Enzymatic cross-linking of α-lactalbumin to produce nanoparticles with increased foam stability.
Hard colloidal nanoparticles (e.g. partly hydrophobised silica), are known to make foams with very high foam-stability. Nanoparticles can also be produced from proteins by enzymatic cross-linking. Such protein based particles are more suitable for food applications, but it is not known if they provide Pickering foam stabilisation to the same extent as hard colloidal particles. α-Lactalbumin (α-LA) was cross-linked with either microbial transglutaminase (mTG) or horseradish peroxidase (HRP) to produce α-LA/mTG and α-LA/HRP nanoparticles. With both enzymes a range of nanoparticles were produced with hydrodynamic radii ranging from 20-100 nm. The adsorption of nanoparticles to the air-water interface was probed by increase in surface pressure (Π) with time. In the beginning of the Π versus time curves, there was a lag time of 10-200 s, for nanoparticles with Rh of 30-100 nm, respectively. A faster increase of Π with time was observed by increasing the ionic strength (I = 0-125 mM). The foam-ability of the nanoparticles was also found to increase with increasing ionic strength. At a fixed I, the foam-ability of the nanoparticles decreased with increasing size while their foam-stability increased. Foams produced by low-shear whipping were found to be 2 to 6 times more stable for nanoparticles than for monomeric α-LA (Rh≈ 2 nm). At an ionic strength of 125 mM ionic strength and protein concentration ≥ 10 g L(-1), the foam-stability of α-LA/mTG nanoparticles (Rh = 100 nm, ρapp = 21.6 kg m(-3)) was 2-4 times higher than α-LA/HRP nanoparticles (Rh = 90 nm, ρapp = 10.6 kg m(-3)). This indicated that foam-stablity of nanoparticles is determined not only by size but also by differences in mesoscale structure. So, indeed enzymatic cross-linking of proteins to make nanoparticles is moving a step towards particle like behavior e.g. slower adsorption and higher foam stability. However, the cross-link density should be further increased to obtain hard particle-like rigidity and foam-stability.
Laboratory of Food Chemistry, Wageningen University, 6700 AA Wageningen, The Netherlands. peter.wierenga@wur.nl.
Surender K
SK
Dhayal
Roy J B M
RJ
Delahaije
Renko J
RJ
de Vries
Harry
H
Gruppen
Peter A
PA
Wierenga
D000327:Adsorption; D003432:Cross-Linking Reagents / Q000737:chemistry*; D006735:Horseradish Peroxidase / Q000737:chemistry; D007768:Lactalbumin / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry; D009994:Osmolar Concentration; D055550:Protein Stability; D011503:Transglutaminases / Q000737:chemistry; D014867:Water / Q000737:chemistry
D003432:Cross-Linking Reagents; D014867:Water; D007768:Lactalbumin; D006735:Horseradish Peroxidase; D011503:Transglutaminases