Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 degrees C), high pressure processing (HPP; 700 MPa, 35 degrees C), and thermal processing (TP; 105 degrees C, 0.1 MPa) was investigated. Bacillus amyloliquefaciens spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 x 10(8) CFU/mL. B. amyloliquefaciens spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 degrees C. In conclusion, addition of some organic acids provided significant lethality enhancement (P < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.