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FOOD2000 > Dairy > Flashcards

Dairy Flashcards

1
Q

What does milk contain

A

lipids, proteins, salts, carbohydrates and many other miscellaneous constituents

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2
Q

What are the essential nutrients found in milk

A

Vit A, Vit B12, riboflavin, calcium, potassium, magnesium, zinc, phosphorus, carbohydrate, protein

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3
Q

‘raw’ milk

A

straight from animal

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4
Q

where is milk made?

What is it made from?

A

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

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5
Q

What is the composition of cow’s milk

A

87% water
9% non-fat solids (SNF)
4% fats

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6
Q

How does the composition of Cow’s milk compare to Humans?

A

more casein, less lactose.

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7
Q

What affects the composition of milk

A

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.

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8
Q

What is colostrum

A

The first milk that a cow produces after calving. yellowish. Slaty liquid- very high serum protein and antibodies.

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9
Q

What is the effect of different milk compositions

A

Physico-chemical properties, functional properties, pricing of milk (prices based on the milk fat and protein solids )

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10
Q

What are the physical properties of milk

  1. appearance
  2. density
  3. osmotic pressure
  4. freezing point
  5. Ph and acidity
A
  1. Opacity- due to suspended particles of fat, proteins and certain minerals
    colour-white to flight yellow (carotene content)
  2. 1.028-1.033 g/cm3 20degrees C
  3. isotonic
  4. -0.512 to -0.59
  5. fresh milk=6.6-6.8, acidity- 0.13% lactic acid.
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11
Q

What does pH of the milk indicate

A

important indicator of microbial quality of raw milk- concentration of [H+] ions.

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12
Q

Lipids are soluble in non-polar organic solvents and insoluble in water- How does the milk fat exist?
potential SA

A

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).

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13
Q

What are the main classes of lipids found in milk?

A

Triacylglycerols (98.3%): glycerol backbone with 3 FA groups, phospholipids (0.8%)

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14
Q

which FA is unique to milk?

What are the most abundant FA

A

butyric acid- distinctive odour and taste.
C16 (palmitic), C18 (stearic) and C18:1 (oleic)
proportion of TAG varies with diet and lactation stage.

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15
Q

Why does butter not spread straight from the fridge?

A

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

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16
Q

What affects the crystallisation and positioning of the milk fat?

A

The distribution of FA’s over the position in TAG molecule.
Butyric and Caproic mostly 3rd
stearic mostly 1st.

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17
Q

What is milk fat

A

A mixture of different FA and glycerol= TAG

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18
Q

Milk fat globule membrane

  • comes from?
  • colour
  • function
A
  • 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.
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19
Q

what are the minor lipid components found in milk?

A

Sterols (95% is cholesterol), carotenoids (beta carotene is 95%), fat soluble vitamins (vit A, E, D and K)

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20
Q

What are the types of Milk proteins found in milk?

A

two major: caseins (~80%) and whey (~20%) proteins.

minor: membrane proteins

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21
Q

How does Casein exist in milk

A

exist as colloidal particles (casein micelles)

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22
Q

major and minor types of casein found in milk

A

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

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23
Q

How does casein exist in milk

A

Primarily as casein micelles stabilised by k-casein on surface

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24
Q

What stabilises the casein micelle?

A

Zeta surface potential, -20mV and steric stabilisation.

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25
Q

What is lactoferrin

A

A minor component of whey, equivalent to transferrin in blood. has antimicrobial properties. Binds iron. heat sensitive: denatures at about 65C.

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26
Q

What is Lactose

A

It is the carbohydrate in milk. It is a disaccharide made from glucose and galactose. It is the leat soluble of the common sugars.

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27
Q

What is a problem with lactose in the milk

A

It can cause defects in concentrated milk and frozen dairy products

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28
Q

What are the minerals found in milk

A

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.

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29
Q

Importance of cooling milk?

A

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).

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30
Q

How is milk prepared for processing?

A

The Raw milk undergoes quality testing via: taste, smell , composition, antibiotics testing, freezing point, pH/ acidity.

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31
Q

How is milk standardised?

