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Milk Flashcards

1
Q

Milk is a good source of

A

Calcium and Protein

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2
Q

Inclusion of milk in the diet is associated with

A

reduced prevalence of metabolic syndrome (Elwood, 2007)

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3
Q

UK Adults (19-64) consume

A

136 g/d (NDNS rolling survey 2008-2012)

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4
Q

Composition of Cow’s milk

A

87.5% Water, 3.3% protein, 3.9% Fat, 4.6% Lactose, 0.72% Ash (Kirk and Sawyer, 1991)

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5
Q

Variation of fat - Friesian and Guernsey

A

Friesian = 3.4% Guernsey =4.5%

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6
Q

Name 3 risks of contamination to milk

A

1) Unclean animals, teats, udders, tails
2) Bacterial contmination from infected hands/equipment
3) Chemical contamination from vetinary product residues, cleaning chemicals

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7
Q

Why legislation?

A

To ensure safety and quality of the products

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8
Q

Drinking milk regulations - year and example

A

1976 - nothing can be altered to the composition of drinking milk

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9
Q

Nothing can be altered to the composition of drinking milk

A

Drinking milk regulations 1976

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10
Q

Heat treatment and labelling regulations - year and example - Pasteurisation

A

1973 - Pasteurisation 62.8 - 65.6 degrees for 30 minutes then cooled to below 10 degrees or over 71.7 degrees then cooled to less than 10 degrees

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11
Q

heat treatment and labelling regulations - year and % fat

A

1988 - Skimmed milk no more than 0.3% and semi-skimmed between 1.5-1.8%

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12
Q

Channel island milk must have

A

at least 4% fat

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13
Q

There are standards which outline the appropriate methods to determine the components of milk =

A

BS = British standards and ISO = International organisation of standardisation e.g. BS ISO 15885:2002 Milk Fat. Determination of fatty acid composition by gas-liquid chromatography

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14
Q

European regulations - numbers, title and example

A

Regulation (EC) No (852/853/854)/2004 of the European Parliament and of the council on the hygiene of food stuffs - not allowed to sell raw milk for direct human consumption

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15
Q

What can specific gravity determine?

A

whether adulteration has taken place by adding water/removing cream - adding water lowers the specific gravity and removing cream raises the specific gravity as the specific gravity of fat is 0.93 and the specific gravity of solids-not fat is 1.614 (kirk and sawyer)

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16
Q

How do you measure specific gravity?

A

Lactometer - a form of hydrometer - is used and calibrated to 1.025-1.035 (25.0 degrees - 35 degrees) - it doesn’t determine composition but does determine is adulteration has taken place

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17
Q

How do you stored milk before measuring specific gravity with a lactometer?

A

at 10 degrees for 1-2 hours before testing as chnages in cream on storage

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18
Q

What is a non-destructive way to measure is water or whey has been added to milk?

A

Near-infrared spectroscopy (Kasemsumran)

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19
Q

What are total solids?

A

Constituents of milk that are not water

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20
Q

What is the official method to measure total solids?

A

A gravimetric method - the sample is evaporated in a boiling water bath for 30 mins - then 5g of the sample is placed in the oven at 100 degrees until the moisture/water is evaporated then cooled in a desiccator and weigh - repeat until within 1g

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21
Q

How do you use Richmond’s formula to calculate total solids

A

By using fat determind by the gerber method and a BS density hydrometer reading at 20 degrees

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22
Q

What is Richmond’s formula

A

T% = 0.25 D + 1.22 F + 0.72 (D = hydrometer reading and F= Fat %)

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23
Q

What is the FA comp of milk roughly?

A

15% monounsaturated and 1.5 poly and the rest saturated (Swaisgood, 2008)

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24
Q

What is the accurate reference method to determine total fat?

A

Rose-Gottlieb = a gravimetric method where 10g of milk is mixed with 1ml NH3 solution - casein is solubilised with ethanol and ammonium hydroxide - the fat is extracted twice with ether - distill the ether and cool and weigh

