Application of polylactic acid coating with antimicrobials in reduction of Escherichia coli O157:H7 and Salmonella stanley on apples

Authors: Jin, Zhonglin; Niemira, Brendan

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2010
Publication Date: 4/6/2011
Citation: Jin, Z.T., Niemira, B.A. 2011. Application of polylactic acid coating with antimicrobials in reduction of Escherichia coli O157:H7 and Salmonella stanley on apples. Journal of Food Science. 76(3):184-188.

Interpretive Summary: The number of documented foodborne outbreaks associated with consumption of raw fruits and vegetables has increased in recent years. Some outbreaks of illnesses have been linked to the consumption of fruit and vegetable products such as unpasteurized apple cider contaminated with E. coli O157:H7, fresh-cut melon contaminated with Salmonella and ready-to-eat spinach. Apples could be contaminated by foodborne pathogens in the field or during postharvest handling through bird droppings, fruit flies, faecal contamination, water, equipment or infected handlers. Water washing and aqueous sanitization of whole apples have not been successful in significantly reducing E. coli O157:H7, Listeria monocytogenes, or Salmonella on apples. Therefore, a new effective intervention technology is needed. In this study, an antimicrobial coating method was developed to decontaminate apples. Golden Delicious apples were inoculated with Escherichia coli O157:H7 or Salmonella Stanley and coated with polylactic acid polymer containing lactic acid (LA), disodium ethylenediaminetetraacetic acid (EDTA), sodium benzoate (SB), potassium sorbate (PS), or their combination (LA+EDTA, SB+LA, SB+LA+EDTA). Survival of Escherichia coli O157:H7 and Salmonella Stanley on apples during 14 days’ storage at 4 degree C were investigated. The data show that antimicrobial coatings reduced populations of E. coli O157:H7 and S. Stanley by up to 99.99% at 1 day and 99.995% at 14 days. The antimicrobial PLA coating provides an alternative intervention to reduce the pathogens on apples.

Technical Abstract: Survival of Escherichia coli O157:H7 and Salmonella Stanley on apples as affected by application of an antimicrobial polylactic acid (PLA) coating were investigated. Golden Delicious apples were spot inoculated with E. coli O157:H7 or S. Stanley and spray coated with PLA/solvent solutions containing lactic acid (LA), disodium ethylenediaminetetraacetic acid (EDTA), sodium benzoate (SB), potassium sorbate (PS), or their combination (LA+EDTA, SB+LA, SB+LA+EDTA). Apples without any coating treatment served as controls. Coating treatments were allowed to dry fully and the apples were stored at 4 degree C for 14 days. Antimicrobial coatings reduced populations of E. coli O157:H7 and S. Stanley by up to 4 log CFU per square centimeter at 1 day and 4.7 log CFU per square centimeter at 14 days, compared to controls. SB+LA combination had a similar effectiveness as the SB+LA+EDTA combination against both pathogens and was more effective than other coating treatments. Without antimicrobial treatment, E. coli O157:H7 and S. Stanley were able to survive on apples stored at 4 degree C for up to 14 days. The antimicrobial PLA coating provides an alternative intervention to reduce the pathogens on apples.