Proteins
Proteins are used for their nutritional value but also for their properties for foams, emulsions, and
gels in foot matrices.
Natural proteins do not really alter viscosity. Only large protein aggregates.
Proteins undergo; raw materialsisolation with isoelectric precipitation or filtration so the big and
small Mw molecules can be separatedmodification for example hydrolysis to obtain hydrolysates
or the Maillard reaction to obtain flavour. The point is that it could be accidental (over processing) or
on purpose pasteurization/ drying, the heat that is used affects proteins and their functionalities.
The heat used for drying is also used for pasteurization. Additional heat to neutralize microbes and
enzymes powder properties (wettability and size mostly).
Proteins from the same source but different batch might have less similarities in functionality than
proteins from different source. So, it has to do with variation depending on methods used in
processing, isolation, modification, source etc.
Protein content=protein g/ 100gr of total dry matter
Protein composition=list of proteins in g/ 100gr of total protein.
We know that salt increases ionic strength and also the pH will alter the charge of the proteins.
Basically, for solubility, when trying to dissolve NaCl and increasing C, the salt will dissolve as much as
it can linearly and then it will reach a plateau in which the remaining NaCl forms crystals. Protein
have a more curved line and they reach a plateau much slower in the form of aggregation. The
aggregation happens mostly at around pI where there is not enough electrostatic repulsion btw
proteins to be soluble and due to hydrophobic interactions.
Aggregation can be caused by heat, enzymes, pH changes, association btw proteins and non-protein
compounds. Heat leads to exposure of the hydrophobic sites of the protein (denaturation) and leads
to association btw the proteins due to hydrophobic attraction.
For whey protein, the minimum solubility around the pI is higher than others. Meaning that whey
creates less aggregates in pI and is more soluble in general.
Debye length= how the charges are screened by ionic strength. Counterion concentration= ionic
strength.
Solubility =g/L
The interactions btw and within proteins here are mostly non-covalent- Van der Waals, electrostatic,
hydrophobic, hydrogen and the only covalent is disulphide bridges.
As we said we can isolate the milk with either isoelectric precipitation or filtration based on the Mw.
We use MF to retain fat globules/ cream (>1000nm), UF to retain casein micelles (50-300nm=2kD-
500kD), NF to retain whey proteins (3-50nm=200D-2kD) and RO for salts and carbs (lactose) (<3nm).
Caseins
Caseins are not one protein. They come from the Latin word for cheese, so they are the proteins that
precipitate in the production of cheese. They are 50-300nm and they are surrounded by k-casein
, (contain carbohydrates). In macro micelles, Ca is present which interact with the phosphate groups
we have added.
Caseins are all modified with phosphorylation. Meaning the non-charged serine parts are
phosphorylated and now have a charge. Caseins are also random coils which mean they do not have
a fixated secondary and tertiary structure because they have too many proline residues which are
responsible for the specific conformation of the backbone that hinders formation of a-helices and b-
sheets. That and their uneven distribution of hydrophobicity makes them form micelles and these
into macro-micelles due to phosphate-calcium bridges.
As we said, you can isolate the proteins with filtration or isoelectric precipitation. In the case of
caseins, they can be precipitated if they get aggregated. That can either happen with rennet or acid.
Now, caseins at the pH of milk (6.7), are considered soluble due to the carbohydrate chain of the
kappa casein which likes water (carbohydrate part), and the electrostatic repulsion. You can add
rennet which introduces the chymosin enzyme which removes the kappa casein and hence the
hydrophilicity (rennet casein).
If not, you can add acid which will drop the pH at around the pI of the protein so it will reduce the
net charge hence decrease repulsion. This is acid casein. Now you cannot use it as aggregates so you
can fix the pH back to 6.7 with the addition of NaOH and KOH. These are called sodium or potassium
caseinates.
Caseins are hard to solubilise in general.
Whey
Just like caseins, they are not just one protein. They are globular. 3-50nm (200D-2kD). Sometimes
lactose can also be removed. Depending on their protein content, they can be WPI (>90%) and WPC
(35-80%). For WPC most of it are non-protein compounds and mainly lactose which makes it more
susceptible to Maillard reactions.
The waste stream of casein.
Gelatin
Collagen extracted with heat from bones and animal skin.
Is fibrous and consists of three polypeptide chains that form a triple helix. Main aa are glycine-x-x
one or both xs are proline which, as said before, does not allow the formation of a-helix or b-sheets.
During heating triple helix unfolds but after cooling down it is restored (thermoreversible gel). Many
polypeptide chains can form them (because the gel is created by formation of junction zones of triple
helices via hydrogen bonds which are heat sensitive, after the heat is removed, they will take their
original structure.
Pea proteins are globular, so they behave more like whey.
Protein Modifications
Proteins need to be modified to remove for example the allergenicity. That can happen with
enzymatic hydrolysis, heat, and spray drying. In hydrolysis, the enzyme will break down the proteins
in its peptides and each peptide will have its own pI, hence their own solubility. You can measure the
Degree of hydrolysis by No of hydrolysed peptide bonds per 1gr of protein/ total peptide bonds per
1gr of protein. You basically calculate the free NH2 (amino groups) because when you break a
