Abstract
In this study, novel spore pouches were developed using mashed potato as a food model inoculated with either Geobacillus stearothermophilus or Clostridium sporogenes 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 (*L-values). Inactivation equivalent to of 1–2 Log CFU/g and >6 Log CFU/g for Geobacillus stearothermophilus and Clostridium sporogenes 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 G. stearothermophilus and C. sporogenes 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 C. sporogenes 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.
Highlights
Any novel sterilization technology brings along the necessity to develop methods to ensure that the coldest regions inside the food would receive enough treatment to achieve the inactivation of microorganisms to ensure food safety
To address this research gap, the current study investigated the use of spore pouches that were developed using food model inoculated with bacterial spores packed in microwavable Cryovac BNB1 pouch (15 mm2 ) (Cryovac, Hamilton, New Zealand)
Bacterial spore pouches were developed as a method to evaluate thermal exposure on specific locations inside food trays
Summary
Any novel sterilization technology brings along the necessity to develop methods to ensure that the coldest regions inside the food would receive enough treatment to achieve the inactivation of microorganisms (mesophiles and thermophiles) to ensure food safety. Induced microwave pasteurization and sterilization (CiMPAS) is an emerging thermal technology that combines hot water immersion and microwave energy (915 MHz) to achieve sterilization in a shorter time as compared to the conventional technologies [1,2]. Microwave sterilization uses less processing time as compared to conventional retorting and thereby the exposure of the nutrients in food to high temperatures is reduced to allow better nutrient retention [1,2,4]. A challenge with microwave sterilization is the non-uniform heating that could lead to the formation of cold spots in the processed products [5,6]. The presence of cold spots or regions that have been less thermally processed might result in incomplete bacterial inactivation. Hot or cold spots may lead to uneven cooking, consequent undesirable sensory properties and nutrient losses
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