Efficacy of low energy electron beam on microbial decontamination of spices

Abstract

Electrons with energies of 300 keV or lower have the potential to decontaminate the surfaces of various types of food products with minimal loss of quality. The aim of presented work was to determine the effectiveness of the process when applied to naturally contaminated food samples. Black pepper, white pepper and allspice samples were irradiated using electron beam at energy of 300 keV (low energy e-beam) and 10 MeV (high energy e-beam) to confirm the inactivation of bacteria. Total aerobic bacteria were counted before and after the irradiation and bacterial species were determined by a microbial identification system based on MALDI-TOF mass spectrometry. The range of applied low energy electron beam in food products estimated based on the depth-dose profile of electron beam and density of samples was about 300 μm thick. The log reduction in the total number of aerobic bacteria for spices samples irradiated with the high energy e-beam was comparable with that of the low energy e-beam, if estimated doses delivered on the surface were equivalent. (The log reduction by irradiation with 300 keV e-beam for 5 min corresponded to that by ca. 6 kGy irradiation with 10 MeV e-beam in conditions employed in this study). In non-irradiated spices, the dominant species was Bacillus subtilis. In irradiation of black pepper, the dominated species that survived after the irradiation were Cronobacter sakazaki and Bacillus megaterium, regardless of the energy of the electron beam. The effectiveness of microbial decontamination by both the low and the high energy e-beams was comparable for spices, where microorganisms exist in the surface layer. This study suggests the low energy e-beam as an alternative technology for the currently used highly penetrating ionising irradiation to eliminate microbial contamination of spices.