pH-dependent complexation of lysozyme with low methoxyl (LM) pectin

•Lysozyme can form electrostatic complexes with LM pectin.•Complex formation is dependent on both pH and lysozyme/LM pectin ratio.•The complexation phases were followed by intrinsic fluorescence changes.•Lysozyme conformation is modified during both the aggregation and dissociation phases.

In order to understand the effect of pH on the formation of electrostatic complexes between lysozyme and low methoxyl (LM) pectin, mixtures were prepared at a fixed lysozyme concentration (0.714 g.L−1) by progressive addition of LM pectin (from 0 to 4 g.L−1). Turbidity analysis allowed to determine specific conditions of pH and lysozyme/LM pectin ratio for optimal complex aggregation. The intrinsic fluorescence enhancement observed upon binding of LM pectin to lysozyme was correlated with the formation of intermolecular aggregates. Conversely, the intrinsic fluorescence decrease observed at higher LM pectin amounts was correlated with the dissociation of intermolecular aggregates. UV absorption spectroscopy showed modifications in lysozyme conformation during both the aggregation phase and the dissociation phase. The role of electrostatic interactions in the formation of lysozyme/LM pectin complexes is discussed in relation to the overall structure and the charge density profile of the two biopolymers.