Survival of Salmonella in Snack Sandwiches

March 2015

Low-aw fillings in cookie and cracker snack sandwiches have not been considered as likely vehicles of foodborne pathogens. An outbreak of salmonellosis associated with a marshmallow confectionery and observations that Salmonella can survive for 8 months or more in fondant, halva, and dried fruits, however, have raised interest in learning more about its survival in high-sugar products.

We did a study to determine the rate of inactivation of Salmonella in dry- and wet-inoculated crème and non-crème fillings in cookie and cracker sandwiches, respectively, stored at 25°C (77°F) for up to 182 days (6 months). The time required for equilibration of aw of fillings and cookie or cracker components of sandwiches was determined.

Two cookie bases (chocolate and vanilla) and cheese crackers, along with high-sugar chocolate and peanut butter-based crème cookie fillings and peanut butter- and cheese-based cracker fillings, were obtained from commercial sources. Fillings and sandwiches containing fillings that had been dry-inoculated with Salmonella at high and low levels were stored at 25°C for 1, 6, 21, 35, 70, 112 and 182 days. Sandwiches were analyzed for populations and presence (by enrichment) of Salmonella. The aw values of the cookie base, cracker base, and filling components of sandwiches stored at 25°C for up to 80 days were measured.

At initial populations of 3.4 and 3.6 log CFU/g of chocolate crème and peanut butter crème cookie sandwiches, Salmonella survived for at least 182 days; initially at 0.38 log CFU/g, the pathogen survived for 35 and 70 days, respectively. Initially at 2.9 and 3.4 log CFU/g of cracker sandwiches containing peanut butter- and cheese-based fillings, respectively, Salmonella survived for 182 and 112 days; initially at 0.24 log CFU/g, the pathogen survived in cracker sandwiches containing peanut butter-based and cheese-based fillings for 1 and 35 days, respectively. Inactivation was more rapid in wet-inoculated peanut butter crème filling than in dry-inoculated filling, but unaffected by type of inoculum in peanut butter-based filling.

Chocolate cookie base (aw 0.39) and chocolate crème filling (aw 0.30) components of sandwiches equilibrated at aw 0.38 within 15 days; vanilla cookie base (aw 0.21) and peanut butter-based crème filling (aw 0.24) equilibrated to aw 0.24 between 50 and 80 days. Cheese cracker (aw 0.14) and peanut butter-based filling (aw 0.31) or cheese-based filling (aw 0.33) components of sandwiches equilibrated to aw 0.33 in 80 days.

The ability of Salmonella to survive for up to 182 days (6 months) in cookie and cracker sandwich fillings demonstrates a need to assure that filling ingredients do not contain the pathogen and contamination does not occur during manufacturing.