Development of Bacterial Spore Pouches as a Tool to Evaluate the Sterilization Efficiency—A Case Study with Microwave Sterilization Using <i>Clostridium sporogenes</i> and <i>Geobacillus stearothermophilus</i>

• Main Authors: Aswathi Soni, Jeremy Smith, Richard Archer, Amanda Gardner, Kris Tong, Gale Brightwell
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Foods
• Subjects: microwave; sterilization; <i>Geobacillus</i>; <i>Clostridium</i>; spores; inactivation
• Online Access: https://www.mdpi.com/2304-8158/9/10/1342

In this study, novel spore pouches were developed using mashed potato as a food model inoculated with either <i>Geobacillus stearothermophilus</i> or <i>Clostridium sporogenes</i> spores. These spore pouches were used to evaluate the sterilization efficiency of Coaxially induced microwave pasteurization and sterilization (CiMPAS) as a case study. CiMPAS technology combines microwave energy (915 MHz) along with hot water immersion to sterilize food in polymeric packages. The spore pouches were placed at pre-determined specific locations, especially cold spots in each food tray before being processed using two regimes (R-121 and R-65), which consisted of 121 °C and 65 °C at 12 and 22 kW, respectively, followed by recovery and enumeration of the surviving spores. To identify cold spots or the location for inoculation, mashed potato was spiked with Maillard precursors and processed through CiMPAS, followed by measurement of lightness values (*<i>L</i>-values). Inactivation equivalent to of 1–2 Log CFU/g and >6 Log CFU/g for <i>Geobacillus stearothermophilus</i> and <i>Clostridium sporogenes</i> spores, respectively was obtained on the cold spots using R-121, which comprised of a total processing time of 64.2 min. Whereas, inactivation of <1 and 2–3 Log CFU/g for <i>G. stearothermophilus</i> and <i>C. sporogenes</i> spores, respectively on the cold spots was obtained using R-65 (total processing time of 68.3 min), whereas inactivation of 1–3 Log CFU/g of <i>C. sporogenes</i> spores was obtained on the sides of the tray. The results were reproducible across three processing replicates for each regime and inactivation at the specific locations were clearly distinguishable. The study indicated a strong potential to use spore pouches as a tool for validation studies of microwave-induced sterilization.