Radio frequency inactivation of E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 in black pepper (piper nigrum) kernels: Thermal inactivation kinetic study and quality evaluation

Abstract

In recent years, E. coli O157: H7 and Salmonella Typhimurium outbreaks in black peppers have caused intestinal diseases among human being, which calls for emergence of pasteurization processes for black pepper. Radio frequency (RF) energy has the potential of pasteurizing low moisture spices within a short time. In this study, thermal inactivation kinetics studies of E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 on black pepper kernels were conducted, respectively. Then, RF inactivation experiments were conducted on inoculated black pepper kernels to achieve the required lethality. Results showed the number of log reduction for E. coli O157: H7 was > 6 log CFU/g after 7.0 min when heating to 90 °C in RF. Meanwhile, Salmonella Typhimurium ATCC 14028 reached > 6 log CFU/g reduction after 8.0 min RF heating and reaching 100 °C. From the quality point of view, the residual amount of Caryophyllene, 3-Carene, d-Limonene, β-Pinene in black pepper after RF pasteurization was 0.0060, 0.0038, 0.0034, 0.0016 mg/g, respectively. Comparatively, after steam pasteurization, Caryophyllene, 3-Carene, d-Limonene, β-Pinene content in black pepper was 0.0043, 0.0023, 0.0020, 0.0009 mg/g, respectively. Compared with steam heating, flavor substances in black pepper were better retained after RF heating. Thus, RF heating could effectively inactivate E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 without significant influence on the quality of black pepper kernels.