Factors Affecting Infiltration and Survival of Salmonella on In-Shell Pecans and Pecan Nutmeats

Abstract

A study was done to determine the infiltration and survival characteristics of Salmonella in pecans. The rate of infiltration of water into in-shell nuts varied among six varieties evaluated and was significantly (α = 0.05) affected by the extent of shell damage. The rate of infiltration at −20 or 4°C was lower than the rate of infiltration into nuts at 21 or 37°C when nuts were immersed in water at 21°C. In-shell nuts immersed in a suspension of Salmonella (8.66 or 2.82 log CFU/ml) for 1 h contained populations of 6.94 to 6.99 and 1.85 to 1.95 log CFU/g, respectively. Salmonella that infiltrated in-shell nuts reached the kernel and remained viable after drying and during subsequent storage at 4°C. Initially high (5.78 log CFU/g) and low (1.53 log CFU/g) populations of Salmonella did not significantly decrease in in-shell pecans stored at −20 and 4°C for 78 weeks (18 months). Significant reductions of 2.49 and 3.29 log CFU/g occurred in in-shell nuts stored for 78 weeks at 21 and 37°C, respectively. High (6.16 log CFU/g) and low (2.56 log CFU/g) populations on pecan halves and high (7.13 log CFU/g) and low (4.71 log CFU/g) populations on medium pieces stored for 52 weeks at −20 and 4°C decreased slightly, but not always significantly. Significant reductions occurred on nutmeats stored for 52 weeks at 21 and 37°C, but the pathogen was detectable, regardless of the initial inoculum level. Results emphasize the importance of applying process treatments that will inactivate Salmonella.