Strong and Consistently Synergistic Inactivation of Spores of Spoilage-AssociatedBacillusandGeobacillusspp. by High Pressure and Heat Compared with Inactivation by Heat Alone

Abstract

ABSTRACTThe inactivation of spores of four low-acid food spoilage organisms by high pressure thermal (HPT) and thermal-only processing was compared on the basis of equivalent thermal lethality calculated at a reference temperature of 121.1°C (Fz121.1°C, 0.1 MPa or 600 MPa) and characterized as synergistic, not different or protective. In addition, the relative resistances of spores of the different spoilage microorganisms to HPT processing were compared. Processing was performed and inactivation was compared in both laboratory and pilot scale systems and in model (diluted) and actual food products. Where statistical comparisons could be made, at least 4 times and up to around 190 times more inactivation (log10reduction/minute atFTz121.1°C) of spores ofBacillus amyloliquefaciens,Bacillus sporothermodurans, andGeobacillus stearothermophiluswas achieved using HPT, indicating a strong synergistic effect of high pressure and heat.Bacillus coagulansspores were also synergistically inactivated in diluted and undiluted Bolognese sauce but were protected by pressure against thermal inactivation in undiluted cream sauce. Irrespective of the response characterization,B. coagulansandB. sporothermoduranswere identified as the most HPT-resistant isolates in the pilot scale and laboratory scale studies, respectively, andG. stearothermophilusas the least in both studies and all products. This is the first study to comprehensively quantitatively characterize the responses of a range of spores of spoilage microorganisms as synergistic (or otherwise) using an integrated thermal-lethality approach (FTz). The use of theFTzapproach is ultimately important for the translation of commercial minimum microbiologically safe and stable thermal processes to HPT processes.