Dairy Flashcards
What does milk contain
lipids, proteins, salts, carbohydrates and many other miscellaneous constituents
What are the essential nutrients found in milk
Vit A, Vit B12, riboflavin, calcium, potassium, magnesium, zinc, phosphorus, carbohydrate, protein
‘raw’ milk
straight from animal
where is milk made?
What is it made from?
In the mammary gland, in units called alveolus - which consists of secretory cells surrounded by blood vessels.
Lactose, fat and most proteins (casein) formed from substrates carried in the blood, other things are simply filtered from the blood.
400L-800L of blood components needed for 1L of milk
What is the composition of cow’s milk
87% water
9% non-fat solids (SNF)
4% fats
How does the composition of Cow’s milk compare to Humans?
more casein, less lactose.
What affects the composition of milk
nutritional factors (type and quality of feed) and non-nutritional factors (breed, stage of lactation, season and temperature, age, size, milking frequency, disease)
breed- holstein usually used: lower fat, lower protein, lower % solids
lactation- increase in fat and protein w time, decrease in lactose.
High milk production in summer.
What is colostrum
The first milk that a cow produces after calving. yellowish. Slaty liquid- very high serum protein and antibodies.
What is the effect of different milk compositions
Physico-chemical properties, functional properties, pricing of milk (prices based on the milk fat and protein solids )
What are the physical properties of milk
- appearance
- density
- osmotic pressure
- freezing point
- Ph and acidity
- Opacity- due to suspended particles of fat, proteins and certain minerals
colour-white to flight yellow (carotene content) - 1.028-1.033 g/cm3 20degrees C
- isotonic
- -0.512 to -0.59
- fresh milk=6.6-6.8, acidity- 0.13% lactic acid.
What does pH of the milk indicate
important indicator of microbial quality of raw milk- concentration of [H+] ions.
Lipids are soluble in non-polar organic solvents and insoluble in water- How does the milk fat exist?
potential SA
Milk is an oil in water emulsion, the fat exists as small globules or droplets dispersed in the milk serum. Each fat globule is enveloped by a (biological membrane) (the milk fat globule membrane- acts as an emulsifier).
What are the main classes of lipids found in milk?
Triacylglycerols (98.3%): glycerol backbone with 3 FA groups, phospholipids (0.8%)
which FA is unique to milk?
What are the most abundant FA
butyric acid- distinctive odour and taste.
C16 (palmitic), C18 (stearic) and C18:1 (oleic)
proportion of TAG varies with diet and lactation stage.
Why does butter not spread straight from the fridge?
It has a high melting temperature due to the high melting temperature of the FA found in largest proportions
Palmitic 25%- 62C
Oleic acid 30% -14C
stearic- 7% - 70C
What affects the crystallisation and positioning of the milk fat?
The distribution of FA’s over the position in TAG molecule.
Butyric and Caproic mostly 3rd
stearic mostly 1st.
What is milk fat
A mixture of different FA and glycerol= TAG
Milk fat globule membrane
- comes from?
- colour
- function
- plasma membrane of the mammary secretory cell
- reddish brown due to xanthine oxidase
- dispersion of fat in the aqueous phase of milk + fat protection from lipase.
what are the minor lipid components found in milk?
Sterols (95% is cholesterol), carotenoids (beta carotene is 95%), fat soluble vitamins (vit A, E, D and K)
What are the types of Milk proteins found in milk?
two major: caseins (~80%) and whey (~20%) proteins.
minor: membrane proteins
How does Casein exist in milk
exist as colloidal particles (casein micelles)
major and minor types of casein found in milk
major: alpha s1,alpha s2, beta and k-caseins (in approximate
ratio of 40:10:35:12); synthesized in secretory cells
minor: gamma and proteose peptone.
insoluble at pH 4.6 and 20C
How does casein exist in milk
Primarily as casein micelles stabilised by k-casein on surface
What stabilises the casein micelle?
Zeta surface potential, -20mV and steric stabilisation.
What is lactoferrin
A minor component of whey, equivalent to transferrin in blood. has antimicrobial properties. Binds iron. heat sensitive: denatures at about 65C.
What is Lactose
It is the carbohydrate in milk. It is a disaccharide made from glucose and galactose. It is the leat soluble of the common sugars.
