Coating with phenolic branched-chain fatty acid reduces Listeria innocua populations on apple fruit

Authors: Ryu, Victor; Uknalis, Joseph; Ngo, Helen; Jin, Zhonglin; Fan, Xuetong

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2024
Publication Date: 5/15/2024
Citation: Ryu, V.N., Uknalis, J., Lew, H.N., Jin, Z.T., Fan, X. 2024. Coating with phenolic branched-chain fatty acid reduces Listeria innocua populations on apple fruit. International Journal of Food Microbiology. 419:110748. https://doi.org/10.1016/j.ijfoodmicro.2024.110748.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2024.110748

Interpretive Summary: In recent years, foodborne disease outbreaks and recalls have been linked with fresh apples due to Listeria monocytogenes contamination occurring during postharvest handling. In the present study, we have formulated an anti-listeria coating composition made from our patented bio-based antimicrobials, which are produced from fatty acids and natural phenolic compounds. When applied on apple fruit, the bio-based coating reduces the population of Listeria innocua, a surrogate of Listeria monocytogenes, by more than 99%. In addition, the coating preserves the freshness of apples during a simulated shelf-life study by reducing 36% of moisture loss. Therefore, the novel coating formulation provides for the apple industry a simple tool to minimize the risk of Listeria contamination while maintaining fruit quality.

Technical Abstract: This study focused on the potential of phenolic branched-chain fatty acid (PBC-FA) as an antimicrobial coating for the inactivation of Listeria, contributing to the preservation of apple quality. An antimicrobial coating was developed by blending PBC-FA with glycerol and carboxymethyl cellulose solution (CMC) at pH 7. The resulting PBC-FA-CMC solution formed a stable emulsion with an average droplet size of approximately 77 nm, maintaining stability for at least 30 days at 20°C. The in vitro antimicrobial efficacy of the film derived from the PBC-FA emulsion was assessed against a mixture of three strains of Listeria innocua (L.) with an initial population of 7 log CFU/mL. A film concentration of 1 mg/mL PBC-FA effectively reduced L. innocua populations below the detection limit (<1.48 log CFU/mL) in vitro. The antimicrobial effect of the 1 mg/mL PBC-FA-CMC coating formulation was further investigated against L. innocua inoculated on apples before and after coating. Comparative analysis with non-coated control samples revealed a reduction of approximately 2 log CFU/fruit and around 6 log CFU/fruit on TSA and PALCAM media, respectively. This suggests that the PBC-FA applied as a coating on apples caused injury to bacterial cells. When L. innocua was inoculated onto coated apples, populations decreased by approximately 4 log CFU/fruit during a 14-day storage period at 20°C. The PBC-FA coating exhibited the additional benefit of reducing moisture loss without affecting the color, firmness, and soluble solids content of apples during the storage period.