Electrostatic spraying of organic acids on biofilms formed by E. coli O157:H7 and Salmonella Typhimurium on fresh produce

Abstract

Electrostatic spraying which has an even and retained surface coverage could be an effective novel technique to completely cover the surface of fresh produce to disrupt biofilm formation by pathogenic bacteria. Spinach leaves and cantaloupe rind were spot-inoculated with a bacterial culture and stored at 8°C for 72h to allow biofilm formation. Among various green fluorescent protein-labeled strains, ED 14 strain of E. coli O157:H7 and SD 10strain of Salmonella Typhimurium had the best attachment based on colony counts. The produce samples were electrostatically sprayed with malic (MA) and lactic (LA) acid solutions alone (1.0/2.0/3.0/4.0% w/v) or in combination (0.5+0.5/1.0+1.0/1.5+1.5/2.0+2.0% w/v) to test for a reduction in the attached bacteria. A combined treatment of LA 2.0% w/v+MA 2.0% w/v had the highest log reduction (CFU/disk) of 4.14 and 3.6 on the attached E. coli strain ED 14 (spinach) and Salmonella strain SD 10 (cantaloupe), respectively. Crystal violet assay demonstrated the disruptive effect of organic acids on biofilms formed by the pathogenic bacteria. Application of electrostatic spray with a combination of malic and lactic acids resulting in a log reduction (CFU/disk) of 3.6 or higher can improve the microbial safety of spinach and cantaloupe by preventing the pathogenic biofilm formation and bacterial growth.