Salmonella inactivation and sponge/microfiber mediated cross-contamination during papaya wash with chlorine or peracetic acid as sanitizer

Authors: GU, GANYU - Orise Fellow; BOLTEN, SAMANTHA - Orise Fellow; MENDES-OLIVEIRA, GABRIELLA - Orise Fellow; Zhou, Bin; TENG, ZI - University Of Maryland; PEARLSTEIN, DANIEL - Orise Fellow; Luo, Yaguang - Sunny; Millner, Patricia; Nou, Xiangwu

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2020
Publication Date: 11/10/2020
Citation: Gu, G., Bolten, S., Mendes-Oliveira, G., Zhou, B., Teng, Z., Pearlstein, D., Luo, Y., Millner, P.D., Nou, X. 2020. Salmonella inactivation and sponge/microfiber mediated cross-contamination during papaya wash with chlorine or peracetic acid as sanitizer. Postharvest Biology and Technology. https://doi.org/10.1016/j.fm.2020.103677.
DOI: https://doi.org/10.1016/j.fm.2020.103677

Interpretive Summary: Contaminated papayas imported from Mexico are linked to several Salmonella outbreaks in recently years, raising significant public health concerns. In collaboration with leading industry associations (United Fresh Produce Association, Texas International Produce Association), USDA ARS scientists examined the risks of Salmonella contamination of papaya during postharvest washing and cleaning, especially the role of sponge or microfiber wash mitt in mediating Salmonella cross-contamination. The findings indicated that both chlorine and peracetic acid can reduce but not eliminate Salmonella on papaya, and sponge or microfiber mediated cross-contamination can occur at low frequency. The risk of this cross-contamination can be effectively managed by frequent dipping sponge or microfiber in sanitized solutions. Data generated from this study can be used to support and improve the food safety guidelines for papaya production.

Technical Abstract: Imported papayas from Mexico have been implicated in several salmonellosis outbreaks in the United States in recent years. While postharvest washing is a critical process to remove latex, dirt, and microbes, it also has the potential of causing cross-contamination by foodborne pathogens, with sponge or other fibrous rubbing tools often questioned as potential harboring or transmitting risk. In this study, Salmonella inactivation and cross-contamination via sponges and microfiber wash mitts during simulated papaya washing and cleaning were investigated. Seven washing treatments (wash without sanitizer; wash at free chlorine 25, 50, and 100 mg/L, and at peracetic acid 20, 40, and 80 mg/L), along with unwashed control, were evaluated, using Salmonella strains with different antibiotic markers differentially inoculated on papaya rind and on wash sponge or microfiber mitts. Salmonella survival and transfer on papaya and on sponge/microfiber, and in wash water were detected by plate count and selective enrichment. The washing and cleaning process reduced Salmonella on inoculated papayas by 1.69-2.66 and 0.69-1.74 log for sponge and microfiber cleaning, respectively, with the reduction poorly correlated to sanitizer concentration. Salmonella on inoculated sponge or microfiber was under detection limit (1 log CFU/cm2) by plate count, but remained recoverable by selective enrichment. Transference of Salmonella from inoculated papaya to sponge/microfiber, and vice versa, could be detected sporadically by selective enrichment, especially when washing was conducted in lower concentration of either sanitizer. Sponge/microfiber mediated Salmonella cross-contamination from inoculated to uninoculated papayas was frequently detectable by selective enrichment when washing was conducted in water with low concentration of either sanitizer, but rendered undetectable by dipping sponge/microfiber in sanitizing wash water between washing different papaya fruits. Therefore, maintaining adequate sanitizer levels and frequently dipping sponge/microfiber in sanitizing wash water can effectively mitigate risks of Salmonella cross-contamination associated with postharvest washing, especially with regard to the use of sponge or microfiber wash mitts.