Dhayal Surender K, Delahaije Roy J B M, de Vries Renko J, Gruppen Harry, Wierenga Peter A
Laboratory of Food Chemistry, Wageningen University, 6700 AA Wageningen, The Netherlands.
Soft Matter. 2015 Oct 28;11(40):7888-98. doi: 10.1039/c5sm01112d. Epub 2015 Sep 1.
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.
已知硬质胶体纳米颗粒（如部分疏水化的二氧化硅）能产生具有极高泡沫稳定性的泡沫。纳米颗粒也可通过酶促交联由蛋白质制备。这种基于蛋白质的颗粒更适合食品应用，但尚不清楚它们是否能像硬质胶体颗粒一样提供同等程度的皮克林泡沫稳定作用。α-乳白蛋白（α-LA）与微生物转谷氨酰胺酶（mTG）或辣根过氧化物酶（HRP）交联，以制备α-LA/mTG和α-LA/HRP纳米颗粒。使用这两种酶都制备出了一系列流体动力学半径在20 - 100 nm范围内的纳米颗粒。通过表面压力（Π）随时间的增加来探究纳米颗粒在空气-水界面的吸附情况。在Π对时间的曲线起始阶段，对于流体力学半径分别为30 - 100 nm的纳米颗粒，存在10 - 200 s的滞后时间。通过增加离子强度（I = 0 - 125 mM）观察到Π随时间的增加更快。还发现纳米颗粒的发泡能力随离子强度的增加而增强。在固定的离子强度下，纳米颗粒的发泡能力随尺寸增大而降低，而其泡沫稳定性则增强。发现通过低剪切搅拌产生的泡沫，纳米颗粒的稳定性比单体α-LA（流体力学半径≈2 nm）高2至6倍。在离子强度为125 mM且蛋白质浓度≥10 g L⁻¹时，α-LA/mTG纳米颗粒（流体力学半径 = 100 nm，表观密度 = 21.6 kg m⁻³）的泡沫稳定性比α-LA/HRP纳米颗粒（流体力学半径 = 90 nm，表观密度 = 10.6 kg m⁻³）高2 - 4倍。这表明纳米颗粒的泡沫稳定性不仅由尺寸决定，还由中尺度结构的差异决定。所以，实际上通过酶促交联蛋白质制备纳米颗粒正朝着类似颗粒的行为迈进，例如吸附较慢和泡沫稳定性更高。然而，交联密度应进一步提高以获得类似硬质颗粒的刚性和泡沫稳定性。
