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FOOD2000 > Dairy revision and past exam questions > Flashcards

Dairy revision and past exam questions Flashcards

1
Q

caseins and whey products in milk differ in their?

A

solubility at pH 4.6
particle size
rennet coagulability
heat stability

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2
Q

the largest (by size) particles in raw whole milk are

A

fat globules

followed by casein->whey->llactose and salt

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3
Q

pasteurisation of milk is designed to

A

destroy pathogenic and spoilage bacteria in milk

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4
Q

comparing UHT to in-container sterilisation

A

UHT

  • less quality loss
  • more even heating
  • shorter heating time and cooling times

In-container sterilisation

  • less difficulty with particulates
  • greater shelf life
  • more severe heat treatment
  • slows heat penetration
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5
Q

during butter making butter grains are plasticised or ‘worked’ to

A

break up embedded pockets of buttermilk or water in droplets

form larger fat crystals
rupture milk fat globule membrane
impove shelf life
whip the cream?

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6
Q

butter suffers from lack of spreadability at refridgeration temp due to ?

A

it has a high melting temperature due to the high melting temperature of the FA found in largest proportions
The small water droplets prevent growth of bacteria; poorly ‘worked’ butter has an uneven distribution and uneven sizes of water droplets which allow bacterial growth

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7
Q

the role of emulsifier in developing proper ice cream structure is to?

A
  • replace proteins on the surface of milk fat globule
  • reduce stability of milk fat globules
  • make milk fat globule more prone to coalescence during whipping
  • help in flocculation of milk fat globules
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8
Q

high temp heat treatment of milk during yogurt manufacture helps in

A

producing a relatively sterile environment for starter culture growth
denaturing whey proteins
decreasing syneresis from yogurt
shortening coagulation time

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9
Q

TRUE OR FALSE

changes in freezing point of milk can indicate its adulteration with water

A

true

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10
Q

TRUE OR FALSE

the major function of the milk fat globule membrane is dispersion of fat in the aquesous phase of milk

A

true

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11
Q

TRUE OR FALSE

milk contains high levels of poly unsat fat

A

false

- low levels

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12
Q

TRUE OR FALSE

casein micelles are stabilised by k-casein on their surface

A

true

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13
Q

TRUE OR FALSE

the shelf life of ESL milk is as long as UHT milk

A

false
low to high shelf life
pasteurisation milk ->ESL milk->UHT milk

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14
Q

TRUE OR FALSE

cream is a water-in-oil emilsion

A

false is a oil-in-water

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15
Q

TRUE OR FALSE

alkaline phosphatase enzyme acts as an indication of sufficient pasteurisation during milk processing

A

true

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16
Q

Understand composition of milk

A

low casein and high lactose - cow milk

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17
Q

various factors that affect the composition and yield of milk

A

nutritional factors

non nutritional factors

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18
Q

nutrition factors that affect the composition and yield of milk

A

type and quality of feed

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19
Q

non-nutrition factors that affect the composition and yield of milk

A

breed, location, season, temperature

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20
Q

What is milk fat made of?

A

lipids, milk globules enveloped by membrane;
Triacylglycerols; Diacylglycerols; Monoacylglycerols; Free fatty acids; Phospholipids; Sterols; Carotenoids; Fat-soluble vitamins; Flavour compounds

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21
Q

casein

A
  • 80% or protein in cow milk
  • insoluble at pH 4.6
  • large particle size
  • rennet coagulation
  • high heat stability
22
Q

whey

A
  • 20% of protein in cow milk
  • soluble at pH4.6
  • small particle size
  • no rennet coagulation
  • low heat stability
23
Q

what is the effect of various heat treatments on milk quality

A 
Positive
 - improves milk quality by destroying pathogenic and spoilage bacteria, and enzyme activity present in milk
 - achieves desired shelf life
Negative
 - Nutrients can be lost
 - Product colour change/loss
 - Flavours change/loss.
24
Q

methods of heat treatment

A 
in order of increasing severity
thermisation
pasteurisation
ESL
UHT 
In-can sterilisation
25
Q

thermisation

A

milder
enables longer storage and transport
60-65 degrees for 5-15sec

26
Q

pasteurisation

A

most effective control measure for eliminating pathogens that may be present in raw milk
at least 73 degrees for at least 15sec

27
Q

ESL

A

extends shelf life beyond tradition life by reducing reinfection and maintains quality of product
120-130 degrees for 2-5sec

28
Q

UHT

A

sterilisation of food before packing then filling into presterilised containers in a sterile atmosphere
130-150 degrees for 3-5sec

29
Q

In-container sterilisation

A

sterilization of food while in containers with sterile atmosphere
105-120 degrees for 10-30mins

30
Q

What type of emulsion is cream

A

fat/oil-in-water emulsion

- Oil droplets dispersed in aqueous phase.

