Properties of lysozyme/sodium alginate complexes for the development of antimicrobial films

- Complexation of lysozyme by alginate occurs in two separate steps.
- Alginate concentration influences the size, electric charge and microstructure of complexes.
- The loss of the lysozyme enzymatic activity due to complexation is reversible.
- Lysozyme/alginate complexes can be used for making films with an antibacterial activity.

Complexation study of lysozyme (0.714 g/L) by sodium alginate at pH 7 showed that aggregates formation was a two-phase process. The first phase (from 0 to 0.1 g/L sodium alginate) corresponded to the combination of individual complexes to form aggregates which caused an increase of turbidity and average size and a rapid sedimentation. Charge neutralization estimated by ζ-potential measurements occurred at 0.1 g/L sodium alginate concentration. The second phase (from 0.1 to 4 g/L of sodium alginate) was characterized by the formation of aggregates having a less dense structure with higher average size despite the drop in turbidity and the high dispersion in the medium. Lysozyme enzymatic activity decreased upon complexation with sodium alginate but was fully recovered after calcium chloride addition. In order to check whether lysozyme reversible inactivation was only due to substrate diffusion limitation or to conformational changes upon complexation, fluorescence and UV-Vis absorption measurements were performed. Moreover, lysozyme/sodium alginate complexes were used to manufacture an edible antimicrobial film to target lysozyme sensitive microorganisms.

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