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25
What is another way to measure total fat
Gerber test - milk serum is mixed with concentrated H2SO4 which digests the milk but not the fat - it is then cnetrifuged and the fat collects in the calibrated tube of a butyrometer - amyl alcohol is added to prevent the charring of the fat by the strong acid and to get a clear fat column - it is then transferred to a water bath at 65 degrees and the fat level is read off
26
Why not measure fat with soxhlet
Can't as it is liquid
27
What method to use to determine fatty acid composition
Gas chromatography - (Collomb et al, 2002) used GC to see the differences in fatty acid composition of cows in lowland, mountains and highlands of Switzerland - the biggest difference was with the essential fatty acid C18:2 c9t11 - which increased with altitude - could be used to determine location of mountain cheese that have protected designated origin - however GC is time -consuming, expensive reagents and need qualified staff
28
Name 3 methods to determine protein content
Kjeldahl, formal titration and dye binding
29
Proteins in milk are
Casein (80%) which is found bound to calcium phosphate as a casein micelle and whey (20%)
30
Kjeldahl method for protein:
determines total protein content by determining nitrogen content of the sample and then multiplying by a conversion factor - for milk this is 6.38 - however this does include non- protein nitrogen
31
Formal titration for protein:
mix fresh milk with formaldehyde which makes a free acid (which can be titrated with alkali) then multiply by a factor related to the ratio of casein:albumin
32
Name two dye binding method to determine protein
Lowry and Bradford
33
Describe the Lowry/Bradford dye binding method to determine protein content
Dye binds with polar groups of proteins of opposite ionic charge - the insoluble complex is then removed by centrifugation or filtration and the concentration of unbound dye is assessed from a spectrophotometric curve (dyes= amido black or Orange G - however dye binding has now been replaced by infrared)
34
What can infrared be used to determine in milk
Laporte et al, 1999 - used near-infrared to determine total, fat, total protein and casein content in milk
35
What is lactose
It is a dissaccharide sugar that is comprised of D-glucose and D-glactose - it reduces Fehlings solution forming cuprous oxide
36
How do you measure lactose?
Optically - remove protein and lactose has a specific rotation at 52.53, Gravimetrically - with Fehlings solutions
37
How do you measure ash?
Put sample in a muffle furnace at 500 degress to give oxides of metals - chlorides are not volatised - lower values of ash in the summer than winter - colostrum (first milk) which is high in antibodies is also higher in calcium - ash content is 1.2% whereas normal milk = 0.7%
38
How can you check for mastitis?
Chloride content of normal milk is 3% = mastitis)
39
How do you calculate the casein number - what does this mean?
(Casein N%/Total N%) x 100 <80 = mastitis cows - cows with mastitis may have antibiotic residues in the milk
40
How can you measure acidity - what is normal pH?
by titrating with alkali - normal pH = 6.5-6.7 soured milk=6.3
41
How can you measure for adulteration in addition to lactometer which measures specific gravity?
Hortvet method - standardise thermometer with distilled water and sucrose solution, pour 45ml into freezing tube. stir. note freezing point to 0.001 degrees another similar method to hortvet is the thermistor cryoscope - a different volume and temp measuring device
42
How to calculate the proportion of added water? (adulteration)
if the acidity develops between 0.18-0.30% lactic acid the FPD (corrected) = FPD (determined)- 340 (% lactic acid -0.18) Extraneous water (%) = FPDm (Freezing point depression of genuine milk) - FPDs (of the sample) divided by the FPDm x (100- total solids)
43
Preservatives:
Not allowed in milk - boric acid or formaldehyde maybe present or benzoic acid
44
How to test to ensure pasteurisation has taken place?
Phosphatase test - thermal resistance of phosphatase is greater than pathogens e.g. tubercle bacili - disodium p-nitrophenyl phosphate + milk --> p-nitophenol (yellow colour is produced if the milk contains phosphatase - ie not been pasteurised correctly
45
Plate count can be used to determine bacterial quality but what method is better:
methylene blue reduction test as it is more rapid and more reproducible - bacteria reduces O2 which lowers the oxidation-reduction potential of a dye milk mixture and the colour changes from blue to colourless - milk is okay if it stays blue
46
Cream regulations
1970 - states the minimum fat contents for creams - clotted cream must be 55% fat - double 48% and single 18%
47
Additives are allowed in cream such as stabiliser, thickeners and sugars - how do you test for thickeners?
Gelatine can be detected with the stokes test and sucrose can be detected by Cayeux's text
48
How do you calculate the overrun of cream
(Weight of fluid cream-weight of whipped cream )/(wt of whipped cream) x 100 = Overrun % (100-125% is satisfactory)
49
Describe the feathering test for cream
Pipetter 9ml coffee in 6 tubes, add increasing amounts of citric acid 0.1-0.5ml - heat tubes - add 1ml cream - obsrve feathering or curdling
50
How is cheese produced
from curd produced from the coagulation of souring milk by rennin an enzyme obtained from the inner lining of the forth stomach of the calf
51
Cheese legislation
states maximum limit for water and minimum limit for fat
52
Cheese preservatives
Preservatives that are permitted are Nisin and Sorbic acid up to 1000mg/kg, sodium nitrate up to 100mg/kg and sodium nitrite up to 10mg/kg – not in cheddar or Cheshire cheese - nitrate can be detected with spectrophotometric methods
53
How to use Richmond's formula to calculate the proportion of fat in the dry matter
Richmond’s formula: (100 F)/(35.4 P+F)+0.25 | F = % Fat, P = % Protein
54
Butter Legislation
1966 - Butter should not contain less than 80% milk fat and not more than 2% milk solids other than fat and not more than 16% water
55
Butter composition
Fat 80-84%, water 16%, salt 0.03-1.8% Milk solids not fat 1%
56
How do you calculate water content of butter
oven drying method 100 degrees
57
How do you caluclate salt
volhard method - unsalted butter must be less than 0.1% NaCl
58
How do you measure curd protein
kjeldahl N x 6.38
59
Measure lactose in butter by
Lane-eynon titration
60
Measure fat in butter by
difference Fat% = 100 - water % - salt % - % curd - or use gerber method
61
How do you test for boric acid - a preservative
turmeric test
62
How do you know if it have been adulterated with other fat?
RPK value (Reichert, Polenske, Kirschner) each fat has different ratio can determine changes can also use GC to determine specific fatty acids e.g. C12:C10 is 1:1 for butterfat but >8 for margarine

BMS 3071 (4 decks)

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