Effect of Structural Features of Pectin on Its Complexation with Lysozyme
Interaction of lysozyme (Lys) with pectins differing in total or local charges (blockwise and statistical distribution of the methoxylated groups, BP and SP), and also different degree of methoxylation (DM) was studied by use of dynamic light scattering, turbidimetry, brightfield imaging, and electrophoretic mobility. SP 16.2, 38.2, and BP 16.9, 33.1 form at pH 5.1, ionic strength <i>I</i> = 0.01, and <i>q</i> < <i>q</i><sub>mах</sub> water soluble complexes in the concentration range of mixtures from <i>q</i> ≅ 7 × 10<sup>–4</sup> до <i>q</i> = 3.0 × 10<sup>–3</sup>, where <i>q</i>-pectin/Lys weight ratio, and water insoluble complexes at <i>q</i> > 3 × 10<sup>–3</sup>. For SP 66.5 and BP 68.2 these values were higher (from <i>q</i> ≅ 3 × × 10<sup>–3</sup> to <i>q</i> ≅ 0.01, and <i>q</i> > 0.01). Complexes of Lys with BP has large sizes (15–20 µm) for all DM, whereas the average sizes of complexes Lys/SP are much less (from 0.6 µm to 3 µm) and they depened on DM. Complexes of Lys with BP has gel-like morphology for all DM, whereas complexes with SP were liquid coacervate or gel like depending on on DM. Critical values of the ionic strength <i>I</i><sub>set</sub>, above that complexes did not formed was 0.11. At that, <i>I</i><sub>set</sub> and pH<sub>set</sub> values for BP/Lys systems were not depended on DM of pectin. For SP/Lys systems these values decreases when DM increase. Effect of <i>I</i> on complexation has a nonmonotonic character displaying a maximum in complex formation at <i>I</i> = 0.03–0.06. Understanding of effect of the total and local charges of pectin on its complexation with protein is important for prediction of the structural stability of food products.