Impact of thermal treatment, pulsed electric fields, and high-pressure processing on the transcriptome of Escherichia coli ATCC 8739
Red fruits are valued for their vitamin C and polyphenol content, but traditional heat preservation methods used in juice and nectar production can significantly reduce these components. Therefore, alternative non-thermal methods are explored to inactivate foodborne pathogens like Escherichia coli while maintaining the nutritional value. However, knowledge about the effects of these technologies on bacterial cells is limited. This study analyzed differentially expressed genes of E. coli ATCC 8739 inoculated in strawberry nectar after exposure to three treatments with two sets of parameters each, namely thermal treatment, high-pressure processing (HPP), and moderate-intensity pulsed electric field (MIPEF). The highest inactivation efficiency was achieved with HPP at 400 MPa, 1 min, reducing microbial counts by 5.0±0.3 log cfu/mL, and thermal treatment at 60°C, 200 s, achieving a reduction of 4.4±0.2 log cfu/mL, while no inactivation was observed with MIPEF at 6 kV/cm. Transcriptomic analysis showed that thermal and HPP treatments caused similar molecular stress responses in E. coli. In both cases, the most overexpressed genes encoded outer membrane proteins, which may lead to the activation of the envelope stress response. Despite no microbial inactivation was revealed after MIPEF treatment, strong transcriptomic responses were observed, particularly in genes related to membrane integrity and metabolic activity. Numerous overexpressed genes associated with ABC transporters, outer membrane proteins, and lipoproteins were identified, which could increase the strain's virulence. This study provides insights into the stress response mechanisms induced by conventional and novel treatments. Nevertheless, further research is needed to investigate the long-term effects on bacterial populations. Overall design: RNA-seq profiling of E. coli ATCC 8739 inoculated in strawberry nectar after exposure to six different treatments, including thermal treatment, high pressure processing, and pulsed electric field (3 replicates)