Effects of temperature, pH, and controlled water activity on inactivation of spores of Bacillus cereus in paprika powder by near-IR radiation

A process to decontaminate paprika powder using variable near-infrared (IR) radiation was tested using a closed sample holder allowing water to be retained in the powder. The reduction in the concentration of Bacillus cereus spores and changes in water activity ( a w) and colour were measured during IR heating. High heat flux was applied initially to heat the powder rapidly to the desired temperature, followed by low heat flux to maintain the temperature for a given time. The water activity ( a w) value of the powder could be maintained within the bulk of the closed sample, but the surface a w value decreased during heating. Due to carotenoid sensitivity to temperature, surface and overall colour values declined, though remaining acceptable values of medium red and red, respectively. For powder with an a w value of 0.88 heated to 95–100 °C, the load of B. cereus spores was reduced by 4.5 log 10 CFU/g within 6 min; the final spore concentration remained approximately 2 log 10 CFU/g due to tailing. Reducing pH to 4.0 from 4.5 did not significantly affect the reduction of the B. cereus spore concentration.