Destroy S. enteriditis on raw almonds using hydrostatic pressure processing.

Raw whole almonds have emerged as a source of S. enteriditis infection. In 2001, raw almonds were linked to an outbreak of S. enteriditis. The S. enteriditis had a rare phage type (PT30), which aided in identifying the outbreak strain. In 2004, a second outbreak was identified of a rare phage type of S. enteriditis (PT9C).

The recent outbreaks of salmonellosis caused by contaminated raw almonds have necessitated the development of effective processing methods that can control pathogen growth on raw almonds. But any such technique must not destroy the texture and sensory attributes of raw almonds.

Scientists at the University of Wyoming investigated the ability of hydrostatic pressure processing (HPP) to reduce the concentration of Salmonella on raw almonds. The HPP of certain dry foods is feasible if the product is directly suspended in the pressurizing medium (water).

The researchers examined the effects of continuous and discontinuous (oscillatory) HPP treatments on the viability of two S. enteriditis strains in pure culture, and inoculated onto raw almonds, at 25 C, 50 C and 55 C. Complete inactivation of S. enteriditis was achieved in 0.1% peptone water after continuous pressurization at 60,000 psi and 25 C for 5 minutes. Continuous pressurization of raw almonds inoculated with S. enteriditis at 60,000 psi and 50 C for 5 min resulted in less than a log reduction of vegetative cells.

A discontinuous process consisting of six cycles of pressurization at 60,000 psi and 50 C for 20 seconds provided slightly greater than a 1-log reduction of the S. enteriditis concentration. The low water activity (aW) of the almonds imparted baroprotective attributes to the S. enteriditis cells. When the almonds were directly suspended in water and then pressurized, a 10-log reduction was achieved.

Further information. John Willford, Department of Microbiology, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071; phone: [phone]; email: [e-mail].