Dairy Products

milk, cheese (and cheese production), ice cream, 

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Why is milk processed/ heat treated?

  • To destroy/remove any harmful bacteria which will cause rapid spoilage of the milk
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What are the method of heat treating? Describe eac

  • Pasteurisation- short term method (HTST)
    • heating milk lower then boiling point but at a temperature high enough to kill harmful bacteria/organisms and reduce spoilage organisms (99% killed)
    • 72C for 15 seconds
    • 'use by' and stored in a fridge
    • Half vitamin C lost
  • Sterilisation
    • canning at 120C for minutes or hours
    • destroys all microorganisms and spores
    • strong cooked milk flavour
    • colour and flavour change- orangey/ yellow
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What is homogenisation?

  • It is carried out to prevent separation of the cream layer
  • it is essential when milk is subjected to high temperatures
  • warmed to 60C and forced through a small gap in a pressure homogenises (reduces fat droplets)
  • small fat droplets are very stable and doesn't separate out into a cream layer
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Outline the changes in nutritive value of cows mil

  • Vitamin C content is halved
  • 10% thiamine and B12 lost
  • Protein around the fat globules slightly denature causing fat gloubles to stick together and rise to the surface forming a cream layer
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Describe the composition of milk...

  • Varies according to the breed (most important), age, stage of lactation, season, feed
  • Contains Carbohydrates, Lipids and Proteins
  • Milk is an emulsion -> fat in water 
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Describe milk fat...

  • It is saturated fatty acid -> triglyceride
  • held in a suspension (as globules) - fat in water emulsion
  • fresh milk will produce a 'cream layer' on standing where fat globules rise to the surface (homogenisation prevents this)
  • milk is a stable emulsion
  • milk contains a natural emulsifier which is in the protein of milk
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Describe milk proteins...

  • The protein in milk is catergorised into two groups
    • Casein (a curd precipitated by acid or enzyme rennin)
    • Whey (liquid - lactoglubulin and lactalbumin)
  • Casein is a mixture of phosphoproteins -80% of milk - rest from whey
  • Casein is in to parts - a-casein (can be coagulated by calcium), k-casein (insensitive to calcium) 
  • the k-casein surrounds the a-casein
  • k-casein is destroyed by the action of rennin, which then allows calcium to react with a-casein
    • this caused the formation of curd
    • proteins left after this are known as whey
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Describe milk carbohydrate...

  • Consists of the disaccharide lactose
    • formed for glucose and galactose
      • also called milk sugar
  • Absorption of lactose depends on presence of an enzyme lactase
  • the amount of lactase defines the amount of lactose absorbed
    • lactose intolerance
  • curdling and clotting are not the same chemically
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Describe the process of milk souring...

  • milk can sour easily, even when under a chilled condition
    • contains bacteria known as lactic bacilli
      • which brings the breakdown of lactose into lactic acid
  • soured milk pH drops to 5.2 and so the milk curdles 
    • casein is broken down to form curds
  • this happends naturally from lactic acid produces
  • has the same affect when any acid added
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What happens when milk clots?

  • (Rennin is added and the milk is warmed)
  • The enzyme rennin is resposibile for milk clotting
  • It breaks down the k-casein
  • which allows the calcium to react with a-casein
  • this then forms a curd
  • leaving the liquid whey
  • this happens naturally in the stomach and in cheese making
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What are the different fat contents in milk?

Full fat = 3.9%

Semi Skimmed = 1.6%

Skimmed = 0.1%

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What are the vitamins and minerals in milk?

  • Vitamins
    • It contains all the minerals needed for a baby
    • particularly rich in calcium and phosphourus
    • iodine
    • chlorine
    • iron
    • sodium
  • Minerals
    • Vitamin A and D - found in milk fat (very low in skimmed)
    • Vitamin B - riboflavin/ thiamin
    • Vitamin C
    • both thiamin and vitamin C are destroyed by heat treatment
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