What is a problem with lactose in the milk
It can cause defects in concentrated milk and frozen dairy products
What are the minerals found in milk
calcium, magnesium, potassium and sodium.
bicarbonate, chloride, citrate slats.
these are distributed between the soluble phase and colloidal phase. - minerals affect stability of milk and milk products + maintain osmotic P.
Importance of cooling milk?
Milk leaves the udder at a temperature of around 37C, it is continuously contaminated with microbes which start to multiply (ideal environment). The cooling the temperature of the milk the slower the rate of bacteria multiplication. Thus milk must be cooled to 4C immediately after milking. (must be transported under refrigerated conditions).
How is milk prepared for processing?
The Raw milk undergoes quality testing via: taste, smell , composition, antibiotics testing, freezing point, pH/ acidity.
How is milk standardised?
though fat and protein- adding or removing
How is milk fat separated out
In commercial dairy plants- uses centrifugal force.
How is milk protein separated out
Commercial dairy plants- membrane filtration (porous polymeric sheets).
definition of permeate
the filtrate- liquid passing though
definition of retentate
the concentrate, the retained liquid.
Different membrane processes in dairy industry
Reverse osmosis (concentration of solutions be removal of water),
nano filtration (concentration of organic components by removal of part of monovalent ions like sodium and chlorine)
Ultrafiltration: concentration of large and macro molecules (e.g. proteins)
micro filtration: removal of bacteria, separation of macro molecules
Dead-end filtration Vs cross flow filtration
dead end filtration= with gravity, on membrane. feed perpendicular to membrane
cross flow= feed parallel to membrane
What is permeate, why is it added?
All components of milk but protein in ultra filtration.
Added to ensure there is specific [] of proteins.
What is the purpose of homogenisation
Ensures that the fat stays evenly distributed though the milk. - Stabilising the fat against gravity separation- primarily causes disruption of fat globules into much smaller ones.
How does Homogenisation occur
Milk is forced though a small passage at high velocity. Breaks down the fat molecules into smaller pieces.
Advantages of Homogenisation (5)
- smaller fat globules leading to less cream- line formation
- whiter and more appetising colour
- reduced sensitivity to fat oxidation
- more full bodied flavour, and better mouthfeel
- better stability of cultured milk products
Disadvantages of homogenisation (2)
- somewhat increased sensitivity to light- sunlight and fluorescent tubes- can results in
‘sunlight flavour’ - the milk might be less suitable for production of semi-hard- hard cheese because the coagulum will be soft and difficult to dewater.
Purpose of heat processing of milk
- To destroy pathogenic and spoilage bacteria in milk.
- main bacteria when it first leaves udder is LA bacteria. during cold storage LAB do not grow but psychrotrophic bacteria do. These are main cause of spoilage (main type: Pseudomonas species)
- Reduce/ destroy enzyme activity present in milk
- Achieve desired shelf-life
Primary bacteria when milk first leave the udder?
lactic acid bacteria e.g. Lactococcus, lactobacillus
What bacteria grows in the cold?
psychrotrophic bacteria
What are the major cause of spoilage in milk
Psychrotrophs
main: Pseudomonas species.
What is spoilage in milk caused by
By enzymes produced by bacteria including protease, lipase, lactase (beta- galactosidase)
If not properly treated, what can occur?
An overgrowth of Psychrotrophs, lead to milkborne diseases such as turberculosis, brucellosis, and typhoid fever.
What heat treatment produces the longest shelf life? long long
UHT, months - can be kept at room temperature
How long can Pasteurized milk last
Days- must be chilled
How long can ESL milk last
Weeks- must be chilled
What are the five types of heat treatment of milk, in order of increasing severity?
- thermisation
- Pasteurisation
- High temperature Pasteurisation (ESL- extended shelf life)
- Ultra high temperature (UHT)
- In container sterilisation
What are some undesirable effects of heating milk
Loosing nutrients, change in colour, change/ loss in flavour
What is thermisation
60-65 degrees for 5-15 seconds
- reduces psychrotrophic bacterial count.
- Does not ensure destruction of pathogenic bacteria
- Not widely practised in Aus
What is Pasteurisation
The most effective control measure for eliminating pathogens that may be present in raw milk, including Lsteria monocytogens, Campylobacter spp., Salmonella spp., and pathogenic E.Coli.
- Most common heat process
- Shelf life can be 7,10, 14 or up to 16 days.
