Introduction - Production of protein isolates

6 important questions on Introduction - Production of protein isolates

Which parts are separated by separation by size?

  • Cream
Microfiltration (MF)
  • Casein micelles
Ultrafiltration (UF)
  • Whey proteins
Nanofiltration (NF)
  • Lactose/salts
Reverse osmosis (RO)
  • Solvent

Which parts are separation by size fractionation of milk?

  • Whole milk --> cream
  • Skimmed milk --> caseins

  • Whey protein --> lactose
  • WPC-35
  • WPC-50
  • WPC-65
  • WPC-80
  • WPI-95

What happens in separation based on solubility? And how is it different for whey proteins and caseins?

Caused by addition of acid/rennet.

  • Whey proteins (globular)
    • Soluble at ~pH  4.6 (pI)
    • up to ~30 g/L
  • Caseins (random coil)
    • Precipitate
      • at ~pH 4.6
      • at natural pH after removal of k-casein (by rennet)

What are different kinds of casein isolates and how are they isolated?

  • Rennet casein --> precipitation induced by: rennet - removal of k-casein
  • Acid casein --> precipitation induced by acidification (to pH 4.6)
  • Na/K-caseinate --> precipitation induced by acidification (to pH 4.6) and readjustment to pH 6.8 (solubilise again) with NaOH or KOH
  • Micellar casein --> ultra- or microfiltration

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

  • 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 pI of the proteins

Differences in isolation methods of proteins result in:

Differences in: purity, composition and state of protein

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