Synergistic antibacterial effects of zinc oxide with cinnamaldehyde or carvacrol against Brochothrix thermosphacta and their application in chicken breast preservation

Brochothrix thermosphacta (B. thermosphacta) is a significant spoilage organism in meat products, posing a major challenge to food safety. The research investigated the individual and combined antibacterial effects of zinc oxide nanoparticles (ZnO), cinnamaldehyde (Cin) and carvacrol (Car) against B. thermosphacta. The findings showed that ZnO, Cin and Car had considerable antibacterial activity, with minimum inhibitory concentrations of 4, 0.5 and 2 mg/mL respectively. Combination of ZnO-Cin and ZnO-Car assays demonstrated synergistic interactions, and the fractional inhibitory concentration index was 0.375 and 0.5, respectively. Scanning electron microscopy, extracellular conductivity, nucleic acid leakage, and intracellular enzyme activity demonstrated that these treatments exerted antibacterial effects by disrupting cell wall/membrane integrity, permeabilizing membranes, and leaking cell contents. Furthermore, ZnO and Cin treatments caused substantial accumulation of intracellular reactive oxygen species, while Car primarily exerted its effects through the disruption of membrane structure. Metabolomic profiling revealed that the ZnO-Cin synergy primarily disrupted the synthesis of aromatic amino acids and cofactors, while the ZnO-Car synergy primarily affected nucleotide metabolism, the TCA cycle, and energy transduction. The combination of these treatments, along with their synergistic effects, resulted in an even greater disruption of the microbial metabolic system. The storage experiment further corroborated that both ZnO-Cin and ZnO-Car combinations exert a pronounced inhibitory effect against B. thermosphacta mediated spoilage in fresh chicken meat. This study provided a theoretical foundation for the development of effective natural composite antimicrobials against B. thermosphacta.