Combined effects of malic acid dip and pulsed light treatments on the inactivation of Listeria innocua and Escherichia coli on fresh-cut produce

• Fresh-cut produce was treated with malic acid and exposed to intense light pulses.
• Microbial counts were reduced when treatments were individually applied.
• Synergistic effects were observed when both treatments were combined.
• Transmission Electron Microscopy revealed structural changes in bacterial cells.

The application of pulsed light (PL) in combination with malic acid (MA) dips was evaluated regarding the inactivation of Listeria innocua or Escherichia coli inoculated on different fresh-cut products (avocado, watermelon and mushrooms) through refrigerated storage. The inoculated substrates were exposed to individual PL (180–1100 nm, 12 J/cm2) and MA (2% w/v) treatments or to a combination of both. The effects on the bacterial cell structure were confirmed by Transmission Electron Microscopy (TEM). When treatments were individually applied, inactivation of L. innocua and E. coli ranged from 0.91 to 1.1 log CFU/g and from 1.92 to 2.97 log CFU/g, respectively. Nevertheless, a much greater bactericidal effect was observed when the treatments were sequentially applied, leading to more than 5 log reductions of L. innocua and E. coli populations. TEM analysis revealed structural changes with modification of cytoplasmic contents and alteration of cell membranes. The results of this study indicate that the combination of assayed treatments may be applied to effectively control L. innocua and E. coli on the surface of fresh-cut products for at least two weeks of storage.