What are the pasteurisation regulations in Australia
Milk must be pasteurised by
(a) heating to a temp of no less then 72C and retaining for no less then 15seconds
(b) heating, using any other time and temperature combination of equivalent or greater lethal effect on any pathogenic micro-organisms in the milk.
What is a test that ensures that milk is properly pasteurised and safe for human consumption?
Alkaline phosphatase test. inactivated under the same conditions.
What are the two processes with equivalent sets of heating conditions
- Batch: Low temp, long time: 65degrees for 15 minutes
* continuous: high temperature, short time
What are the two processes with equivalent sets of heating conditions
- Batch: Low temp, long time: 65degrees for 15 minutes
* continuous: high temperature, short time. 72degrees C for 15 seconds.
What does batch method of pasteurisation involve
Uses a vat pasteurizer.
- consists of a jacketed vat
- surrounded by either circulating water, steam or heating coils or water or steam
- milk is heated and held throughout the holding period while being agitated
- milk may be cooled in the vat.
What does Continuous milk pasteurisation involve
High temp, short time.
uses plate heat exchanger.
* a stack of corrugated stainless steel plates clamped together in a frame.
*the heating medium: vacuum steam or hot water
* hot water on opposite sides of the plates heat milk to a temperature of at least 72degrees C.
* Flows through the holding tube where it is held for at least 16s.
* the warm milk passes through the cooling section where it is cooled to 4C
What is the shelf life of pasteurized milk? why is it not longer
12-16 days
It is not packaged aseptically- spoilage largely due to post-pasteurisation contamination of the milk by psychrotrophic bacteria. (major)
Does not kill some thermoduric organisms such as corynebacteria and the spore-forming bacillus species. (minor spoilage organisms)
What are the advantages of Pasteurisation?
- causes only minor changes to milk components. (little denaturation of whey proteins, very little destruction of vitamins, small loss of water soluble vit, small change in flavour).
- easy to test: using alkaline phosphatase test
- extends shelf life of raw milk
Definition of ESL
‘the ability to extend the shelf life of a chilled distributed product beyond the shelf life of a traditional pasteurised equivalents in a specific market.
limits recontamination faced by pasteurisation
What are the three types of processing technologies for ESL treatment.
Type of technology depends on the type of product and the desired outcome.
1) Pasteurization combined with bactofugation or double bactofugation
2) pasteurization combined with microfiltration
3) high heat treatment
ESL with high heat what are the heating conditions? packaging conditions storage conditions self life? designed to kill?
*heating conditions are between pasteurisation and UHT usually ~120-130 C for 2-5 s
*packaged under very clean but not aseptic conditions
*stored under refrigeration
* shelf life of several weeks- longer than pasteurised.
> not common in AUS
* designed to kill most thermoduric organisms including coryneforms and some sporeforming bacteria such as Bacillus species.
What is Tetra pak ESL?
micro filtration solutions
UHT
heating conditions
Heating conditions 130-150C for 3-5s.
can be stored at room temperature for ~6mthds
what are the main types of UHT processing?
- Direct heating
- milk that is mixed directly with steam, heating by transfer of latent heat from steam
- product held at elevated temp for a shorter period of time= less damage, less cooked flavour - Indirect heating
- milk is heated with heat exchanger: steam or hot water heats a stainless steel barrier which heats the milk.
No direct contact.
Draw the graph of direct and indirect continuous sterilization
- longer amount of time that could be damaged with indirect UHT
What is Direct UHT heating
Direct contact between the steam and the milk to sterilise the milk
steam is converted to water which dilutes the milk- steam must be very good quality.
2 types: steam into milk or milk into steam.
give rapid heating: <1s to reach ~140C.
What is indirect UHT heating
most common in AUS No contact between steam and milk Slower then direct NO dilution causes more flavour changes due to longer heating up and cooling down times
Which form of UHT heating causes more flavour changes? Why?
Indirect UHT heating due to longer heating up and cooling down times.
