Efficacy of gaseous chlorine dioxide (ClO2) treatment on quality parameters and against Listeria innocua growth on apple surfaces under controlled atmosphere (CA) storage condition and post-treatment quality analysis

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

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Apples are vulnerable to contamination with foodborne pathogens (i.e., Listeria monocytogenes) and spoilage microorganisms (i.e., yeasts and molds) during storage, especially long-term controlled atmosphere (CA) storage. The most significant risk to consumers is that there is no “kill step” included in the apple post-harvest packing process to eliminate pathogenic microorganisms. In 2014, caramel apples contaminated with L. monocytogenes were linked to a foodborne illness outbreak, which caused 35 people to contract listeriosis and 7 deaths. This addresses an urgent need to improve current food safety systems in the apple packing industry. Gaseous ClO2 has been identified as a potential intervention during apple cold storage that can be integrated into the CA processes to extend shelf life and inactivate foodborne pathogens. However, there is a knowledge gap on the antimicrobial efficacy of gaseous ClO2 under CA conditions. Lab-scale experiments are needed to prototype the integration of gaseous ClO2 into CA conditions on an industrial scale. Therefore this study studied the efficacy of gaseous ClO2 inactivation of L. innocua on fresh apple surfaces under CA conditions and evaluated the post-treatment influence of gaseous ClO2 on apple fruit quality after RA cold storage. As a result, gaseous ClO2 treatments killed L. innocua by more than 99.68% without damaging the quality of apples and may help to delay spoilage during storage.

Technical Abstract: Limited information is available regarding gaseous chlorine dioxide (ClO2) treatments against Listeria and spoilage microorganisms (MOs) on fresh apples under controlled atmosphere (CA) conditions. In this study, different amounts of dry precursors (initial inputs) of gaseous ClO2 in combination with CA storage were evaluated for their impact on fresh apple surfaces by measuring the inactivation of Listeria innocua (L. innocua), reduction of spoilage MOs, and quality changes. Gaseous ClO2 was generated by a sachet containing an equal amount of dry precursors (sodium chlorite and reducing acids) in a 45-L CA chamber. A cocktail of L. innocua was spot inoculated on the calyx of fresh Fuji apples and treated for 1 h with different initial inputs of ClO2 (1, 5, 10, 15, and 20 g of each precursor). For the storage study, non-inoculated fruits were treated simultaneously with gaseous ClO2 and then stored for 28 d at 4°C. The quality of treated apples during storage was measured at 1, 14, and 28 d. The spoilage MOs were measured post-treatment and at 28 d of storage. Headspace ClO2 concentrations, temperature, and relative humidity (RH) in the chambers were measured during the batch treatments. Gaseous ClO2 at 1, 5, 10, 15, and 20 g initial inputs for 1-h treatment achieved 0.81, 0.60, 1.36, 2.10, and 2.59 log CFU/mL reductions of L. innocua, respectively. After treatment, both total plate counts (TPC) and total yeasts and molds (TYM) were reduced at different inputs. Significant (p < 0.05) log reductions of TPC and TYM appeared at higher inputs (15 and 20 g). The population of TYM was higher after treatment plus storage than after treatment, which indicates that TYM recovered during storage than post-treatment. This also suggests that in order to continue suppressing spoilage MOs, gaseous ClO2 may be integrated into cold storage to sustain the suppression. Furthermore, the treatments did not have any significant (P > 0.05) effect on appearance, color, firmness, total soluble solids (TSS) or total soluble phenolic (TSP) content, and antioxidant (AOX) activity of apples during 28-d storage, except for the lenticel breakdown observed on 15 and 20 g treated apples after 28 d storage. Overall, gaseous ClO2 treatments that achieved more than 2.5 log reductions of L. innocua did not significantly (P > 0.05) damage the quality of apples and may help to delay spoilage during storage.