Inactivation of Bacillus coagulans Spores by Pressure-assisted Thermal Processing

Abstract

Food sterilization has traditionally been associated with thermal processing at ≥121°C to ensure elimination of pathogenic spore-forming bacteria. Thermal processing alone tends to adversely affect the product’s freshness and quality attributes. Pressure-assisted thermal processing (PATP) offers new opportunities to overcome these limitations by treatment of foods at lower temperatures. This study was conducted to examine the lethality of PATP against the spores of Bacillus coagulans (an acid-tolerant spoilage bacterium) in a commercial tomato juice. The spores were suspended in deionized water, added to the samples (tomato juice at pH 4.2) at 108 CFU/ml, and treated at 600 MPa and temperatures of up to 105°C for various holding times (≤1.5 min). The viable numbers of spores were subsequently determined on tripticase soy and nutrient agars. A PATP treatment at 100°C for 2 min was found to be sufficient to inactivate the B. coagulans spores to an undetectable level (≤10 CFU/ml). The decimal reduction time (D-value) of the spores under these conditions was determined as 30 s. These findings demonstrate the efficacy of PATP treatment against heat and pressure-resistant bacterial spores; however, the level of inactivation will depend on the process conditions and composition of the suspending medium.