Changes in milk caused by UHT
Colour Flavour Denaturation of whey proteins Enzymes Vitamin destruction Rennet clotting ability
Changes to colour caused by UHT treatment
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- increase during storage
Changes in flavour caused by UHT
3 major types of flavours: ‘cooked flavour’ - liberation of -SH groups from denatured beta lactoglobulin. decreases during the first few days
‘sterilised flavour’- resulting from maillard reaction -may intensify during storage
‘stale flavour’- from fat oxidation - mainly due to aliphatic aldehydes and methyl ketones
Denaturation in whey proteins caused by UHT
from 60%- 100% denaturation of whey proteins
amount depends on heating regime.
denatured beta-lg links to k-casein on the outside of the casein micelle mainly via disulphide bonds
changes to Enzymes caused by UHT
Most native milk enzymes are inactivated except proteases.
but some bacterial enzymes from psychrotrophic bacterial contaminants of raw milk can survive UHT treatment.
proteases cause age gelation and bitter flavours, lipases cause rancid flavours
effects on vitamin destruction of UHT
No effect on fat-soluble vitamins, small losses of water-soluble vitamins, e.g. thiamine (B1), B6 and B12; folic acid and ascorbic acid (C) reduced also but mainly through oxidation +heat.
vitamin content decreased further during storage
Changes to rennet clotting ability caused by UHT
Clotting rate reduced to half of raw milk, due to interaction of denatured beta-lg and k-casein preventing access of rennet to k-casein
Is UHT milk suitable for making cheese?
nope as it requires rennet action
What type of sterilisation causes the greatest change to milk components
In -container sterilisation
Comparisons between in-container sterilisation and UHT
in container: - slow heat penetration -uneven heating - more severe heat treatment - less difficulty with particulates UHT - shorter heating/ cooling times - more even heating - less quality loss - high temperatures possible - packaging size does not affect processing conditions
How much fat does whole milk contain
~3.4% fat
how much fat does skim milk contain
~0.1% fat
how much more fat is in cream Vs milk
10x
how much more fat is in butter
20x
2x vs cream
What creates the emulsion
The globule membrane
The hydrophilic head (to water)
Hydrophobic tail (to fat)
what type of emulsion is milk fat
an oil in water emulsion
how is cream produced from milk
temperature under which this occurs
By centrifugal separation
the lighter fat globules rise to the top under centrifugation
yields cream and skim milk
38-60C
Why should excess physical handling of raw cream be avoided
because it may rupture the fat globules and cause lipolysis; as well as production of ‘free’ or non-globular fat
How much milk is required for 1L of cream
10L
What does ‘thickened’ table cream often contain
gelatin or vegetable gums
What is the difference between coffee cream and dessert cream
dessert cream has higher viscosity.
coffee cream undergoes two stage high temperature homogenisation- this forms emulsion particles with a fine size and narrow size distribution
dessert cream only undergoes a low temperature single stage homogenisation that promotes cluster; high viscosity.
What type of emulsion is butter
A water in oil emulsion - >80% milk fat
containing water in the form of tiny droplets
fat is the ‘continuous phase’ and water in the form of small droplets is the ‘discontinuous phase’
what vitamins does butter contain
fat soluble- Vit A, D and E
How is butter made
made by ‘churning’ pasteurised cream at cool temperatures –> cream is stored cold for at least 4 hours (generally 12-15h) at ~5C (ageing) before churning to induce growth of some fat crystals and facilitate churning (agitation/ whipping)
What are the categories of butter
usually divided into two main categories:
- sweet cream butter
- cultured or sour cream butter made from bacteriologically soured cream
+ can also be classified according to salt content
- unsalted
- salted
- extra salted
Why is butter aged
To give the fat the required crystalline structure.
ageing takes 12-15hours.
(gives time for the fat globules after pasteurisation to crystallise)
What dictates the softness of the butter
The size of the crystals
the larger the crystals the softer the butter
impacted by the cooling speed
rapid= crystals will be many and small
fast= less but bigger crystals
What does the process of churning do?
first turns the butter into ‘whipped cream’–> then fat globule membrane ruptures–> form butter ‘grains’ (called ‘breaking’ or ‘phase inversion’) + buttermilk –> buttermilk drained off–> butter grains are worked or plasticised into a continuous fatty mass and to break up embedded pockets of buttermilk or water into tiny droplets
Phase inversion
refers to the change from a fat in water emulsion to a water in fat emulsion
What is buttermilk
skim milk plus milk fat globule membrane material
What is ripened butter
Made from cream cultured with lactice acid bacteria which produce diacetyl and lactic acid; has reduced pH due to lactic acid (often unsalted)
cream ripened to pH 5.5 at 21C and then pH 4.6 at 13C
Where is the salt contained in the butter
In the water droplets
Structure of butter
moisture droplets- containing SNF and salt
fat globules- partially crystalline
non-globular fat in continuous phase
fat crystals, semi continuos networks
What determines the category of ice cream
fat content
what must the fat content of ice cream be above to quantify as ‘ice cream’
Above 9% (below called milk ice) - 12-13% (often categorised as either luxury or premium.
