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Retention of Viability of Salmonella in Sucrose as Affected by Type of Inoculum, Water Activity, and Storage Temperature

Salmonella has been detected in commercially manufactured high-sugar, low-water activity foods.  Outbreaks of salmonellosis have been associated with consumption of high-sugar foods stored for several months after manufacture.  Rates of inactivation of Salmonella in several high-sugar foods have been reported, but factors affecting survival in sucrose in the absence of other food components has not been described.  The objective of this study was to determine the effect of aw and storage temperature on survival of Salmonella in dry- and wet-inoculated sucrose.

Food-grade sucrose (aw 0.24 - 0.26 and aw 0.44 - 0.54) dry- and wet-inoculated with low (2.3 - 2.9 log CFU/g) and high (5.2 - 5.8 log CFU/g) populations of a five-serotype mixture of Salmonella was stored at 5°C and 25°C for up to 36 wk.  Duplicate samples representing all combinations of test parameters in two independent trials were analyzed for the presence (by enrichment) and number of Salmonella surviving for 0, 1, 3, 12, 18, 26 (dry inoculum), 28 (wet inoculum), and 36 wk.

Initial high counts in dry-inoculated sucrose stored at 5°C for 36 wk decreased by 0.7 log CFU/g.  In contrast, initial high counts in sucrose stored at 25°C decreased by 3.7 to > 4.2 log CFU/g within 36 wk. Survival of Salmonella was not markedly affected by aw.  Inactivation rates in wet-inoculated sucrose were similar to those in dry-inoculated sucrose; however, a trend toward higher persistence of Salmonella in dry- versus wet-inoculated sucrose suggests there was a higher proportion of cells in the wet inoculum with low tolerance to osmotic shock. Survival patterns in sucrose initially containing a low number of Salmonella were similar to those in sucrose initially containing a high population.  The pathogen survived in low-inoculum sucrose stored at 5°C for 36 wk, regardless of aw or type of inoculum, and in dry-inoculated sucrose (aw 0.54) and wet-inoculated sucrose (aw 0.24) stored at 25°C for up to 12 and 26 wk, respectively.

Sucrose may become contaminated with Salmonella during handling and transport, and in storage areas in food manufacturing facilities.  The ability of Salmonella to survive in sucrose for extended periods of time highlights the need to prevent post-processing contamination.  Consideration should be given to routinely monitoring sucrose for the presence of Salmonella, particularly if it is intended for use as an ingredient in foods not receiving a treatment that would be lethal to the pathogen.