Destroy Salmonella on raw almonds with high pressure.

Raw whole almonds have emerged as a source of S. enteriditis infection. In 2001, raw almonds were linked to an outbreak of S. enteriditis which had a rare phage type--PT30. This rare type aided in the identification of the outbreak strain. In 2004, another outbreak of a rare phage type of S. enteriditis--PT9C--was found to be caused by contaminated raw almonds.

These outbreaks of salmonellosis show how important it is to have effective processing methods that can control the pathogen's growth on raw almonds without destroying the texture and sensory attributes of the product. Scientists at the University of Wyoming investigated the ability of hydrostatic pressure (HP) to reduce the concentration of Salmonella on raw almonds. They found that the HP processing of certain dry foods is feasible if the product is directly suspended in the pressurizing medium--water.

In experiments, the researchers evaluated the effects of continuous and discontinuous (oscillatory) HP on the viability of two strains of S. enteriditis in pure culture and inoculated onto raw almonds, at 25 C, 50 C and 55 C.

The treatment completely inactivated S. enteriditis in 0.1% peptone water after continuous pressurization at 60,000 psi and 25 C for 5 minutes. The continuous pressurization of raw almonds inoculated with S. enteriditis at 60,000 psi and 50 C for 5 minutes resulted in less than a 1-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 almonds' low water activity imparted baroprotective attributes to the S. enteriditis cells. But when the almonds were directly suspended in water and then pressurized, the researchers achieved a log10 reduction of approximately 3.37.

Further information. John Willford, Department of Animal Science, University of Wyoming, Department 3684, 1000 E. University Ave., Laramie, WY 82071; phone: [phone]; fax: [phone]; email: [e-mail].