Summary of steps in ice cream manufacture
Mix preparation pasteurisation homogenisation chilling aging soft freezing (flavour/ fruit addition) hardening storage
Purpose of the fat in ice cream
up to about 10-15% of ice cream
gives creaminess and improves melting resistance by stabilising the air cell structure of the ice cream
purpose of MSNF in ice cream
helps to stabilize the structure of ice cream due to it’s 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
Purpose of sweeteners in 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 sweetners such as aspartame, acesulfame K, sucralose (in sugar free)
Purpose of stabilisers in ice cream mix
increase the viscosity of the mix and create body and texture
control the growth of the ice crystals
Purpose of Emulsifiers in ice cream mix
helps with freezing
When is chocolate flavour added to the ice-cream mix
before pasteurisation as it often contains undesirable bacteria.
Purpose of the chilling and ageing of ice cream
4-24 hours at depending on stabiliser used
allows time for the fat to cool down and crystallise and for the proteins and polysaccharides to fully hydrate and stabiliser get formation.
What does homogenisation stage of ice cream making achieve?
Reduces size of fat globule
increases surface area
forms membrane
makes possible the use of butter, frozen cream
controls whippibility and churning during the freezing.
How many stages of freezing are there during ice cream making? describe/ compare
Two stages:
soft freeze and hardening
soft freeze only 50% of the water is frozen- during this stage the ice cream is beaten to incorporate air. - rapid freezing. Temperature: -1–9C.
consistency: soft serve
Hardening: 90% of water frozen, its cooled to ~-35C in a blast freezer. Should be as rapid as possible to ensure small ice crystals. must be stored at
What affects ice cream quality
poor storage conditions (freezer temperature, too high or changing).
What is the structure of ice cream
Complex physical structure:
an emulsion of 3 phases: solids (ice crystals, fat, protein, lactose crystals), liquid (unfrozen water), gas (air)
What is essential to the structure of Ice cream?Why?
Emulsifier
Coats the surface of the fat globule in a thin layer- prevents the casein subunits, casein micelle, whey proteins from attaching to the surface of the fat globule this makes the fat globules weaker and thus when beaten the fat globules come together to stabilise the air bubbles
What is overrun (ass with ice cream)
Measure of the amount of air in ice cream. How much the air increases the volume of the mixture.
% overrun= (vol. of ice cream- Vol.of mix used)/ Vol of mix used *100%.
According to Australian food standards, how much food solids must be present in 1L of ice cream
168gm must be present/ L
What affects the shelf life of ice cream
Texture defects is the only consideration- should be smooth.
What are the two main problems that affect the texture of ice cream
- coarseness due to large ice crystals. (slow cooling, fluctuating storage temp)
- sandiness due to lactose crystals- can occur if the lactose: water ratio is >11:1
How to maintain the shelf life of ice cream
- formulate the ice cream properly (sugar considerations, stabilisers: bind free water)
- freeze the ice cream quickly
- Harden the ice cream rapidly
- avoid temperature fluctuations during storage and distribution
What ensures the stability of the casein micelle
2 forces:
- Zeta (surface potential) - net negative charge that repulse each other.
- steric stabilisation: (hairy things on casein, capa casein- dont let caseins come together).
2 forces that repulse the casein micelles from each other.
What is the main starter bacteria used when fermenting dairy products
Lactic acid bacteria
How does lactic acid bacteria produce fermented products
lactic acid formed reduces the pH and destabilises the casein micelle and causes thickening/ coagulation
What gets converted into lactic acid by the starter culture? what effect does this have in milk
lactose
By products: dependent on type different by products can be produced (carbon dioxide, acetic acid, diacetyl, acetaldehyde and several other substances)
Has a preservative effect on milk due to the low pH (inhibits the growth of spoilage organisms)
Which population is able to consume fermented dairy products that can’t consume fresh dairy products? Why
Lactose intolerant, because the lactose is already partly broken down by the bacterial enzymes.
