Potential use of supercritical carbon dioxide to decontaminate Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium in alfalfa sprouted seeds

Abstract

We sought to develop a method of decontaminating alfalfa sprouts of Escherichia coli O157:H7. Listeria monocytogenes. and Salmonella typhimurium without altering the seed germination capability using supercritical carbon dioxide (SC-CO2). Samples were treated with SC-CO2 at 10, 15, or 20 MPa and temperatures of 35, 40, or 45 degrees C for 5, 10, or 15 min. The germination percentage was measured after three days of germination. Generally, treating seeds with SC-CO2 at higher pressures, temperatures, or for longer treatment times resulted in greater microbial reductions than treatments at lower pressures, temperatures, or for shorter treatment times. SC-CO2 treatment clearly reduced the microorganism levels in alfalfa seeds; in particular, treatment at 20 MPa and 45 degrees C for 15 min reduced levels of the three pathogens by >7.0 log colony forming units (CFU)/g. However, SC-CO2 treatment at a high pressure and high temperature, especially treatment at 20 MPa and 40 or 45 degrees C, impaired the seed germination capability in some cases. Without impairing the germination capability, the maximum reduction level of E. coli O157:H7 was 3.51 CFU/g with SC-CO2 treatment at 15 MPa and 35 degrees C for 10 min. Maximum reductions of L monocytogenes and S. typhimurium were 2.65 and 2.48 log CFU/g, respectively, with treatment at 10 MPa and 45 degrees C for 5 min. Therefore, our results indicate that SC-CO2 treatment can be used to effectively improve alfalfa seed safety. (C) 2009 Elsevier B.V. All rights reserved.