Silica Particles Functionalization with Thymol and Eugenol as a Novel Strategy to Control Histamine-Producing Bacteria

Histamine accumulation in foods poses significant public health risks, yet current control strategies present important limitations. This study assessed the in vitro antimicrobial activity of silica microparticles covalently functionalized with thymol (SiO2-THY) and eugenol (SiO2-EUG) against four representative histamine-producing bacterial strains: Raoultella planticola, Limosilactobacillus reuteri, Levilactobacillus hilgardii, and Pediococcus parvulus. For this purpose, functionalized particles were characterized by FESEM, zeta potential measurements, and elemental analysis, confirming successful immobilization of both compounds at comparable functionalization degrees (137–139 mg EOC/g SiO2). Functionalized materials exhibited significant antimicrobial activity against all tested strains, with reductions exceeding 3 logarithmic cycles at the lowest concentrations tested. This effect is attributed to the functionalized particles altering bacterial membrane fluidity and disrupting membrane potential, thereby impairing cellular homeostasis, as revealed by mechanistic assays. Among the strains confirmed as histamine producers, SiO2-THY and SiO2-EUG substantially reduced histamine formation, with reductions reaching up to approximately 100% at bactericidal concentrations and remaining significant at sub-inhibitory levels. These findings suggest that immobilized compounds interfere not only with bacterial growth but also with histamine biosynthetic pathways. Therefore, the use of silica-immobilized essential oil constituents represents a promising strategy for mitigating histamine accumulation and enhancing food safety. Nevertheless, further validation in relevant food matrices is required.