Effect of high-pressure processing on microbial inactivation in açaí juices with varying pH and soluble solids content

Açaí juice pasteurization, high pressure processing, Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes

This study evaluated microbial inactivation effects of high-pressure processing (HPP) applied to açaí juices formulated with varying pH and soluble solids content (SSC). Açaí juice with pH 4.3 and 2.9 oBrix was initially inoculated with cocktails of 5 strains of E. coli O157:H7, Listeria monocytogenes or Salmonella spp. and processed at varying pressures (300, 400 and 600 MPa) and dwelling times (1 and 3 min) at 5 °C. The lethality at 400 MPa for 3 min was > 6-log CFU/mL. Further inactivation was observed during storage under refrigeration in the populations of Salmonella spp. and L. monocytogenes. In order to study the influence of pH and SSC on inactivation of Salmonella spp. by HPP, pH of açaí juice samples was adjusted to a range between 4.0 to 5.5 and SSC was adjusted between 2.9 to 14.9 oBrix. The ability of HPP to provide a 5-log reduction in the population of Salmonella spp. was reduced with increasing pH and SSC. Immediately after HPP the juices with pH 4.0 and 2.9 oBrix presented > 6-log reduction while the one with 8.9 oBrix resulted in 6-log reduction. In one week of refrigerated storage, the juices (pH 4.0-14.9 oBrix and pH 4.5-2.9 oBrix) also presented > 6-log reduction in Salmonella spp. concentration. These results indicate that a less intense process (below commonly recommended commercial conditions - 600 MPa/3 min) could be applied for açaí juice thus assuring required safety, in addition to an extra microbial inactivation verified during refrigerated storage.