Sequential combination of gaseous chlorine dioxide and ultraviolet-C: Tackling sub-lethally stressed Salmonella enterica on raw whole almonds and fresh-cut leafy greens.

Sub-lethal stress can induce cross-protection in pathogens, complicating food processing. We evaluated the combined effects of chlorine dioxide (CD) and ultraviolet-C (UV-C) on sub-lethally stressed Salmonella enterica on raw whole almonds (RWAs) and fresh-cut leafy greens (FCLGs), post-treatment survival on FCLGs, and Enterococcus faecium NRRL B-2354 as a S. enterica surrogate. S. enterica cocktails (RWAs: S. Enteritidis, Newport, Typhimurium; FCLGs: S. Enteritidis Montevideo, Typhimurium) were subjected to desiccation, oxidation, heat shock, or acid stress. Stressed and unstressed S. enterica and NRRL B-2354 were inoculated onto RWAs and FCLGs, and treated with CD (0-0.6 mg/L, 0-30 min) or CD + UV-C [CD (0-0.4 mg/L, 0-15 min) followed by UV-C (254 nm, 0-450 mJ/cm2, 0-15 min)]. Treated FCLGs were stored under cold storage (4 °C) or temperature abuse (35 °C for 2 h, then 4 °C) for seven days. CD + UV-C produced < 5.6- and ≥ 5.6-log reductions on RWAs and FCLGs, respectively, while CD achieved < 2.0- and < 2.5-log reductions, respectively. Desiccation- or oxidation-stressed cells were more resistant (P < 0.05) than unstressed or other stressed cells. Treatment (CD vs. CD + UV-C) and microorganism (S. enterica vs. NRRL B-2354) were dominant factors influencing inactivation. Association rule mining identified CD + UV-C on S. enterica yielding high reductions. Stressed cells declined more rapidly under cold storage, while desiccation-stressed cells persisted under temperature abuse. NRRL B-2354 showed lower reductions than S. enterica (P < 0.05), supporting its use as a surrogate with safety margin. These results support CD + UV-C as an effective hurdle strategy and highlight the importance of stress adaptation in validating interventions.