Effects of superheated steam on Geobacillus stearothermophilus spore viability

AIMS: To examine the effect of processing with superheated steam (SS) on Geobacillus stearothermophilus ATCC 10149 spores. METHODS AND RESULTS: Two inoculum levels of spores of G. stearothermophilus were mixed with sterile sand and exposed to SS at 105-175 degrees C. The decimal reduction time (D-value) and the thermal resistance constant (z-value) were calculated. The effect of cooling of spores between periods of exposure to SS was also examined. A mean z-value of 25.4 degrees C was calculated for both inoculum levels for SS processing temperatures between 130 degrees C and 175 degrees C. CONCLUSIONS: Spore response to SS treatment depends on inoculum size. SS treatment may be effective for reduction in viability of thermally resistant bacterial spores provided treatments are separated by intermittent cooling periods. SIGNIFICANCE AND IMPACT OF THE STUDY: There is a need for technologies that require short thermal processing times to eliminate bacterial spores in foods. The SS processing technique has the potential to reduce microbial load and to modify food texture with less energy in comparison to commonly used hot air treatment. This work provides information on the effect of SS processing parameters on the viability of G. stearothermophilus spores.