Microwave processing of honey negatively affects honey antibacterial activity by inactivation of bee-derived glucose oxidase and defensin-1

Microwave (MW) thermal heating has been proposed as an efficient method for honey liquefaction, while maintaining honey quality criteria. However, little is known about the effects of MW thermal heating on honey antibacterial activity. In this study, we aimed to determine the effects of MW heating on the antibacterial activity of raw rapeseed honeys against Pseudomonas aeruginosa and Staphylococcus aureus, with a particular focus on two major bee-derived antibacterial components, defensin-1 and hydrogen peroxide (H₂O₂). Our results demonstrated that MW thermal heating completely abolished honey antibacterial activity whereas conventional thermal treatment at 45 and 55 °C did not affect the antibacterial activity of honey samples. A significant decrease in both glucose oxidase activity and H₂O₂ production as well as defensin-1 amount was observed in MW-treated samples. Given that defensin-1 and H₂O₂ are regular antibacterial components of all honeys, MW heating may have similar negative effects on every type of crystallized/liquid honey.