Preparation of and studies on the functional properties and bactericidal activity of the lysozyme-xanthan gum conjugate

•Lysozyme (Lyz) was conjugated to Xanthan Gum (XG) under controlled Maillard reaction.•The optimum reaction condition was pH 8.5 at 60 °C for 10 days.•The conjugate exhibits excellent solubility at different pHs and temperatures.•The heat stability, emulsion and foam stability and activity and antioxidant property improved significantly.•Conjugate has activity against G+ and G− bacteria and can be used as a natural preservative in foods.

The purpose of this research was to produce a xanthan gum-lysozyme conjugate (Lyz-XM) and to investigate the effect of conjugation on functional properties and antimicrobial properties of the conjugated products. The antimicrobial activity of Lyz is limited to Gram positive bacteria, but its antibacterial spectrum can be extended towards Gram negative bacteria by conjugation with carbohydrate through the Maillard reaction. Lyz was allowed to react with XG under mild Maillard reaction condition (pH 8.5 and 60 °C for 10 days) and conjugation was confirmed by SDS-PAGE, enzyme activity and determination of sugar content of the product. Results showed that under optimal conditions approximately 1.9 mmol XG was attached to one mol Lyz. The Lyz-XG conjugate showed higher solubility at acidic pHs and at different temperatures, increased heat stability with improved emulsion and foaming properties. Additionally, Lyz-XG conjugate showed antioxidant properties and significantly inhibited the growth of Staphylococcus aureus and Escherichia coli in a dose dependent manner. These findings may broaden food applications of Lyz as a functional ingredient with high quality emulsifier, foam producer or natural antibacterial agent in food or pharmaceutical industries.