A

though fat and protein- adding or removing

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32
Q

How is milk fat separated out

A

In commercial dairy plants- uses centrifugal force.

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33
Q

How is milk protein separated out

A

Commercial dairy plants- membrane filtration (porous polymeric sheets).

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34
Q

definition of permeate

A

the filtrate- liquid passing though

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35
Q

definition of retentate

A

the concentrate, the retained liquid.

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36
Q

Different membrane processes in dairy industry

A

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

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37
Q

Dead-end filtration Vs cross flow filtration

A

dead end filtration= with gravity, on membrane. feed perpendicular to membrane
cross flow= feed parallel to membrane

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38
Q

What is permeate, why is it added?

A

All components of milk but protein in ultra filtration.

Added to ensure there is specific [] of proteins.

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39
Q

What is the purpose of homogenisation

A

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.

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40
Q

How does Homogenisation occur

A

Milk is forced though a small passage at high velocity. Breaks down the fat molecules into smaller pieces.

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41
Q

Advantages of Homogenisation (5)

A
  • 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
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42
Q

Disadvantages of homogenisation (2)

A
  • 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.
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43
Q

Purpose of heat processing of milk

A
  • 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
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44
Q

Primary bacteria when milk first leave the udder?

A

lactic acid bacteria e.g. Lactococcus, lactobacillus

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45
Q

What bacteria grows in the cold?

A

psychrotrophic bacteria

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46
Q

What are the major cause of spoilage in milk

A

Psychrotrophs

main: Pseudomonas species.

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47
Q

What is spoilage in milk caused by

A

By enzymes produced by bacteria including protease, lipase, lactase (beta- galactosidase)

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48
Q

If not properly treated, what can occur?

A

An overgrowth of Psychrotrophs, lead to milkborne diseases such as turberculosis, brucellosis, and typhoid fever.

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49
Q

What heat treatment produces the longest shelf life? long long

A

UHT, months - can be kept at room temperature

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50
Q

How long can Pasteurized milk last

A

Days- must be chilled

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51
Q

How long can ESL milk last

A

Weeks- must be chilled

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52
Q

What are the five types of heat treatment of milk, in order of increasing severity?

A
  1. thermisation
  2. Pasteurisation
  3. High temperature Pasteurisation (ESL- extended shelf life)
  4. Ultra high temperature (UHT)
  5. In container sterilisation
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53
Q

What are some undesirable effects of heating milk

A

Loosing nutrients, change in colour, change/ loss in flavour

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54
Q

What is thermisation

A

60-65 degrees for 5-15 seconds

  • reduces psychrotrophic bacterial count.
  • Does not ensure destruction of pathogenic bacteria
  • Not widely practised in Aus
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55
Q

What is Pasteurisation

A

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.
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56
Q

What are the pasteurisation regulations in Australia

A

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.

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57
Q

What is a test that ensures that milk is properly pasteurised and safe for human consumption?

A

Alkaline phosphatase test. inactivated under the same conditions.

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58
Q

What are the two processes with equivalent sets of heating conditions

A
  • Batch: Low temp, long time: 65degrees for 15 minutes

* continuous: high temperature, short time

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59
Q

What are the two processes with equivalent sets of heating conditions

A
  • Batch: Low temp, long time: 65degrees for 15 minutes

* continuous: high temperature, short time. 72degrees C for 15 seconds.

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60
Q

What does batch method of pasteurisation involve

A

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.
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61
Q

What does Continuous milk pasteurisation involve

A

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

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62
Q

What is the shelf life of pasteurized milk? why is it not longer

A

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)

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63
Q

What are the advantages of Pasteurisation?

A
  • 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
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64
Q

Definition of ESL

A

‘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

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65
Q

What are the three types of processing technologies for ESL treatment.

A

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

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66
Q 
ESL with high heat 
what are the heating conditions?
packaging conditions 
storage conditions 
self life?
designed to kill?
A

*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.

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67
Q

What is Tetra pak ESL?

