Effects of moisture content and mild heat on the ability of gaseous chlorine dioxide against salmonella and enterococcus faecium NRRL B-2354 on almonds

Authors: RANE, BHARGAVI - Washington State University; Lacombe, Alison; SABLANI, SHYAM - Washington State University; Bridges, David; TANG, JUMING - Washington State University; GUAN, JIEWEN - Washington State University; Wu, Vivian

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2020
Publication Date: 10/27/2020
Citation: Rane, B., Lacombe, A.C., Sablani, S., Bridges, D.F., Tang, J., Guan, J., Wu, V.C. 2021. Effects of moisture content and mild heat on the ability of gaseous chlorine dioxide against salmonella and enterococcus faecium NRRL B-2354 on almonds. Food Control. 123. Article 107732. https://doi.org/10.1016/j.foodcont.2020.107732.
DOI: https://doi.org/10.1016/j.foodcont.2020.107732

Interpretive Summary: In order to use bacterial surrogates as representatives for pathogens in industrial facilities during treatments, respective surrogates need to be validated. For this, treatments were done on almonds containing a foodborne pathogen and its surrogate. Post-treatment results showed that ClO2 achieved an increase in the bacterial reductions on almonds after the addition of moisture and heat during treatments compared to ClO2 alone. The results indicate the importance of added moisture on almond surfaces and mild heat during gaseous chlorine dioxide (ClO2) treatments on almonds. In conclusion, gaseous ClO2 can be used in combination with moisture in the almond processing to enhance food safety.

Technical Abstract: Contamination of almonds with pathogenic Salmonella can be detrimental to consumer’s health and deterioration of the product. This study evaluated the influence of increased moisture content (MC) and mild heat on gaseous chlorine dioxide (ClO2) to inactivate microorganisms, using almonds. Almonds were inoculated with pathogenic Salmonella enterica and nonpathogenic surrogate Enterococcus faecium NRRL B-2354. A dry precursor method was used to produce gaseous ClO2 to treat almonds in an airtight desiccator chamber. A 20-g precursor amount produced a dose of 1.34 mg/L gas over 4 h in the empty chamber. Gaseous ClO2 was used to treat almonds with, (i) original moisture content (MC, 4%), (ii) increased MC (7%), and (iii) increased MC (7%) and mild heat (40 oC). Post-ClO2 treatment results demonstrated bacterial reductions of 1.2 log CFU/g on Salmonella at 3 h and 0.9 log CFU/g on E. faecium inoculated almonds at 4h. Gas treatment with the addition of moisture (3% added on almonds) provided bacterial log reductions of 1.8 CFU/g on Salmonella and 1.0 CFU/g on E. faecium inoculated almonds at 3 h. Gaseous ClO2 with moisture and heat provided the highest bacterial reduction on almonds at 3 h (2.0 CFU/g on Salmonella and 1.6 on E. faecium). Bacterial reduction observed on Salmonella was statistically (P < 0.05) similar to E. faecium. Scanning electron microscopy (SEM) analysis displayed the complex 3-dimensional surface of almonds in comparison to coupons. Bacterial cells were observed to be covered in lipids and settled in crevices on almond surfaces. This study demonstrated the importance of moisture and heat for the application of gaseous ClO2 on almonds. The application of this technology can be suitable to address the cross-contamination problems faced by the food industry for the safety of almonds.