How are yogurt and cheeses distinguished?
In yogurt the whey is not removed from the coagulated casein or curd.
What are the main yogurt cultures
Symbiotic blend of Streptococcus and lactobacillus delbrueckii bulgaricus (LB)
They work together. ST grows faster and produces both acid and carbon dioxide which stimulates LB growth. The proteolytic activity of LB produces stimulatory peptides and amino acids for use by ST.
ST drop initial pH to 5
LB drop to 4.5
What is responsible for the formation of typical yogurt flavour and texture?
The symbiotic blend of Streptococcus thermophilus (ST) and lactobacillus deldrueckii bulgaricus (LB)
What are the fundamentals of yogurt making
Need good growth conditions for starter culture, milk must be held at optimum temperature for relevant starter culture, cooled quickly at the end to stop fermentation
What are the processes of yogurt making
- fortification of milk to increase milk solids not-fat
- homogenisation at 50-60C
heat treatment 85C/ 30min to 90-95/10-20 min - cool to 40-45C
- add starter culture
- incubate till firm gel forms (5-7 hours)
- stir (for stirred yogurt)
-cool - store/ dispatch
What is the purpose of fortifying the milk in the yogurt process
improve consistency (viscosity) and flavour of yogurt
What is the importance of heat treatment in the yogurt making process
this step is unique to yogurt manufacture
varies: 85C/30min - 90-95C/10-20min
Produce a relatively sterile and conducive environment for the starter culture, denatures and coagulate whey proteins
- helps formation of casein network
- increases gel firmness and decreases syneresis
- shortens coagulation time, increases pH at which coagulation occurs
What are the different types of yogurt
- set: incubated in container; additives such as fruit sink to bottom
- stirred: incubated in tanks: gel disrupted by stirring, pumping, filling; additives well suspended
- drinking type: similar to stirred, but the coagulation is broken down to a liquid
- frozen type: incubated in tanks and frozen like ice cream
- Concentrated: incubated in tanks, concentrated and cooled before being packed
- plain/ natural/ flavoured/ fruit
Two ways of manufacturing frozen yogurt
- either yogurt mixed with ice cream mix
2. or ice cream mix is fermented, before further processing
What do probiotic yogurts contain?
examples
probiotics- e.g. ABC cultures:
L.acidophilus
Bifidobacteria
L.Casei
yogurts slowly produce acid compared to LB and ST so added at same time.
yakult, kefir, koumiss
What is rennet
Enzyme preparation to coagulate milk. made in the abdomen of young dairy animals.
What is added to milk to turn it into cheese
Rennet
Acid
acid +heat
What causes the coagulation of milk to produce cheese
Destabilising of the casein molecules due to the proteolysis (from rennet) –> allows the casein molecules to come together/ aggregate.
What are ripened cheeses? how are they different to other cheeses
Ripened or matured by storage up to 2years.
- lower acid levels than for fresh cheeses
- moisture levels lower than for fresh cheeses
How are cheeses classified
- texture
- method of coagulation
- ripened or fresh
- type of Microorganism
Main two types of cheeses
Ripened vs fresh
What process is not used for hard cheeses
homogenisation- gives weak curd, softer cheese
What does the rennet do to cheese
acts on k-casein to give para kappa casein and glycomacropeptide (casein derived peptide)
destabilises the casein micelle and allows coagulation
the 3 Unit operations of cheese production
curd production
curd treatment
ripening/ storage
What are the basic requirements for cheesemaking
- milk pre-treatments:
- Good quality milk- low psychrotrophic bacterial count, low somatic cell count, no antibiotics.
- standardisation
- pasteurisation 72C/15s
- homogenisation (not for hard cheeses).
- additives
- calcium chloride addition to aid coagulation
- colouring
- bacterial starters (develop acid, breakdown proteins, produce gas and flavours)
- rennet (chymosin)
What aids coagulation
calcium chloride
What is cheese: yogurt -
whey
Curd production steps
milk–> heated–> + starter +cacl2 + rennet–> set–> cutting (determines moisture content)–>stirring and pre-drainage of whey
Curd treatment steps
cooking–> final stirring–> whey drainage–> variety specific treatments
what is ‘cheddaring’
When the curd is left to bind together into a curd mass, milled, salted, filled into ‘hoops’.
