Protection of lactoperoxidase activity with sugars during lyophilization and evaluation of its antibacterial properties

The purpose of the present study was to compare the stabilizing effect of four disaccharides alone or in combination on the lactoperoxidase (LP) derived from bovine milk during lyophilization. Sucrose, lactose, maltose, and trehalose at different concentrations (5-500 mM) were used to compare their protective effects on LP activity. The activity of lyophilized and native LP enzyme was evaluated using the procedure of Schindler with slight modifications. The antibacterial activity of the lyophilized enzyme against Pseudomonas aeroginosa, Escherichia coli, and Staphylococcus aureus was also investigated using the antimicrobial effectiveness test. Trehalose at concentration of 500 mM was the most effective cryoprotectant in protecting the enzyme activity. It preserved LP activity for 40 days, while the native enzyme lost its activity after 6 days. Combinations of disaccharides resulted in an increment in the stability of the enzyme, compared to the native enzyme. Combination of 200 mM trehalose and 200 mM sucrose were found most effective cryoprotectant in freeze-drying of LP. The lyophilized LP decreased the growth rate of Ps.aeroginosa, E.coli, and S.aureus between up to 30.8% in 10(6) cfu/ml and 53.3% in 10(5) cfu/ml. Antimicrobial efficacy of LP was more pronounced when 10(5) cfu/ml was used as compared to 10(6) cfu/ml.