Milk Proteins Flashcards
What are the three phases of milk and what are they each comprised of?
- Stable emulsion = microorganisms and fat globules
- Colloidal suspension = caseins and whey proteins
- True solution = lactose, water, soluble minerals and non-protein nitrogen
What are caseins composed of and in what ratio?
Alpha : beta : kappa
50 : 40 : 10
What are alpha and beta caseins?
Phosphoproteins = conjugated proteins containing the amino acids phosphoserine
What are kappa caseins?
Glycoproteins = more hydrophilic
What do caseins self assemble into?
Micelles = proteins packets
How are alpha and beta caseins held together in micelles?
Hydrophobic interactions
Where are kappa caseins found in micelles and why?
On the surface to allow for suspension in milk
What forces do kappa caseins provide between micelles?
Repulsive steric forces
What compound are micelles in close association with and what property does the compound result in milk having?
Calcium phosphate
Results in milk being white
What are the importance of caseins?
- Dominant protein in bovine milk
- Carry significant amounts of calcium phosphate
- Can be separated easily to produce functional ingredients
How is the separation of casein components from skimmed milk achieved?
By precipitation of membrane processing
What does the separation of casein produce and why is it in this form?
Casein based ingredients in powder form so that they do not spoil
What are the six main casein based ingredients produced by the separation of caseins?
- Skimmed milk powder
- Acid caseins
- Rennet caseins
- Caseinates
- Milk protein concentrates
- Phosphocaseins
Does the production of SMP require major separation processes?
No - except the removal of fat by centrifugation
How is SMP produced?
- Skimmed milk is pasteurized
- Heat induced denaturation of whey proteins attached to micelles occurs
- Samples are evaporated and spray dried to produce a powder
What percentage of SMP is protein, and of that protein what percentage are caseins?
35% protein
80% caseins
Is SMP soluble?
Yes
What can SMP be further processed to produce?
UHT milk
What are acid caseins produced in preparation for?
Yoghurt production
How are acid caseins produced?
- Caseins self-aggregate as a result of changing the pH of skimmed milk (from 6.7 to 4.6)
- Caseins remain in the curd
- Other compounds are eliminated as they are soluble at low pH
- Water washing
- Pasteurising
- Drying
What might be used to lower the pH during acid casein production?
Hydrochloric acid
Sulphuric acid
Lactobacillus
What are rennet caseins produced in preparation for?
Cheese production
How are rennet caseins produced?
- Caseins self aggregate due to the action of chymosin (rennet)
- Curd and whey are formed
- Calcium is recovered
- Treatment of curd is similar to the production of acid caseins
Are dried rennet caseins soluble in water?
No
What is the most efficient way of producing high casein ingredients?
Rennet casein production
How are caseinates produced?
- Acid or rennet caseins are neutralised through alkali addition
- The change in pH converts insoluble acid caseins into casein dispersions = recovering their solubility
If pH is increased using sodium hydroxide in caseinate production what type of caseinate is produced?
Sodium caseinate
If pH is increased using calcium hydroxide in caseinate production what type of caseinate is produced?
Calcium caseinate
How are milk protein concentrates produced?
By the concentration of caseins by membrane technology
What do milk protein concentrates contain?
Caseins and whey proteins
Low lactose concentration
Significant amount of calcium phosphate
Why do milk protein concentrates contain an significant amount of calcium phosphate?
Because caseins form micelles
What are milk protein concentrates used for?
For fortifying beverages
How are phosphocaseins produced?
By microfiltration
What do phosphocaseins contain?
Only casein micelles with attached calcium phosphate
What percentage of phosphcasein powder is protein?
75-80%
When might rehydration of phosphcaseins be possible?
If they are not heated above 50 degrees
What are the uses and applications of casein based ingredients?
Acid gels Recombined milk Food emulsions Cheese analogue Chocolate Bakery
What do acid gels do and what casein based ingredients are involved in producing them?
Control gel behaviour during fermentation by bacterial cultures (to produce yoghurt and cream cheese)
- Caseinates
- Phophocaseins
- SMP
What casein based ingredient is involved in producing recombined milk and why?
SMP because it is stable at high temperatures
What casein based ingredients are used in food emulsions?
Sodium caseinate = protein emulsifier
Calcium caseinate and SMP = oil in water emulsions
SMP = water in oil emulsions
What casein based ingredient is involved in producing cheese analogue?
Rennet Casein
What casein based ingredients are involved in producing chocolate?
SMP and whey powders
What casein based ingredient is involved in bakery?
SMP
What is whey?
A byproduct of the manufacturing of dairy products
What is whey comprised of?
- Beta-lactoglobulins
- Alpha-lactalbumins
- Glycomacropeptides
- Immunoglobulins
- Serum albumins
- Lactoferrin and lactoperoxidase
What is a property of beta-lactoglobulin?
High proportion of hydrophobic residues
What do alpha-lactalbumins form?
Parts of lactose synthase enzymes
What are glycomacropeptides?
Glycopeptides derived from caseins
What are immunoglobulins?
Heat sensitive globular proteins from blood
What do serum albumins contain and how do they affect serum albumins interactions?
A large number of disulphide bridges which react with beta-lactoglobulins
Name three whey protein ingredients.
Whey protein concentrates
Whey protein isolates
Whey hydrolysates
How are whey protein concentrates obtained?
By ultrafiltration
What might be lost during ultrafiltration of whey?
Alpha-lactalbumins
How are whey protein isolates obtained?
By ion exchange separation
How are whey hydrolysates obtained?
Protein hydrolysis - incubating proteins with proteolytic enzymes at elevated temperatures
What considerations should be taken into account during the manufacturing of whey based ingredients?
Effect of heat treatment
Changes during storage
Flavour of whey hydrolysates (hydrophobic peptides produce a bitter taste)
What are the functional uses of whey proteins?
Solubilizers
Gelation
Foaming
Emulsification
What are the non functional uses of whey proteins?
Infant formulations Sports nutrition (drinks and bars)
