Differential Persistence and Survival of Salmonella Serovars in Spices with Low-water Activity

Introduction: Although Salmonella outbreaks from low-moisture products are relatively rare, they often impact large numbers of people. Spices represent one such vehicle for transmission to humans. Salmonella contamination of spices poses great risks to U.S. consumers since spices are often added just prior to consumption or are ingredients in RTE products.

Purpose: The purpose of this study was to determine the persistence and survival of Salmonella serovars in different varieties of spices at low water activity level. 

Methods: Salmonella serovars (Rissen, Anatum and Montevideo) were inoculated into black pepper, white pepper, ground cumin, and ground celery seed, respectively, at a starting level of 5 log CFU/g and incubated at ambient temperature (25°C) in a desiccator. The water activity in these spices remained low in the desiccator (a_w < 0.8). Culture populations were determined at day 0, 1, 2, 3, 4, 5, 6, 7, 14, 28, and 56 post inoculation (dpi).

Results: Although no growth of Salmonella was documented in spices at low water activity, Salmonella serovars can survive in certain spices for an extended period of time. The survival of Salmonella in spices is both serovar dependent and spice dependent. For example, in white pepper, all serovars showed a 2-log decrease after 24 h inoculation. While serovar Rissen was undetectable after 7 days, serovar Montevideo was able to be recovered continuously through 28 dpi.  Among all the varieties of spices investigated, all Salmonella serovars survived better in ground cumin than other spice vehicles.

Significance: Certain Salmonella serovars can survive in spices even at low water activity level and may persist for an extended period of time.  Pinpointing specific growth dynamics of Salmonella adapted to persist in various spice substrates will aid in assigning more accurate microbiological risk assessments to this important and widespread food group.