Lethality enhancement of pressure-assisted thermal processing against Bacillus amyloliquefaciens spores in low-acid media using antimicrobial compounds

Pressure-assisted thermal processing (PATP; 500-700 MPa, 90-121 °C) offers new opportunities to sterilize low-acid foods while preserving quality attributes to an extent greater than is possible with traditional thermal processing (TP). This study was conducted to evaluate the possibility of enhancing PATP lethality against the spores of Bacillus amyloliquefaciens, by sensitizing the spores with selected antimicrobial compounds (including emphasis on the use of natural antimicrobials) prior to treatment. A spore crop of B. amyloliquefaciens TMW 2.479 Fad 82, that had previously shown high resistance to combined pressure-heat treatment, was prepared on Nutrient Agar medium supplemented with 10 mg L−1 MnSO4·H2O and incubated at 32 °C for 3 d. Spores were inoculated (at ∼107-108 CFU mL−1 inoculum level) in HEPES buffer (pH ≤ 7.0) or selected low-acid foods (pH 5.2-5.6) with or without added antimicrobial compounds. The samples were then treated at 600 MPa and 105 °C (PATP) or 0.1 MPa and 105 °C (TP) for various holding times. Among different compounds tested, low-molecular-weight chitosan, and combination of chitosan with some surfactants were most effective (P < 0.05) in enhancing the PATP and TP lethality. This study suggests that certain antimicrobials can be added to the low-acid media prior to PATP or TP treatment to enhance the efficacy of the process. The treatment allows sterilization of low-acid foods at lower process temperatures thus ensuring better preservation of quality attributes.