Effect of Humidity and Storage Temperature on the Survival of Salmonella in Paprika and Black Pepper

Introduction: Salmonella is an ongoing concern as a vehicle for foodborne outbreaks in low-moisture foods such as dried spices. It has been shown to persist for years during storage of spices.  However, recent publications indicate a dramatic effect of humidity and temperature on the survival of Salmonella during storage.  The exact relationship between temperature and humidity and their influence on the survival of Salmonella during spice storage has not been carefully examined.

Purpose: The objective of this study is to determine how prolonged storage at various temperatures and humidity levels affects the persistence of Salmonella in spice using paprika and ground black pepper as model spices. 

Methods: A cocktail of four different Salmonella serovars was inoculated at approximately 7-8 log CFU/g into 1 g samples of paprika or ground black pepper.  The samples were stored at different temperature (10, 25 and 37°C) and humidity (32, 43, 57 and 80 %) combinations for up to 2 years.  Survival was determined by a brief enrichment in tryptic soy broth with yeast extract followed by enumeration on both tryptic soy agar with yeast extract and xylose lysine desoxycholate agar. 

Results: Storage at 37°C resulted in a loss of detection of Salmonella at a more rapid rate when compared to lower temperatures.  As the humidity was increased at 37°C, Salmonella survival decreased from ~30 days (32% humidity) to only a matter of hours (80% humidity).   However, at the lower temperatures, Salmonella continued to persist with no remarkable decline in population even when combined with high humidity.  Statistically, a correlation between type of spice, storage temperature, relative humidity and survivability was established.

Significance: Results of this study indicate that storage temperature plays a greater role in the persistence of Salmonella in these low-moisture foods as compared to the humidity.