3.2. Influence of temperature and inoculum level on survival of Salmonella
Enteritidis PT 30 on inshell walnuts during storage
Inshell walnuts are typically stored in large silos or in warehouses in
bins. Temperatures during storage are often at ambient during the cooler
months after harvest; as ambient temperatures rise, walnuts may be
transferred to cold storage (4 to 10 °C) to reduce the potential for development
of rancidity. Inshell walnuts may also be stored, and are often
distributed and retailed, at ambient temperature.
Inshell walnuts were inoculated with Salmonella at approximately
10 log CFU/nut and dried for 24 h at ambient conditions; after drying,
population densities declined by 0.70 log CFU/nut to 9.5 log CFU/nut
(Table 1). The inoculated driedwalnutswere stored at 4 °C and ambient
conditions. At 21 days of storage and all subsequent sampling times,
Salmonella populations were significantly greater on walnuts stored at
4 °C (relative humidity ranged from 65 to 95%) than those stored
under ambient conditions (Fig. 1A). After 20 weeks (139 days), populations
onwalnuts stored at 4 °C or ambient had declined by 0.5 or 2.7 log
CFU/nut, respectively (Table 1, Fig. 1A). Although it is unusual for
walnuts to be stored for more than 1 year, Salmonella levels were also
determined on these nuts stored for 1.2 and 3.1 years (431 and
1143 days, respectively). After 1.2 and 3.1 years of storage, Salmonella