Monitoring Sublethal Injury in During Heat Treatment of Pork Frankfurter-Type Sausages: A Single-Cell vs. Population Level Approach.

is a foodborne pathogen capable of contaminating ready-to-eat meat products, e.g., frankfurters. Post-packaging mild heat treatment via water immersion is commonly employed; however, this may be sublethal to cells located in protected niches or beneath the product surface. The objectives of this study were to evaluate thermal injury of on frankfurters at single-cell versus population level and to comparatively estimate pathogens' physiological status. Pork frankfurter-type sausages were inoculated (. 7.0-7.5 log CFU/cm) with strain EGDE-e. Heat treatment was performed at 61 °C (. 60 min) and 64 °C (. 12 min). To determine the injured subpopulation from the total, tryptic soy agar with 0.6% yeast extract (TSAYE), supplemented or not with 5% NaCl, was used. Plating-based quantification of injured cells was compared to CFDA/PIstained cells analysed by fluorescence microscopy and quantified with Fiji software. Injury was recorded mainly after 2 and 4 min at 64 °C, whereas no injury was detected at 61 °C, at population level. Following exposure to 61 °C for 60 min, culturable cells dropped below the enumeration limit (0.3 log CFU/cm), while a considerable number of CFDA/PI and CFDA/PI cells indicated viable-but-non-culturable induction and sublethal injury, respectively. These findings suggest that non-culturability may limit the accuracy of solely culture-based enumeration methods.