A

micro filtration solutions

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68
Q

UHT

heating conditions

A

Heating conditions 130-150C for 3-5s.

can be stored at room temperature for ~6mthds

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69
Q

what are the main types of UHT processing?

A
  1. 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
  2. Indirect heating
    - milk is heated with heat exchanger: steam or hot water heats a stainless steel barrier which heats the milk.
    No direct contact.
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70
Q

Draw the graph of direct and indirect continuous sterilization

A
  • longer amount of time that could be damaged with indirect UHT
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71
Q

What is Direct UHT heating

A

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.

72
Q

What is indirect UHT heating

A 
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
73
Q

Which form of UHT heating causes more flavour changes? Why?

A

Indirect UHT heating due to longer heating up and cooling down times.

74
Q

Changes in milk caused by UHT

A 
Colour
Flavour
Denaturation of whey proteins 
Enzymes 
Vitamin destruction
Rennet clotting ability
75
Q

Changes to colour caused by UHT treatment

A

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

76
Q

Changes in flavour caused by UHT

A

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

77
Q

Denaturation in whey proteins caused by UHT

A

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

78
Q

changes to Enzymes caused by UHT

A

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

79
Q

effects on vitamin destruction of UHT

A

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

80
Q

Changes to rennet clotting ability caused by UHT

A

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

81
Q

Is UHT milk suitable for making cheese?

A

nope as it requires rennet action

82
Q

What type of sterilisation causes the greatest change to milk components

A

In -container sterilisation

83
Q

Comparisons between in-container sterilisation and UHT

A 
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
84
Q

How much fat does whole milk contain

A

~3.4% fat

85
Q

how much fat does skim milk contain

A

~0.1% fat

86
Q

how much more fat is in cream Vs milk

A

10x

87
Q

how much more fat is in butter

A

20x

2x vs cream

88
Q

What creates the emulsion

A

The globule membrane
The hydrophilic head (to water)
Hydrophobic tail (to fat)

89
Q

what type of emulsion is milk fat

A

an oil in water emulsion

90
Q

how is cream produced from milk

temperature under which this occurs

A

By centrifugal separation
the lighter fat globules rise to the top under centrifugation
yields cream and skim milk
38-60C

91
Q

Why should excess physical handling of raw cream be avoided

A

because it may rupture the fat globules and cause lipolysis; as well as production of ‘free’ or non-globular fat

92
Q

How much milk is required for 1L of cream

A

10L

93
Q

What does ‘thickened’ table cream often contain

A

gelatin or vegetable gums

94
Q

What is the difference between coffee cream and dessert cream

A

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.

95
Q

What type of emulsion is butter

A

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’

96
Q

what vitamins does butter contain

A

fat soluble- Vit A, D and E

97
Q

How is butter made

A

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)

98
Q

What are the categories of butter

A

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
99
Q

Why is butter aged

A

To give the fat the required crystalline structure.
ageing takes 12-15hours.

(gives time for the fat globules after pasteurisation to crystallise)

100
Q

What dictates the softness of the butter

A

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

101
Q

What does the process of churning do?

A

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

102
Q

Phase inversion

A

refers to the change from a fat in water emulsion to a water in fat emulsion

103
Q

What is buttermilk

A

skim milk plus milk fat globule membrane material

104
Q

What is ripened butter

A

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

105
Q

Where is the salt contained in the butter

A

In the water droplets

106
Q

Structure of butter

A

moisture droplets- containing SNF and salt
fat globules- partially crystalline
non-globular fat in continuous phase
fat crystals, semi continuos networks

107
Q

What determines the category of ice cream

A

fat content

108
Q

what must the fat content of ice cream be above to quantify as ‘ice cream’

A

Above 9% (below called milk ice) - 12-13% (often categorised as either luxury or premium.

