Physicochemical properties of modified antimicrobials and the effects on efficacy against foodborne pathogens

The objective of this study was to examine the relationship between physicochemical properties and antimicrobial activity of certain chemical compounds. Antimicrobial activity against Listeria monocytogenes and adsorption kinetics data were examined to determine if a correlation exists. For potassium sorbate, a commonly used antimicrobial, a relationship appears to exist between the pseudo-critical micellar concentration and the minimum inhibitory concentration. Lysozyme, a naturally occurring antimicrobial, was treated with ultrasound at various power levels and treatment times to examine the effects of sonication on both physicochemical properties and antimicrobial activity.

Ultrasound-treated lysozyme was found to give different adsorption kinetic data than native lysozyme, and variation between treatments was observed. Initially it was believed that three states of lysozyme were observed, native, partially denatured, and fully denatured. The partially denatured lysozyme had increased antimicrobial activity against L. monocytogenes, and the fully denatured lysozyme retained some of its antimicrobial activity. This contrasted previous work that reported that fully denatured lysozyme lost antimicrobial and enzymatic activity.

Thermal analysis using differential scanning calorimetry was performed on native and ultrasound-treated lysozyme. Analysis showed that lysozyme that gave adsorption kinetic data indicating full denaturation was not actually completely unfolded. Thermal analysis of heat-treated lysozyme showed full denaturation, as did adsorption kinetics studies. It was concluded that ultrasound treatment of lysozyme resulted in different states of partial denaturation, rather than partial and full denaturation.