How is cheese ‘ripened’
microbiologically, chemically and biochemical process
lactose degradation and flavour development
protein decomposition and flavour development
fat decomposition and flavour development
secondary metabolites
What are the ripening agents in cheese?
residual rennet indigenous milk enzymes starter bacteria nonstarter lactic acid bacteria starter adjucts, secondary starter, other microorganisms
Understand the composition of milk
- 87% water
- 4% milk fat and milk fat globule membrane
- 9% NFS:
- proteins
- enzymes
- over ten essential nutrients (Vit A, Vit B12, riboflavin, calcium, potassium, magnesium, zinc…
Various factors that affect the composition and yield of milk
Nutritional factors - type and quality of feed non-nutritional - breed -stage of lactation: yield declines, fat increases, lactose decreases, protein increases - season and temperature (higher in summer) - age and size - disease - milking frequency
What is milk fat made up of
fat globule enveloped by a biological membrane which acts an an emulsifier
mainly triacylglycerols
What are the major differences between casein and whey proteins
casein (80%) - exists as colloidal particles, not soluble at pH 4.6, yes rennet coagulation, high heat stability, large particle size
whey-(~20%) exist in solution, soluble at pH 4.6, not rennet coagulation, low heat stablity, small particle size
Understand the impact of heat treatment on milk
Pasteurisation- mild changes to milk composition
UHT- lots of changes (colour, flavour, denaturation of whey proteins, enzyme denaturation, vitamin destruction, rennet clotting ability reduced
in container- most severe
What are the functions of pasteurisation treatment
Designed to kill Coxiella burnettli
how do different heat treatments vary in intensity
Therminisation pasteurisation ESL UHT in container
what type of emusion is cream and how is the milk fat seperated
oil in water
centrifugal separation
How is butter made? why aging the cream ‘ working is imp for butter quality?
made by churning pasteurised cream at cool temperatures
controlled cooling of the cream: to give fat the required crystalline structure
fast cooling: many small crystals
gradual: bigger = softer butter.
need to rupture the fat globule membrane- phase inversion
Structure of ice cream
has complex physical structure
3 phase emulsion: solids, liquid, gas.
fat globules on air interface
How emulsifiers help in creating the perfect structure of ice cream and stabilise the air in ice cream structure
reduced stability of the milk fat globules
replace proteins on surface of milk fat globules
make milk fat globule more prone to coalescences during whipping
help in flocculation of milk fat globule.
What are the main considerations in maintaining the self life of ice cream
Texture defects
2 main problems
- coarseness due to large ice crystals ass. with slow cooling/ fluctuations during storage - melting refreezing.
- sandiness due to lactose crystals - lactose: water larger then 11: 1 (too much lactose
How yogurts are processed
Fortification of milk to increase NFS. homogenisation- avoid separation heat treatment (unique to yogurt, 85C/ 30 min- produce a conductive environment for the starter culture, denature and coagulate whey proteins, helps form casein network, increase gel firmness and decreases syneresis (release of whey from gel), shorten coagulation time, increase pH at which coagulation occurs. cool- \+ starter--> incubate & cool
what is the importance of heat treatment of milk for yogurt making
heat treatment (unique to yogurt, 85C/ 30 min- produce a conductive environment for the starter culture, denature and coagulate whey proteins, helps form casein network, increase gel firmness and decreases syneresis (release of whey from gel), shorten coagulation time, increase pH at which coagulation occurs
how milk is coagulated during cheese making
though enzyme preparation– Rennet
get proteolysis of k-casein, destabilising casein –> aggregation (aren’t as stable and repulsed anymore) Ca2+ and temperature causes gelatinisation
what are the major steps in cheese making
- curd production - rennet + starter+ cut
- curd treatment - whey drainage
- ripening/ storage
Differences between fresh and ripened cheeses
Ripened by storage for up to 2 years
acid levels lower (high pH) then fresh cheese
moisture levels lower, rennet coagulated
what are the major steps in cheese making
- curd production - rennet + starter+ cut
- curd treatment - whey drainage, slating, ripening
- ripening/ storage-
Differences between fresh and ripened cheeses
Ripened by storage for up to 2 years
acid levels lower (high pH) then fresh cheese
moisture levels lower, rennet coagulated
