Investigation of methods for inactivating foodborne pathogens in black pepper

Abstract

This study evaluated the efficacy of the simultaneous application of NIRUV (Near-infrared and Ultraviolet light) with organic acid (OA), peracetic acid (PAA) and Carvacrol (CAR) treatment for inactivating food-borne pathogens, including E. coli O157:H7 and S. Typhimurium on black pepper. A cocktail of three strains of Escherichia coli O157:H7 (ATCC 35150, ATCC 43889, ATCC 43890) and Salmonella Typhimurium (ATCC 19585, ATCC 43971, DT014) was inoculated onto black pepper and then treated by spraying with organic acid (2 % malic acid, 2 % citric acid), 80 ppm peracetic acid or 1 mM carvacrol and exposing to NIRUV for 7 min. A quartz halogen infrared heating lamp (radiation intensity, 141.75 μW/cm2/nm at the sample location) and a UV germicidal lamp (radiation intensity, 2.62 mW/cm2 at the sample location) were used. Also, the effect of the treatment on quality was determined by measuring changes in color. NIRUV treatment for 7 min achieved approximately 2 log CFU reductions in E. coli O157:H7 and S. Typhimurium. Organic acid (malic acid, citric acid) and peroxyacetic acid treatment with NIRUV for 7 min showed approximately 3 log CFU reductions of E. coli O157:H7 and S. Typhimurium. After 1 min, E. coli O157:H7 and S. Typhimurium treated by the carvacrol and NIRUV were not detected. The inactivation mechanisms were evaluated by the propidium iodide (PI) uptake test and transmission electron microscopy (TEM) analysis. The result of PI uptake and that of TEM showed similar patterns. NIRUV-combined treatment caused disruption of the bacterial cell membrane and cell wall. Moreover, NIRUV-CAR treatment showed severe cell disruption. These results mean that major factor of synergistic lethal effect was cell membrane damage. Ialso measured quality of black pepper treated by each combination treatment. The color values of the NIRUV combined treatment were not significantly (P > 0.05) different from those of the control. In case of the injured cell, the value of microbial cell and that of injured cell were not significantly (P > 0.05) different. These results suggests that NIRUV and OA, PAA, CAR combined treatment can be applied as an alternative to other interventions for spices. In conclusion, NIRUV-combined system can be expanded to food industry because of its safety and easy utility.