Effect of mild steaming treatment on the inactivation of Salmonella, Listeria monocytogenes, Escherichia coli O157:H7 and their surrogates on black peppercorns

Abstract

The microbial safety of black peppercorns (Piper nigrum L.) has raised concerns due to increasing numbers of reported foodborne outbreaks and food safety alerts. To avoid quality degradation caused by excessive thermal processing, mild steaming treatments (<80 °C) were tested in the present study as a promising solution to inactivate bacterial pathogens while maintaining the product quality of black peppercorns. Whole black peppercorns at three different water activities (aw) were inoculated with 1% v/w of single bacterial inoculum (including 4 Salmonella, 3 Listeria monocytogenes, 3 Escherichia coli O157:H7 and 4 non-pathogenic surrogates Enterococcus faecium, Escherichia coli P1, Escherichia.coli K12 and Listeria innocua), stored at 22 °C for 4 days to reach equilibrium and subjected to steam treatments at 70 and 75 °C for 5 min. Results indicated that steaming at 70 °C was sufficient to eliminate tested E. coli O157:H7 strains on black peppercorns at aw 0.57 and 0.69. Increased thermal resistance was observed on all pathogenic strains at the lowest aw 0.35 during treatments at 70 °C. Increasing the treatment temperature to 75 °C resulted in ≥ 5-log reductions of Salmonella and L. monocytogenes strains at all tested aw. Among the four surrogate strains, Enterococcus faecium was shown to be the most suitable surrogate in validating mild steaming processes of black peppercorns. Steaming conditions tested led to no color changes on treated black peppercorns (aw < 0.80) compared to the original ones. Mild steaming at 75 °C has the potential to be applied in the production of dried black peppercorns to lower the microbial contaminants while maintaining the product's visual quality. Additionally, data collected on the wide range of pathogenic strains in the present study regarding their survival on black peppercorns during storage (22 °C) and steam treatments demonstrate that Salmonella remained the pathogen of concern for dried food matrices.