Development of antibrowning and antimicrobial formulations to minimize Listeria monocytogenes contamination and inhibit browning of fresh-cut “Granny Smith” apples

In recent years, there have been a number of Listeria monocytogenes recalls involving fresh-cut apples treated with antibrowning solutions. In the present study, we used response surface methodology to develop and optimize formulations for reducing L. monocytogenes populations in the solutions and for maintaining cutting surface color of apple slices. The following two sets of three chemicals at various levels were combined: citric acid + calcium ascorbate+ N-acetyl-l-cysteine (NAC), and citric acid + ascorbic acid +NAC. The survival of a 4-strain cocktail of L. monocytogenes cells (F2365, serotype: 4b; NRRL 33857, serotype: 1/2a; NRRL 33723, serotype: 1/2a; NRRL 33230, serotype: 4c) in the solutions prepared from the combinations was evaluated, and the changes in cutting surface color parameters (L*, a* and b*) and skin edge browning of “Granny Smith” apple slices dipped in the solutions for 3 min were assessed during 21 d of storage at 4 °C. Results showed that combinations of citric acid, calcium ascorbate and NAC were ineffective in achieving 5 log reduction of L. monocytogenes. However, formulations comprised of 4.0-4.5 % citric acid, 3-4% ascorbic acid and 1.5-2.0% NAC achieved more than 5 log reduction of L. monocytogenes in the solutions, and the cutting surface of apple slices treated with these formulations maintained L* values of > 70, and a* values of < −1.8 during 21 d of storage. Our results suggest that the combinations of citric acid, ascorbate and NAC may be used to enhance microbial safety of fresh-cut apples without compromising product quality.