109
Q

Summary of steps in ice cream manufacture

A 
Mix preparation 
pasteurisation 
homogenisation 
chilling 
aging 
soft freezing
(flavour/ fruit addition) 
hardening 
storage
110
Q

Purpose of the fat in ice cream

A

up to about 10-15% of ice cream

gives creaminess and improves melting resistance by stabilising the air cell structure of the ice cream

111
Q

purpose of MSNF in ice cream

A

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

112
Q

Purpose of sweeteners in ice cream

A

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)

113
Q

Purpose of stabilisers in ice cream mix

A

increase the viscosity of the mix and create body and texture
control the growth of the ice crystals

114
Q

Purpose of Emulsifiers in ice cream mix

A

helps with freezing

115
Q

When is chocolate flavour added to the ice-cream mix

A

before pasteurisation as it often contains undesirable bacteria.

116
Q

Purpose of the chilling and ageing of ice cream

A

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.

117
Q

What does homogenisation stage of ice cream making achieve?

A

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.

118
Q

How many stages of freezing are there during ice cream making? describe/ compare

A

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

119
Q

What affects ice cream quality

A

poor storage conditions (freezer temperature, too high or changing).

120
Q

What is the structure of ice cream

A

Complex physical structure:

an emulsion of 3 phases: solids (ice crystals, fat, protein, lactose crystals), liquid (unfrozen water), gas (air)

121
Q

What is essential to the structure of Ice cream?Why?

A

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

122
Q

What is overrun (ass with ice cream)

A

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%.

123
Q

According to Australian food standards, how much food solids must be present in 1L of ice cream

A

168gm must be present/ L

124
Q

What affects the shelf life of ice cream

A

Texture defects is the only consideration- should be smooth.

125
Q

What are the two main problems that affect the texture of ice cream

A
  • 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
126
Q

How to maintain the shelf life of ice cream

A
  1. formulate the ice cream properly (sugar considerations, stabilisers: bind free water)
  2. freeze the ice cream quickly
  3. Harden the ice cream rapidly
  4. avoid temperature fluctuations during storage and distribution
127
Q

What ensures the stability of the casein micelle

A

2 forces:

  1. Zeta (surface potential) - net negative charge that repulse each other.
  2. steric stabilisation: (hairy things on casein, capa casein- dont let caseins come together).

2 forces that repulse the casein micelles from each other.

128
Q

What is the main starter bacteria used when fermenting dairy products

A

Lactic acid bacteria

129
Q

How does lactic acid bacteria produce fermented products

A

lactic acid formed reduces the pH and destabilises the casein micelle and causes thickening/ coagulation

130
Q

What gets converted into lactic acid by the starter culture? what effect does this have in milk

A

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)

131
Q

Which population is able to consume fermented dairy products that can’t consume fresh dairy products? Why

A

Lactose intolerant, because the lactose is already partly broken down by the bacterial enzymes.

132
Q

How are yogurt and cheeses distinguished?

A

In yogurt the whey is not removed from the coagulated casein or curd.

133
Q

What are the main yogurt cultures

A

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

134
Q

What is responsible for the formation of typical yogurt flavour and texture?

A

The symbiotic blend of Streptococcus thermophilus (ST) and lactobacillus deldrueckii bulgaricus (LB)

135
Q

What are the fundamentals of yogurt making

A

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

136
Q

What are the processes of yogurt making

A
  • 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
137
Q

What is the purpose of fortifying the milk in the yogurt process

A

improve consistency (viscosity) and flavour of yogurt

138
Q

What is the importance of heat treatment in the yogurt making process

A

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
139
Q

What are the different types of yogurt

A
  • 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
140
Q

Two ways of manufacturing frozen yogurt

A
  1. either yogurt mixed with ice cream mix

2. or ice cream mix is fermented, before further processing

141
Q

What do probiotic yogurts contain?

examples

A

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

142
Q

What is rennet

A

Enzyme preparation to coagulate milk. made in the abdomen of young dairy animals.

143
Q

What is added to milk to turn it into cheese

A

Rennet
Acid
acid +heat

144
Q

What causes the coagulation of milk to produce cheese

A

Destabilising of the casein molecules due to the proteolysis (from rennet) –> allows the casein molecules to come together/ aggregate.

145
Q

What are ripened cheeses? how are they different to other cheeses

A

Ripened or matured by storage up to 2years.