31
Q

How is milk fat separated

A

Cream is produced from milk by centrifugal separation; the lighter fat globules rise to the top under centrifugation
Separation of milk yields cream and skim milk

32
Q

How is butter made

A

churning pasteurised cream (40% fat) at cool temperatures (>10 degrees)
churning involved agitation or continuous mixing in tolling barrel (can do by hand by shaking in container)

33
Q

How to get good spreadability of butter

A

For good spreadability, the liquid-to-solid fat ratio should remain fairly constant from refrigeration to room temperature (as in margarine).

34
Q

why ‘ageing’ the cream and working the butter is important for butter quality

A
  • Causes fat in fat globules to liquefy
  • Portion of fat will crystalise when the cream is cooled
  • Fast cooling lots of small crystals, slow cooling fewer but larger crystals
  • Larger crystals = softer butter
35
Q

how emulsifiers help in creating the perfect structure of icecream and stabilize the air in ince cream structure

A
  • helps stabilise structure
  • positive influence on air distribution in icecream during freezing process
  • controls excess churning fo fat during the freezing process
  • competes with casein to be on surface of fat globule (replaces casein as thin layer on top of the fat globule)
36
Q

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

A
  • texture (should be smooth)
  • formulate ice cream properly (sugar considerations and stabiliser: bind free water)
  • freeze the ice cream quickly
  • harden the ice cream rapidly
  • avoid temp flunctuations during storage and distribution
37
Q

How yoghurt is process

A
  1. Fortification of milk to increase milk solids-not-fat
  2. Homogenisation at 50-60 degrees
  3. Heat treatment - 85 degrees/30 min. to 90-95degrees /10-20 min
  4. Cool to 40-45degrees
  5. Add starter cultures
  6. Incubate till firm gel forms (5-7 hours)
  7. Stir (for stirred yogurt) & cool
  8. Add fruit if required
  9. Store/dispatch
38
Q

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

A
  • 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
39
Q

how milk is coagulated during cheese making

A 
three different methods of coagulation
acid ->cottage cheese
heat -> ricotta
rennet - >natural cheese
?
40
Q

What are the major steps in cheese making?

A

acidification, coagulation, separating curds and whey, salting, shaping, and ripening.

41
Q

Differences between fresh and ripened cheeses

A
  1. Unripened cheeses are made by coagulating milk proteins (casein) with acid. Examples include soft cheeses like cream cheese, cottage cheese and Neufchatel.
  2. Ripened cheeses are made by coagulating milk proteins with enzymes (rennet) and culture acids.
    - moisture levels lower
    - acid levels lower
42
Q

Plant-based milk substitutes are

A

water extracts of legumes, oil seeds, cereals, or pseudocereals that resemble cow’s milk in appearance.

43
Q

general outline of plant-based milk process

A

the plant material is either soaked and wet milled or the raw material is dry milled, and the flour is extracted in water afterwards

44
Q

general manufacturing process of plant-based milk

A

raw material -> extraction-> separation - >further product formulation -> homogenisation -> heat treatment ->packaging

45
Q

nutritional properties of milk

A

cow - high in fat, protein and energy
soy, oat, hemp are fortified

only soy milk has values comparable to cows milk protein

46
Q

deficiencies in protein can lead to

A

wide number of ailments including kwashiorkor, stunted growth, muscle wasting, weakened immunity, increased risk of cardiovascular disease, diabetes, cancer, osteoporosis, obesity, and other health-related challenges

47
Q

Calcium function

A
  • vascular contraction and vasodilation
  • muscle function
  • nerve transmission
  • intracellular signaling
  • hormone secretion
48
Q

Foam

A
  • structure stabilized by presence of absorbed protein at fluid interface between gaseous and aqueous phases
  • foamability depends on protein having cpacity for rapid absorption and unfoling at interface
  • stability depends on ability of protein to form strong, flexible cohesive film as to reduce gas permeability an dinhibit bubble coalescence
  • formation requires gas, water surfactant and energy
49
Q

what is the composition of milk

A

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

50
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.

FOOD2000 (5 decks)

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