Comparing thermal resistance of Salmonella in chili (Capsicum), cinnamon (Cinnamomum cassia), and black pepper (Piper nigrum) powders

Thermal treatment is one of the most effective methods used in the food industry for pathogen control in low-moisture foods. The water activity (a_w) at treatment temperatures, not room temperature, is an important factor influencing microbial thermal resistance. This study evaluated the thermal resistance of a three-strain Salmonella cocktail in chili, cinnamon, and black pepper powders that had been pre-conditioned to room temperature a_w of 0.30 or 0.50 (i.e., a_w,21°C = 0.3 and 0.5). a_w of these samples increased differently in sealed containers when they were heated from 20 to 90 °C. Regardless of spice type, Salmonella thermal resistance decreased with increasing a_w. In chili, the observed D_70°C-values (the time required to inactivate 90% cells at a given temperature) for Salmonella in the samples of a_w,21°C 0.30 (a_w,70°C 0.35) was 15.4 min and in the samples of a_w,21°C 0.50 (a_w,70°C 0.52) was 1.8 min. At the same a_w,21°C, the observed D-values of Salmonella in chili and cinnamon were significantly (P <0.05) lower than in black pepper. However, based on a_w at treatment temperatures, Salmonella showed similar thermal resistance in cinnamon and black pepper but was less resistant in chili. The findings highlight the importance of a_w at treatment-temperature in determining microbial thermal resistance and suggest that milder temperatures may be sufficient for Salmonella control in chili powder.