Investigation of structural changes of β-casein and lysozyme at the gas-liquid interface during foam fractionation.
Purification and separation of proteins play a major role in biotechnology. Nowadays, alternatives to multistep operations suffering from low product yields and high costs are investigated closely amidst which one of the promising options is foam fractionation. The molecular behavior at the gas-liquid interface plays an important role in the formation and stabilization of enriched foam. This study for the first time correlates the physico-chemical parameters to the molecular structure in view of protein enrichment during foam fractionation of the two relatively different proteins lysozyme and β-casein employing biophysical techniques such as circular dichroism (CD) spectroscopy and infrared reflection absorption spectroscopy (IRRAS). In case of lysozyme, high enrichment was achieved at pH<pI in contrast to current opinion. This is due to partial unfolding and aggregation of the lysozyme molecules under favorable foaming conditions that resulted with high enrichment of foamed protein. Under these favorable conditions, CD spectra and IRRA spectra show that the unfolding of lysozyme is partially irreversible. However, the unfavorable foaming conditions, giving low enrichment, promote only minor structural changes and these changes are fully reversible. In case of β-casein, no pronounced unfolding can be observed using CD spectroscopy and IRRAS. The β-casein molecules adsorb and purely reorient at the gas-liquid interface, depending on favorable or unfavorable conditions.
Technical University Dortmund, Faculty of Biochemical and Chemical Engineering, Laboratory of Plant and Process Design, Emil-Figge-Str. 70, 44227 Dortmund, Germany.
Ivana
I
Barackov
Anika
A
Mause
Shobhna
S
Kapoor
Roland
R
Winter
Gerhard
G
Schembecker
Bernhard
B
Burghoff
D000042:Absorption; D000818:Animals; D002364:Caseins / Q000032:analysis / Q000737:chemistry*; D002417:Cattle; D005591:Chemical Fractionation / Q000379:methods*; D002645:Chickens; D002942:Circular Dichroism; D004867:Equipment Design; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D009113:Muramidase / Q000032:analysis / Q000737:chemistry*; D009994:Osmolar Concentration; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared; D013696:Temperature
D002364:Caseins; D009113:Muramidase