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BMS 3071 > Milk > Flashcards

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
Q

What is another way to measure total fat

A

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
Q

Why not measure fat with soxhlet

A

Can’t as it is liquid

27
Q

What method to use to determine fatty acid composition

A

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
Q

Name 3 methods to determine protein content

A

Kjeldahl, formal titration and dye binding

29
Q

Proteins in milk are

A

Casein (80%) which is found bound to calcium phosphate as a casein micelle and whey (20%)

30
Q

Kjeldahl method for protein:

A

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
Q

Formal titration for protein:

A

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
Q

Name two dye binding method to determine protein

A

Lowry and Bradford

33
Q

Describe the Lowry/Bradford dye binding method to determine protein content

A

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
Q

What can infrared be used to determine in milk

A

Laporte et al, 1999 - used near-infrared to determine total, fat, total protein and casein content in milk

35
Q

What is lactose

A

It is a dissaccharide sugar that is comprised of D-glucose and D-glactose - it reduces Fehlings solution forming cuprous oxide

36
Q

How do you measure lactose?

A

Optically - remove protein and lactose has a specific rotation at 52.53, Gravimetrically - with Fehlings solutions

37
Q

How do you measure ash?

A

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
Q

How can you check for mastitis?

A

Chloride content of normal milk is 3% = mastitis)

39
Q

How do you calculate the casein number - what does this mean?

A

(Casein N%/Total N%) x 100 <80 = mastitis cows - cows with mastitis may have antibiotic residues in the milk

40
Q

How can you measure acidity - what is normal pH?

A

by titrating with alkali - normal pH = 6.5-6.7 soured milk=6.3

41
Q

How can you measure for adulteration in addition to lactometer which measures specific gravity?

A

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
Q

How to calculate the proportion of added water? (adulteration)

A

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
Q

Preservatives:

A

Not allowed in milk - boric acid or formaldehyde maybe present or benzoic acid

44
Q

How to test to ensure pasteurisation has taken place?

A

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
Q

Plate count can be used to determine bacterial quality but what method is better:

A

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
Q

Cream regulations

A

1970 - states the minimum fat contents for creams - clotted cream must be 55% fat - double 48% and single 18%

47
Q

Additives are allowed in cream such as stabiliser, thickeners and sugars - how do you test for thickeners?

A

Gelatine can be detected with the stokes test and sucrose can be detected by Cayeux’s text

48
Q

How do you calculate the overrun of cream

A

(Weight of fluid cream-weight of whipped cream )/(wt of whipped cream) x 100 = Overrun % (100-125% is satisfactory)

49
Q

Describe the feathering test for cream

A

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
Q

How is cheese produced

A

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
Q

Cheese legislation

A

states maximum limit for water and minimum limit for fat

52
Q

Cheese preservatives

A

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
Q

How to use Richmond’s formula to calculate the proportion of fat in the dry matter

A

Richmond’s formula: (100 F)/(35.4 P+F)+0.25

F = % Fat, P = % Protein

54
Q

Butter Legislation

A

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
Q

Butter composition

A

Fat 80-84%, water 16%, salt 0.03-1.8% Milk solids not fat 1%

56
Q

How do you calculate water content of butter

A

oven drying method 100 degrees

57
Q

How do you caluclate salt

A

volhard method - unsalted butter must be less than 0.1% NaCl

58
Q

How do you measure curd protein

A

kjeldahl N x 6.38

59
Q

Measure lactose in butter by

A

Lane-eynon titration

60
Q

Measure fat in butter by

A

difference Fat% = 100 - water % - salt % - % curd - or use gerber method

61
Q

How do you test for boric acid - a preservative

A

turmeric test

62
Q

How do you know if it have been adulterated with other fat?

A

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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