Development of antibrowning and antimicrobial formulations to minimize listeria monocytogenes contamination and inhibit browning of fresh-cut "Granny Smith" apples

Authors: Fan, Xuetong; Sokorai, Kimberly; PHILLIPS, JOHN - Former ARS Employee

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2018
Publication Date: 4/26/2018
Citation: Fan, X., Sokorai, K.J., Phillips, J. 2018. Development of antibrowning and antimicrobial formulations to minimize listeria monocytogenes contamination and inhibit browning of fresh-cut "Granny Smith" apples. Postharvest Biology and Technology. 143:43-49.

Interpretive Summary: In recent years, there have been a number of recalls of cut apples due to contamination with Listeria monocytogenes, a pathogen capable of proliferation at low temperatures. Therefore, there is a need in the development of antimicrobial formulations to minimize the risk of Listeria contamination while maintaining the freshness of cut apples. In this study, organic acids and antioxidants were systematically evaluated to develop novel anti-listerial and anti-browning formulations. Results showed that formulations comprised of citric acid (a fruit acid), ascorbic acid (vitamin C) and N-acetyl-L-cysteine (an amino acid) were able to reduce populations of L. monocytogenes by more than 99.999% and at the same time, inhibited the surface browning of cut apples for least 21 days. The combinations can be applied by the fresh produce industry to enhance microbial safety and quality of apple slices.

Technical Abstract: In recent years, there have been a number of Listeria monocytogenes recalls involving fresh-cut apples, probably contaminated during treatments 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 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 L. monocytogenes cells in the solutions prepared from the combinations was evaluated, and the changes in quality [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 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.