Survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on Inoculated Almonds and Pistachios Stored at −19, 4, and 24°C

Abstract

The survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was determined on almonds and pistachios held at typical storage temperatures. Almond kernels and inshell pistachios were inoculated with four- to six-strain cocktails of nalidixic acid-resistant Salmonella, E. coli O157:H7, or L. monocytogenes at 6 log CFU/g and then dried for 72 h. After drying, inoculated nuts were stored at -19, 4, or 24°C for up to 12 months. During the initial drying period after inoculation, levels of all pathogens declined by 1 to -log CFU/g on both almonds and pistachios. During storage, moisture content (4.8%) and water activity (0.4) of the almonds and pistachios were consistent at -19°C; increased slowly to 6% and 0.6, respectively, at 4°C; and fluctuated from 4 to 5% and 0.3 to 0.5 at 24°C, respectively. Every 1 or 2 months, levels of each pathogen were enumerated by plating; samples were enriched when levels fell below the limit of detection. No reduction in population level was observed at -19 or 4°C for either pathogen, with the exception of E. coli O157:H7-inoculated almonds stored at 4°C (decline of 0.09 log CFU/g/month). At 24°C, initial rates of decline were 0.20, 0.60, and 0.71 log CFU/g/month on almonds and 0.15, 0.35, and 0.86 log CFU/g/month on pistachios for Salmonella, E. coli O157:H7, and L. monocytogenes, respectively, but distinct tailing of the survival curves was noted for both E. coli O157:H7 and L. monocytogenes.

Modeling and Statistical Issues Related to Salmonella in Low Water Activity Foods

“…The influence of temperature began to show around day 30, after which a significant decline was observed for the data at 22°C, while no significant decline was observed at either −24 or 4°C (Figure 10.1). These observed survival kinetics for Salmonella on raw peanuts are in line with other published literature, where survival curves for Salmonella in low water activity foods do not follow log-linear kinetics and show significant asymptotic tails (Uesugi, Danyluk, and Harris, 2006;2010, Blessington, Mitcham, andKimber et al, 2012;Blessington et al, 2013a;Blessington et al, 2013b;Keller et al, 2013;Santillana Farakos, Frank, and Schaffner, 2013). The data presented in Figure 10.1 indicate that the best descrip tion of Salmonella survival under these conditions requires a model that includes a nonlinear inactivation rate and the ability to incorporate tailing.…”

Comparison of Desiccation Tolerance among Listeria monocytogenes, Escherichia coliO157:H7, Salmonella enterica, and Cronobacter sakazakii in Powdered Infant Formula

“…Listeriosis associated with the consumption of low-aw food containing Listeria monocytogenes has not been documented. However, L. monocytogenes has been detected in several types of dry foods (19,20). These bacterial pathogens can survive under dry or low-aw environments for long periods of time in or on various foods and food contact surfaces (4,19,20,33).…”

Microbial Safety of Low Water Activity Foods: Study of Simulated and Durban Household Samples

“…This indicates that a high sucrose content inhibits the growth of both these bacteria at slightly lower temperatures. Whilst limited studies implicate the presence of B. cereus and S. aureus, several have implicated the presence of E. coli and Salmonella [1,8,16,19,20] The macadamia butter used in this simulative study had a carbohydrate content of 5 g of which of total sugar amounted to 3,3 g per 100 g (3,3%). A similar trend was noticed in macadamia butter stored at 18 ∘ C despite the butter having the contained added sugar.…”