The inactivation of Bacillus subtilis spores using a combination of potassium sorbate and thermal treatments and exploring the underlying mechanisms

Abstract This study evaluated potassium sorbate (1 and 2 g/L) combined with heat (80, 90, and 100°C for 30, 60 and 90 min) for inactivating Bacillus subtilis spores. Plate counts, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) assessed lethality and structural responses. The combination yielded synergistic inactivation; the strongest effect (2.12 log CFU/mL reduction) occurred at 2 g/L sorbate and 90°C for 60 min. Flow cytometry showed a rightward shift of FL2 histograms and higher propidium-iodide fluorescence, evidencing increased inner-membrane permeability. FTIR indicated perturbation of membrane lipids, peptidoglycan disruption, and denaturation of nucleic acids and proteins, aligning with SEM-observed surface damage. Collectively, sorbate plus moderate heat compromises multiple protective barriers of spores and enhances killing, offering mechanistic insight and a practical route to lower-intensity sterilization in food processing.