P2-112 Survival of Salmonella during Storage on Three Different Tree Nut Varieties at Three Temperatures and Two Different Relative Humidity Levels

Tuesday, August 2, 2016
America's Center - St. Louis
Susanne Keller, U.S. Food and Drug Administration, Bedford Park, IL
Sofia Santillana-Farakos, U.S. Food and Drug Administration, CFSAN, College Park, MD
Regis Pouillot, U.S. Food and Drug Administration-CFSAN, College Park, MD
Introduction: Salmonella has been documented to survive for extended periods of time on almonds and pecans, but extrinsic factors such as temperature, and humidity of storage have not been thoroughly examined. 

Purpose: This study was conducted to examine the effect of temperature and humidity of storage on the survival of Salmonella on three different varieties of tree nuts. 

Methods: Three different tree nut varieties - pecans, hazel nuts and pine nuts - were chosen for examination based on differences in their typical fat content. Five different serotypes of Salmonella were grown to stationary phase on trypticase soy agar supplemented with 0.6% yeast extract and harvested for use as inoculum for each tree nut variety. Inoculated nuts were stored at 4, 10, and 25°C at two different humidity levels (57% RH and 34% RH). Each nut variety at each storage condition was monitored for one year by periodically removing 10-g quantities for testing for surviving Salmonella populations (plating on selective and non-selective media) and water activity. 

Results: Salmonella populations were reasonably stable at both humidity levels when stored at 4 and 10°C with a less than 1.5 log CFU/g population loss over the entire year tested. Population changes were detected at 25°C, with larger changes occurring at the higher humidity used. There was a significant difference (P < 0.0001) based on the variety of nut, with pine nuts showing approximately a 2 log CFU/g decline in Salmonella populations at 25°C and 57% RH versus 3.5 to 4-log decline under the same conditions for hazel nuts and pecans.

Significance: Differences in Salmonella survival on the different tree nut varieties may result in differences in the risk of illness associated with the consumption of these different nut varieties.