Kinetics of Bacillus cereus Spore Inactivation in Cooked Rice by Combined Pressure–Heat Treatment

Abstract

The efficacy of pressure-heat treatment was evaluated for the inactivation of Bacillus cereus spores in cooked rice. The spores of B. cereus ATCC 9818 were inoculated (1.1 × 10(8) CFU/g) in a parboiled rice product (pH 6.0, water activity of 0.95) and inactivated to an undetectable level (<10 CFU/g) by treatment of 600 MPa and process temperatures of 60 to 85 °C or 0.1 MPa and 85 °C. Kinetic inactivation parameters were estimated with linear and nonlinear models. The potential recovery of injured bacteria was also evaluated during storage of the treated product for 4 weeks at 4 and 25 °C. Depending on the process temperature, a 600-MPa treatment inactivated spores by 2.2 to 3.4 log during the 30-s pressure come-up time, and to below the detection limit after 4- to 8-min pressure-holding times. In contrast, a 180-min treatment time was required to inactivate the spores to an undetectable level at 0.1 MPa and 85 °C. The decimal reduction time of spores inactivated by combined pressure-heat treatment ranged from 1.08 to 2.36 min, while it was 34.6 min at 85 °C under atmospheric conditions. The nonlinear Weibull model scale factor increased, and was inversely related to the decimal reduction time, and the shape factor decreased with increasing pressure or temperature. The recovery of injured spores was influenced by the extent of pressure-holding time and process temperature. This study suggests that combined pressure-heat treatment could be used as a viable alternative to inactivate B. cereus spores in cooked rice and extend the shelf life of the product.

High pressure processing of milk: Modeling the inactivation of psychrotrophic Bacillus cereus spores at 38–70 °C

“…For example, increasing the temperature from 38 to 70°C at 600 MPa for 40 min increased the B. cereus spore inactivation in reconstituted milk by 3.5 log. Similar observations were reported with spores of B. cereus LMG 6910 (=ATCC 7004) and ATCC 9818, Alicyclobacillus acidoterrestris and Clostridium botulinum with 600 MPa HPP in combination with heat (van Opstal et al, 2004;Margosch et al, 2006;Silva et al, 2012;Vercammen et al, 2012;Daryaei et al, 2013).…”

“…For the two strains modeled, the b value increased from 0.08-0.10 to 0.55-0.67 as the temperature increased from 38°C to 70°C. Daryaei et al (2013) also obtained an increase of b from 0.81 to 1.66 as the 600 MPa HPP temperature was increased from 60 to 85°C. The log b was found to be linearly dependent on the pressure-thermal process temperature (0.97 6 R 2 6 0.99) and pressure (R 2 = 0.95) (Fig.…”

“…The estimated specific energy to deliver 5 log spore reduction for a HPP-70°C-40 min process was 439 kJ/L and for the equivalent 90°C-10 min thermal process was 348 kJ/L, suggesting a higher energy demand for the pressure-thermal method. Lower temperatures for the pressure-thermal process were also documented by Daryaei et al (2013) and Luu-Thi et al (2014) for mesophilic B. cereus spores. Daryaei et al (2013) reported 4.0 log reductions for ATCC 9818 in cooked rice after 600 MPa-85°C-4 min, as opposed to <0.4 log reductions for a thermal process at the same conditions (85°C-4 min).…”

“…nisin and sucrose laurate) or an additional control hurdle (e.g. olive powder) to inactivate B. cereus spores has been investigated (Fornari et al, 1995;Gola et al, 1996;Arroyo et al, 1997;Raso et al, 1998;Rovere et al, 1998;Meyer et al, 2000;Shearer et al, 2000;McClements et al, 2001;Lopez-Pedemonte et al, 2003;van Opstal et al, 2004;Aoyama et al, 2005;Scurrah et al, 2006;Shigeta et al, 2007;Ju et al, 2008;Robertson et al, 2008;Marco et al, 2011;Daryaei et al, 2013). B. cereus spore log reductions between 1 and P7 were achieved, depending on the conditions applied and the spore resistance.…”

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

“…It is desirable to reduce further the thermal effect (to 105 C, under pressure) before PATP becomes a commercially relevant option for preserving low-acid foods. An intermediate pathway for commercialization of pressureheat-processed products has been processing low-acid foods by milder pressure-heat (60e90 C under pressure) and distributing them under refrigeration (Daryaei, Balasubramaniam, & Legan, 2013;Van Opstal, Bagamboula, Vanmuysen, Wuytack, & Michiels, 2004).…”