Inactivation of Bacillus cereus Spores on Red Chili Peppers by Combined Treatments of Aqueous Chlorine or Chlorine Dioxide and Heat Drying

Introduction: Chili pepper or chili powder is easily contaminated with various microorganisms from postharvest to distribution and Bacillus spp. has been frequently isolated from them.

Purpose: We determined effect of combined treatments of aqueous chlorine or chlorine dioxide and heat drying on inactivation of B. cereus spores on red chili peppers.

Methods: Ten samples [half of pepper (Capsicum annuum L.)] washed and dried were inoculated with 4 - 5 drops of B. cereus spore suspension). Each samples were washed with sterile distilled water, aqueous chlorine (0, 50, 100, 200 ppm) or chlorine dioxide (50, 100 or 200 ppm) for 1 min and air-dried (25 ± 1°C, 47 ± 1% RH). The samples were then heat-dried at 55°C for up to 48 h. During the drying, populations of spores on samples were enumerated and a_w values and color of the samples were also measured every 12 h.

Results: The results showed that initial spore numbers (6.2 log CFU/sample) decreased to 4.4, 4.8, 3.8, 2.9, and 2.7 log CFU/sample immediately after washing with sterile water and 0, 50, 100, and 200 ppm of aqueous chlorine, respectively. After 12 h of drying, the populations of spores on samples washed with 100 or 200 ppm of aqueous chlorine reduced to < 2.0 log CFU/sample.  Initial spore numbers (6.4 log CFU/sample) decreased to 4.9, 5.4, 4.3, and 4.1 log CFU/sample immediately after washing with sterile water and 50, 100, and 200 ppm of chlorine dioxide, respectively. Treatments of red chili peppers with aqueous chlorine or chlorine dioxide prior to drying did not cause changes in a_w values and colors of dried chili peppers.

Significance: More rapid reduction rates in population of spores occurred on pepper samples washed with higher concentration of aqueous chlorine, whereas concentrations of aqueous chlorine dioxide did not cause different reduction rates on spore numbers on samples.