Gaseous chlorine dioxide for inactivating Salmonella enterica and Enterococcus faecium NRRL B-2354 on chia seeds

Consumer awareness on health benefits of chia seeds has led to the increased consumption including in its raw form. As chia seeds are preferably soaked in water overnight before consumption, prior contamination with Salmonella can enhance the microbial load during soaking as the pathogens are provided with a high nutrition environment. In the present study, the antimicrobial efficacy of chlorine dioxide (ClO2) gas was evaluated for decontaminating Salmonella enterica in chia seeds and to determine if E. faecium can be a suitable surrogate for Salmonella enterica in validation studies. Chia seed samples were inoculated either with a cocktail of five S. enterica serovars or with E. faecium. The efficacy of ClO2 gas was evaluated at different concentration (5.0, 7.5 and 10.0 mg/L) and relative humidity (60, 70 and 80%) conditions exposed for 1-5 h. Reduction of both the bacterial populations was significantly influenced by ClO2 gas concentration, RH, and exposure time. At a gas concentration of 10 mg/L and 80% RH over a 5 h exposure period, Salmonella and E. faecium populations were reduced by 3.7 +/- 0.2 and 3.2 +/- 0.3 log CFU/g, respectively. Lower log reduction of E. faecium at treatment conditions achieving higher reduction (>2.5 log CFU/g) suggested its suitability as a surrogate for Salmonella during validation studies in chia seeds. Color, fatty acid composition, and germination capacity of treated chia seeds were not significantly impacted except for peroxide value which increased post gaseous treatment. The ClO2 byproducts in treated chia seeds were significantly higher than control; however, the chlorite concentration was below the maximum permissible levels in drinking water and therefore can be rendered safe.