Use of a silver-based sanitizer to accelerate Escherichia coli die-off on fresh-cut lettuce and maintain produce quality during cold storage: Laboratory and pilot-plant scale tests

Authors: MENDES-OLIVEIRA, GABRIELLA - Orise Fellow; Luo, Yaguang - Sunny; ZHOU, BIN - University Of Maryland; TENG, ZI - University Of Maryland; BOLTEN, SAMANTHA - Orise Fellow; Park, Eunhee; Pearlstein, Daniel; Turner, Ellen; Millner, Patricia; Nou, Xiangwu

Submitted to: Food Research International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2021
Publication Date: 3/26/2022
Citation: Mendes-Oliveira, G., Luo, Y., Zhou, B., Teng, Z., Bolten, S., Park, E., Pearlstein, D.J., Turner, E.R., Millner, P.D., Nou, X. 2022. Use of a silver-based sanitizer to accelerate Escherichia coli die-off on fresh-cut lettuce and maintain produce quality during cold storage: Laboratory and pilot-plant scale tests. Food Research International. https://doi.org/10.1016/j.foodres.2022.111170.
DOI: https://doi.org/10.1016/j.foodres.2022.111170

Interpretive Summary: The leafy greens fresh-cut industry needs and continues to pursue additional technologies and practices to reduce the risk of product contamination by foodborne illness pathogens. Effective technologies must also maintain product quality to meet consumer acceptability during refrigerated storage. In a series of studies, the effects of a novel process aid containing silver dihydrogen citrate, glycerin, and lactic acid (SGL) were evaluated on fresh-cut romaine and iceberg lettuce inoculated with Escherichia coli O157:H7 or Listeria monocytogenes after flume washing, and during cold storage. Results of this study show that this new technology has the potential to hasten E. coli die-off on fresh-cut lettuce during cold storage and improve product safety. In addition, results show that flume washing eliminates residue of the process aid on flume washed lettuce and that final product quality and shelf life are unaffected. These findings will benefit fresh-cut lettuce processors in their efforts to enhance pathogen inactivation.

Technical Abstract: Outbreaks involving romaine and iceberg lettuce are frequently reported in the United States. Novel technologies are needed to inactivate pathogens without compromising product quality and shelf-life. The objective of this study was to evaluate the effects of a novel process aid composed of silver dihydrogen citrate, glycerin, and lactic acid (SGL) on Escherichia coli and Listeria monocytogenes on inoculated lettuce immediately after washing and during cold storage. Sensory and quality attributes of fresh-cut iceberg lettuce were also evaluated. This study consisted of two stages: (1) laboratory scale testing, and (2) pilot-plant confirmation, with prospective SGL residual investigation and lettuce quality and shelf life evaluation. Laboratory results indicated that application of SGL solution for 30 second as a first step in the washing process resulted in a 3.15 log reduction in E. coli O157:H7 immediately after washing. A significant difference between SGL treatment and the control was maintained until day 7. Pilot-plant results showed that samples receiving SGL spray followed by chlorinated flume wash exhibited a greater reduction (1.48 log) in E. coli population at the end of shelf life than other treatments (p<0.05). Additional pilot plant tests were conducted to determine concentrations of SGL residual solution in the final washed lettuce. Results show that the SGL solution leaves no residue on flume washed lettuce samples. The final quality and shelf life of washed lettuce were unaffected by application of SGL after the process aid residues were removed by washing in the flume tank. In conclusion, the results of this study demonstrate that this new technology has the potential to accelerate E. coli die-off on fresh-cut lettuce during cold storage and improve product safety, while not affecting quality throughout the shelf life of the finished products.