  • lower acid levels than for fresh cheeses
  • moisture levels lower than for fresh cheeses
146
Q

How are cheeses classified

A
  • texture
  • method of coagulation
  • ripened or fresh
  • type of Microorganism
147
Q

Main two types of cheeses

A

Ripened vs fresh

148
Q

What process is not used for hard cheeses

A

homogenisation- gives weak curd, softer cheese

149
Q

What does the rennet do to cheese

A

acts on k-casein to give para kappa casein and glycomacropeptide (casein derived peptide)
destabilises the casein micelle and allows coagulation

150
Q

the 3 Unit operations of cheese production

A

curd production
curd treatment
ripening/ storage

151
Q

What are the basic requirements for cheesemaking

A
  • 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)
152
Q

What aids coagulation

A

calcium chloride

153
Q

What is cheese: yogurt -

A

whey

154
Q

Curd production steps

A

milk–> heated–> + starter +cacl2 + rennet–> set–> cutting (determines moisture content)–>stirring and pre-drainage of whey

155
Q

Curd treatment steps

A

cooking–> final stirring–> whey drainage–> variety specific treatments

156
Q

what is ‘cheddaring’

A

When the curd is left to bind together into a curd mass, milled, salted, filled into ‘hoops’.

157
Q

How is cheese ‘ripened’

A

microbiologically, chemically and biochemical process

lactose degradation and flavour development
protein decomposition and flavour development
fat decomposition and flavour development
secondary metabolites

158
Q

What are the ripening agents in cheese?

A 
residual rennet 
indigenous milk enzymes 
starter bacteria 
nonstarter lactic acid bacteria 
starter adjucts, secondary starter, other 
microorganisms
159
Q

Understand the composition of milk

A
  • 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…
160
Q

Various factors that affect the composition and yield of milk

A 
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
161
Q

What is milk fat made up of

A

fat globule enveloped by a biological membrane which acts an an emulsifier
mainly triacylglycerols

162
Q

What are the major differences between casein and whey proteins

A

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

163
Q

Understand the impact of heat treatment on milk

A

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

164
Q

What are the functions of pasteurisation treatment

A

Designed to kill Coxiella burnettli

165
Q

how do different heat treatments vary in intensity

A 
Therminisation 
pasteurisation 
ESL 
UHT 
in container
166
Q

what type of emusion is cream and how is the milk fat seperated

A

oil in water

centrifugal separation

167
Q

How is butter made? why aging the cream ‘ working is imp for butter quality?

A

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

168
Q

Structure of ice cream

A

has complex physical structure
3 phase emulsion: solids, liquid, gas.

fat globules on air interface

169
Q

How emulsifiers help in creating the perfect structure of ice cream and stabilise the air in ice cream structure

A

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.

170
Q

What are the main considerations in maintaining the self life of ice cream

A

Texture defects

2 main problems

  1. coarseness due to large ice crystals ass. with slow cooling/ fluctuations during storage - melting refreezing.
  2. sandiness due to lactose crystals - lactose: water larger then 11: 1 (too much lactose
171
Q

How yogurts are processed

A 
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 
&amp; cool
172
Q

what is the importance of heat treatment of milk for yogurt making

A

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

173
Q

how milk is coagulated during cheese making

A

though enzyme preparation– Rennet

get proteolysis of k-casein, destabilising casein –> aggregation (aren’t as stable and repulsed anymore) Ca2+ and temperature causes gelatinisation

174
Q

what are the major steps in cheese making

A
  1. curd production - rennet + starter+ cut
  2. curd treatment - whey drainage
  3. ripening/ storage
175
Q

Differences between fresh and ripened cheeses

A

Ripened by storage for up to 2 years
acid levels lower (high pH) then fresh cheese
moisture levels lower, rennet coagulated

176
Q

what are the major steps in cheese making

A
  1. curd production - rennet + starter+ cut
  2. curd treatment - whey drainage, slating, ripening
  3. ripening/ storage-
177
Q

Differences between fresh and ripened cheeses

A

Ripened by storage for up to 2 years
acid levels lower (high pH) then fresh cheese
moisture levels lower, rennet coagulated

FOOD2000 (5 decks)

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