Pasteurization mechanism of S. aureus ATCC 25923 in walnut shells using radio frequency energy at lab level

Abstract

Radio frequency (RF) heating has been widely applied for pasteurizing food products. The pasteurization mechanism of pathogens using RF heating is still not clear. In this study, a 27.12 MHz RF system was used to process walnut shells (9%, w.b.) inoculated with S. aureus ATCC 25923. The changes on the gene level of S. aureus ATCC 25923 were evaluated by transcriptomics analysis. Results showed that treatment of S. aureus cells with RF heating resulted in the damage of cell integrity, as observed by scanning electron microscopy, sublethal damage detection, and extracellular adenosine triphosphate (ATP) detection analyses. A total of 449 differentially expressed genes was associated with nucleic-acid metabolism, translation, energy metabolism, cell membrane, and cell wall biosynthesis after RF treatment. Lipid metabolism-related genes (gcdH, ALDH, fadD, fadN, etc.) were all up-regulated, while cell wall synthesis related genes (SgtB, LysC, asd, tag, etc.) were down-regulated more than 2-fold after RF treatment. These results indicated that RF heating disrupted the cell membrane homeostasis and inhibited the synthesis of cell wall. In addition, the translational activity and energy metabolism were also altered after RF treatment. These results provide valuable insights into the pasteurization mechanism of S. aureus ATCC 25923 treated by RF heating.