Schmitt Christophe, da Silva Tânia Palma, Bovay Claudine, Rami-Shojaei Sabrina, Frossard Philippe, Kolodziejczyk Eric, Leser Martin E
Department of Food Science, Nestlé Research Center, Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland.
Langmuir. 2005 Aug 16;21(17):7786-95. doi: 10.1021/la0510984.
The electrostatic complexation between beta-lactoglobulin and acacia gum was investigated at pH 4.2 and 25 degrees C. The binding isotherm revealed a spontaneous exothermic reaction, leading to a DeltaHobs = -2108 kJ mol(-1) and a saturation protein to polysaccharide weight mixing ratio of 2:1. Soluble electrostatic complexes formed in these conditions were characterized by a hydrodynamic diameter of 119 +/- 0.6 nm and a polydispersity index of 0.097. The effect of time on the interfacial and foaming properties of these soluble complexes was investigated at a concentration of 0.1 wt % at two different times after mixing (4 min, referred as t approximately 0 h and t = 24 h). At t approximately 0 h, the mixture is mainly made of aggregating soluble electrostatic complexes, whereas after 24 h these complexes have already insolubilize to form liquid coacervates. The surface elasticity, viscosity and phase angle obtained at low frequency (0.01 Hz) using oscillating bubble tensiometry revealed higher fluidity and less rigidity in the film formed at t approximately 0 h. This observation was confirmed by diminishing bubble experiments coupled with microscopy of the thin film. It was thicker, more homogeneous and contained more water at t approximately 0 h as compared to t = 24 h (thinner film, less water). This led to very different gas permeability's of Kt approximately 0 h = 0.021 cm s(-1) and Kt=24 h) = 0.449 cm s(-1), respectively. Aqueous foams produced with the beta-lactoglobulin/acacia gum electrostatic complexes or coacervates exhibited very different stability. The former (t approximately 0 h) had a stable volume, combining low drainage rate and mainly air bubble disproportionation as the destabilization mechanism. By contrast, using coacervates aged for 24 h, the foam was significantly less stable, combining fast liquid drainage and air bubble destabilization though fast gas diffusion followed by film rupture and bubble coalescence. The strong effect of time on the air/water interfacial properties of the beta-lactoglobulin/acacia gum electrostatic complexes can be understood by their reorganization at the interface to form a coacervate phase that is more fluid/viscous at t approximately 0 h vs rigid/elastic at t = 24 h.
在pH 4.2和25℃条件下研究了β-乳球蛋白与阿拉伯胶之间的静电络合作用。结合等温线显示这是一个自发的放热反应,导致ΔHobs = -2108 kJ mol⁻¹,蛋白质与多糖的饱和重量混合比为2:1。在这些条件下形成的可溶性静电络合物的特征在于流体动力学直径为119±0.6 nm,多分散指数为0.097。在混合后的两个不同时间(4分钟,记为t≈0 h和t = 24 h),以0.1 wt%的浓度研究了时间对这些可溶性络合物的界面和发泡性能的影响。在t≈0 h时,混合物主要由聚集的可溶性静电络合物组成,而在24 h后这些络合物已经不溶解形成液体凝聚层。使用振荡气泡张力测定法在低频(0.01 Hz)下获得的表面弹性、粘度和相角表明,在t≈0 h时形成的膜具有更高的流动性和更低的刚性。通过减少气泡实验并结合薄膜显微镜观察证实了这一观察结果。与t = 24 h(薄膜、水少)相比,在t≈0 h时它更厚、更均匀且含水量更高。这导致气体渗透率非常不同,Kt≈0 h = 0.021 cm s⁻¹和Kt = 24 h = 0.449 cm s⁻¹。用β-乳球蛋白/阿拉伯胶静电络合物或凝聚层产生的水性泡沫表现出非常不同的稳定性。前者(t≈0 h)具有稳定的体积,结合了低排水率,并且主要以气泡歧化为失稳机制。相比之下,使用老化24 h的凝聚层时,泡沫的稳定性明显较差,结合了快速的液体排水和气泡失稳,即通过快速的气体扩散,随后是膜破裂和气泡聚并。时间对β-乳球蛋白/阿拉伯胶静电络合物的气/水界面性质的强烈影响可以通过它们在界面处的重组来理解,即在t≈0 h时形成更流体/粘性的凝聚层相,而在t = 24 h时形成刚性/弹性的凝聚层相。