Wang Xiaoyong, Li Yunqi, Wang Yu-Wen, Lal Jyotsana, Huang Qingrong
Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, New Jersey 08901, USA.
J Phys Chem B. 2007 Jan 25;111(3):515-20. doi: 10.1021/jp0632891.
Small-angle neutron scattering (SANS) has been used to investigate the microstructure of beta-lactoglobulin/pectin coacervates prepared by different initial protein/polysaccharide weight ratio (r), sodium chloride concentration (C(NaCl)), and pectin charge density. The higher r and higher pectin charge density lead to higher scattering intensity at small q range (0.007 Angstrom(-1) < q < 0.02 Angstrom(-1)), suggesting that the charges of pectin chains are screened significantly by the binding of oppositely charged protein molecules, leading to a tighter aggregation of pectin chains. On the other hand, the appearance of a shoulder peak at intermediate q range (0.04 Angstrom(-1) < q < 0.2 Angstrom(-1)) is used to interpret the formation of protein domains in beta-lactoglobulin/pectin coacervates. At C(NaCl) = 0.1 M, the coacervate of beta-lactoglobulin and pectin A does not show a shoulder peak at intermediate q range at r = 10:1, suggesting that protein molecules are separately bound on pectin chains. However, a shoulder peak appears at intermediate q range at r = 20:1 and 30:1, and the average protein domain size estimated from the shoulder peak position is 7.2 and 8.5 nm, respectively, for these two coacervates. When C(NaCl) increases from 0.05 to 0.2 M, the shoulder peak shifts toward smaller q and becomes broader, indicating that the addition of a higher amount of salt leads to a more heterogeneous coacervate structure. Pectin B with a lower linear charge density favors the formation of larger protein domains. The formation of protein domains in beta-lactoglobulin/pectin coacervates is partially ascribed to the self-aggregation of beta-lactoglobulin molecules. Two kinds of microstructures of beta-lactoglobulin/pectin coacervates with and without observable protein domains have been proposed.
小角中子散射（SANS）已被用于研究通过不同的初始蛋白质/多糖重量比（r）、氯化钠浓度（C(NaCl)）和果胶电荷密度制备的β-乳球蛋白/果胶凝聚层的微观结构。较高的r和较高的果胶电荷密度导致在小q范围（0.007 Å⁻¹ < q < 0.02 Å⁻¹）有更高的散射强度，这表明果胶链的电荷通过带相反电荷的蛋白质分子的结合而被显著屏蔽，导致果胶链更紧密地聚集。另一方面，在中间q范围（0.04 Å⁻¹ < q < 0.2 Å⁻¹）出现的肩峰用于解释β-乳球蛋白/果胶凝聚层中蛋白质结构域的形成。在C(NaCl) = 0.1 M时，β-乳球蛋白和果胶A的凝聚层在r = 10:1时在中间q范围未显示肩峰，这表明蛋白质分子分别结合在果胶链上。然而，在r = 20:1和30:1时在中间q范围出现了肩峰，对于这两种凝聚层，从肩峰位置估计的平均蛋白质结构域大小分别为7.2和8.5 nm。当C(NaCl)从0.05 M增加到0.2 M时，肩峰向较小的q移动并变宽，表明添加更多的盐会导致凝聚层结构更不均匀。线性电荷密度较低的果胶B有利于形成更大的蛋白质结构域。β-乳球蛋白/果胶凝聚层中蛋白质结构域的形成部分归因于β-乳球蛋白分子的自聚集。已经提出了β-乳球蛋白/果胶凝聚层具有和不具有可观察到的蛋白质结构域的两种微观结构。
