Abstract

The interaction between lysozyme (Lys) and pectins with different net and local charges and with block (BD) and random (RD) distributions of methoxyl groups is studied via dynamic light scattering, turbidimetry, high-resolution optical microscopy, and electrophoretic mobility measurements. RD 16.2, RD 38.2, BD 16.9, and BD 33.1 form water-soluble complexes at pH 5.1, ionic strength I = 0.01, and q < q_mах, within the range of mixture compositions q spanning ≅ 7 × 10^–4 to 3.0 × 10^–3, where q is the weight ratio between pectin and Lys; while water-insoluble complexes are formed for q > 3 × 10^–3. The corresponding parameters for RD 66.5 and BD 68.2 are higher: q ≅ 3 × 10^–3 up to q ≅ 0.01, and q higher than 0.01. Optical microscopy shows that the complexes between Lys and BDs are large (15–20 μm) for all studied values of the degree of methoxylation (DM), while the average size of RD-based complexes is substantially lower (from 0.6 to 3 μm) and depends on the DM. The BD-based complexes have a gel-like morphology irrespective of the DM, whereas particles of RD-based complex have the form of both coacervate drops and gel-like particles, depending on the DM. The threshold value for ionic strength I_set above which Lys does not form complexes with RD and BD is found to be 0.11. That being so, the values for I_set and pH_set for the BD/Lys systems are independent of the pectin DM, while for the RD/Lys systems these parameters diminish considerably with an increase in the DM. The dependence of complexation of Lys and pectin on I has a non-monotonic character with a maximum at I = 0.03 and 0.06 for RD and BD, respectively. Our understanding of the effect that the total charge of a pectin molecule and its distribution along the chain has on the complexation of pectin and a protein is important for our ability to predict the stability of the food product structure.

中文翻译：

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果胶的结构特征对其与溶菌酶复合的影响

摘要

通过动态光散射，比浊法，高分辨率光学显微镜和电泳迁移率测量研究了溶菌酶（Lys）和果胶之间具有不同净电荷和局部电荷以及甲氧基的嵌段（BD）和随机（RD）分布的相互作用。在pH 5.1 RD 16.2，RD 38.2，BD 16.9，和33.1 BD形式水溶性络合物，离子强度我= 0.01，和q < q _mах，混合物的组合物的范围内的q跨越≅7×10 ^-4〜3.0× 10 ^–3，其中q是果胶与Lys的重量比；当q > 3×10 ^–3时形成水不溶性配合物。为RD 66.5和68.2 BD对应的参数是更高：q ≅3×10 ^-3到q ≅0.01，和q高于0.01。光学显微镜显示，对于所有研究的甲氧基化度（DM）值，Lys和BDs之间的复合物都很大（15– 20μm），而基于RD的复合物的平均尺寸则要低得多（从0.6到3μm）并取决于DM。取决于DM，基于BD的复合物具有凝胶状形态，而取决于DM，基于RD的复合物的颗粒具有凝聚液滴和凝胶状颗粒的形式。对离子强度的阈值予_组高于该值，Lys不会与RD和BD形成络合物，发现其为0.11。因此，BD / Lys系统的I _set和pH _set值独立于果胶DM，而RD / Lys系统的这些参数随着DM的增加而显着降低。Lys和果胶复合物对I的依赖性具有非单调性，RD和BD的最大值分别为I = 0.03和0.06。我们对果胶分子的总电荷及其沿链分布的影响对果胶和蛋白质复合的影响的理解，对于我们预测食品结构稳定性的能力非常重要。