Production of protein isolates

Question 1

ISOLATION OF PROTEINS: general scheme

Answer 1

1. Plant or animal material –> grinding extraction centrifugation.
2. Soluble fraction –> precipitation / centrifugation.
3. Protein enriched fractions–> chromatography
4. Purified protein fractions

Question 2

Principles of isolation (first step) Difference in:

Answer 2

• Solubility
• Size
• Charge

Question 3

Proteins of milk: size and class

Answer 3

Caseins (80%) 50-300nm, more MW.
Whey proteins (20%) 3nm.

Question 4

Separation by size:

Answer 4

*Microfiltration: cream emulsion droplets > 0,1 microm
*Ultrafiltration: casein micelles
*Nanofiltration: whey proteins
*Reverse osmosis: lactose/salts
Solvent (remove exces water)

Question 5

Size fractionation of milk: steps

Answer 5

Whole milk: (MF) cream and skimmed milk, (UF) caseins and whey, whey fraction also fractionated with NF and many types of proteins concentrates ( purity 35-80 % proteins).

Question 6

An alternative to the size fractionation:

Answer 6

The separation based on solubiluty: using acid/rennet, precipitation of the caseins. Caseins precipitate at the pI or at the nutral pH of the milk that is 6.7, can precipitate after the rennet action, the enzyme action removes kappa casein.

Question 7

PRODUCTION OF CASEIN ISOLATES: isolation from milk by…. and product names….

Answer 7

1. Precipitation induced by:
   * Rennet- removal of k-casein : rennet casein
   * Acidification (to pH 4.6), readjustment to pH 6.8 with NaOH or KOH: acid casein (Na/K - caseinate).
2. Ultra- or microfiltration: micellar casein.

Question 8

When you separate the whey and caseins, there are not only one type of caseins or micells, There are many different molecules still present. TRUE OR FALSE.

Answer 8

TRUE: whey proteins(globular) beta lactoglobulin, alfa lactablumin, imminoglobulins, etc. Caseins (random coil) alfa s,1, alfa s,2 beta, kappa, etc.

Question 9

In soy 2 major proteins are present: glycinin and conglycinin. The SDS-PAGE shows the protein compostion of 2 protein isolates made from soy. Why is the protein composition different for each isolate?

Answer 9

In the steps of protein isolation, there are two majow steps that can change the protein composition. The extraction step where you solubilize certain proteins if you extract at a ceratin pH some molecules come into solutions others do not. Differences in pH during extraction or precipitation will result in differences in protein composition. Which proteins are present in the final isolate depends on the pH used and the solubility at the iso-electric point (pI) of the proteins.

Question 10

Solubility of the rennet casein? Isolationa and after isolation?

Answer 10

Solubility: precipitation takes places at any pH.
Isolation: is based on precipitation (neutral pH ) includes enzymatic treatment.
After isolation: pH remains neutral.