of coagulation (Acid,heat,
rennet)
- Ripened or fresh
- Type of microorganisms (bacteria or mould)
there is a screenshot
193
Basic requirements for cheesemaking: milk pre-treatments
- Good milk quality - low psychrotrophic bacterial count,
low somatic cell count, no antibiotics
- Standardisation (for Cheddar – casein: fat ratio of 0.7:1) to optimise yield and quality
- Pasteurisation 720C/15 sec
- Homogenisation is not normally used for hard cheeses (gives weak curd, softer cheese)
194
Basic requirements for cheesemaking: additives
- Calcium chloride addition (5-20 g/100 kg) to aid coagulation
- Colouring may be added, eg Annatto
- Bacterial starters added - bulk starters, freeze dried - lactic streptococci, lactobacilli, leuconostocs, propionibacteria
- Rennet (chymosin) (ex calf or microbial)
195
CHeese unit operations
- Curd production
- Curd treatment
- Ripening/storage
196
curd production
- Milk pumped to cheese vat avoiding air
- Milk tempered to ~30C
- Starter added and acclimated 30-60min
- CaCl2 added then rennet and milk allowed to set undisturbed (else loss of casein) for approx 30- 40 min
- Cutting - cube size 3-15mm, determines cheese moisture content
- Pre-stirring - “Gentle” stirring just after cutting
- Pre-drainage of whey - allows addition of hot water and removes some lactose form curd
197
Curd treatment
- Cooking - Acid development slowed, Cheese moisture content controlled
- Hot water jacket or Hot water infusion
- Time/temperature program different for various
cheeses (Cheddar 39 degree)
- Final stirring – pH and moisture
- Whey drainage
-Variety specific treatments- “Cheddaring”
198
Cheddar
left to bind together into a curd mass, milled, salted, filled into “hoops”
199
Salting - cheese
0. 5-2%
- Reduce bacterial growth of starter and others
- Moisture changes (water is expelled)
- Smoothens texture by replacing Na for Ca
- Dry salting vs. Brining solutions
- Direct application vs. Infusion
- Moulding/ hooping
- Whey removal, provide texture, shape cheese
- Many mechanized systems exist
200
pressing - cheese
- Type of cheese to be made determines the conditions necessary
- Temperature, relative humidity and time are controlled closely
- Cheddar RH 80%, Temp. 4-8C,and 6-12 months (or more)- Mild 3-6 months old; mature 6-12 months; vintage >12 months
- Cheeses are covered to protect against moisture loss
- mould growth-dipped in wax, vacuum packaging
201
ripening - cheese
Microbiological, chemical, and biochemical process
- Lactose degradation and flavour development
- Protein decomposition and flavour development
- Fat decomposition and flavour development
- Secondary metabolites
202
Cheese ripening
```
screenshotted
Ripening agents in cheese
- Residual rennet
- Indigenous milk enzymes
(i.e., plasmin)
- Starter bacteria
Proteinases, peptidases
other starter enzymes
- Nonstarter lactic acid
bacteria (NSLAB)
Proteinases, peptidases,
other enzymes
- Starter adjuncts, secondary
starter, other microorganisms
```
203
Lactose intolerant people can consume ___ milk
fermented
204
Foam structure
stabilised by present of absorbed protein at fluid interface between gaseous and aqueous phases
205
Main types of protein used to make foam
- egg white protein
- milk protein
there is also plant based milkk foam
206
foamability depends on
protein having capacity for rapid absorption and unfolding at interface
207
foam stability
- refers to relative ability of foam to withstand spontaneous collapse of breakdown from external causes
- dependent on ability of protein to form strong, flexible, cohesive film so as to reduce gas permability and inhibit bubble coalenscence
208
foam stability calculation
(wt. 100ml solution – wt. of liquid drained/ wt. 100ml foam ) * 100
209
Foam formation
- needs gas, water, a surfactant and energy
210
good protein for foamability
B-casein as molecules are flexible, hydrophobic and relaively small
211
dairy foam defined as
structure in which a gaseous phase is stabilized in a matrix in which a significant proportion of the principal components are of milk origin
FOOD2000
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