Limited surveys have isolated coliforms (Weinzirl, 1929) and E. coli ( Entis et al., 1984, Kokal, 1965, Little et al., 2009, Little et al., 2010, Meyer and Vaughn, 1969 and Riyaz-Ul-Hassan et al., 2003) from walnut kernels. Salmonella was isolated from walnut kernels in India (10 g, n = 50) ( Riyaz-Ul-Hassan et al., 2003) and from one pre-packed mixed nuts sample (25 g, n = 329) that also contained walnuts ( Little et al., 2010), but was not detected in other surveys that included walnut kernels (25 g, n = 74 ( Little et al., 2009); 25 g, n = 441 ( Little et al., 2010); 25 g, n = 80 ( NSW Food Authority, 2012)). In a 3-year survey of California inshell walnuts, E. coli O157:H7 was not detected; Salmonella

was detected in none of the samples in 2010 (100 g, n = 935), in 0.2% of samples in 2011 (375 g, n = 905), and in 0.1% C646 chemical structure of samples in 2012 (375 g, n = 999) ( Eidsath, 2012). The United States is the leading exporter of the Persian or English walnut (Juglans regia L.); 99% of the U.S. production (470,000 metric tons projected in 2012) is grown in California ( California Walnut Commission, 2012, [USDA FAS] U.S. Department of Agriculture, Foreign Agricultural

Service, 2012 and [USDA NASS] U.S. Department of Agriculture, National Agricultural Statistics Service, 2012). Shortly after harvest, walnuts are hulled to remove the fleshy husk and then dried with forced air; dried inshell walnuts may be stored prior to packaging or shelling. In Temozolomide order 2011, approximately 40% of edible California walnut kernels were sold in-the-shell (estimated average Resveratrol 44% kernel weight) and the majority of these inshell walnuts (94%) were exported ( California Walnut Board, 2012); the remaining 60% were removed from storage as needed, then cracked and sold as kernels. Traditionally, most of the inshell walnuts sold in North America undergo a shell-lightening (or “brightening”) treatment by direct surface application of sodium hypochlorite at a concentration

of 3 to 4% (30,000–40,000 μg/ml or ppm in solution). The solution is sprayed onto the nuts, which are then mechanically mixed for approximately 2 min in a barrel trommel, and dried with or without forced air (Lindsay, 2010). Although the purpose of this treatment is to lighten shells, sodium hypochlorite is also a common disinfectant; it is unknown to what extent brightening impacts the microbial load on walnut shells. The routes of contamination of tree nuts have not been definitively determined, but there are a number of potential opportunities for introduction of foodborne pathogens to walnuts through direct contact with contaminated soil during harvest, during postharvest hulling and drying, during cracking and shelling, or during further processing (Blessington, 2011, Meyer and Vaughn, 1969 and Weinzirl, 1929). Foodborne pathogens can survive for extended periods on walnut kernels (Blessington et al.