Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2003
Publication Date: 1/15/2004
Citation: Karaibrahimoglu, Y., Fan, X., Sapers, G.M., Sokorai, K.J. 2004. Effect of ph on the survival of listeria innocua in calcium ascorbate solutions and on quality of fresh-cut apples. Journal of Food Protection. 67:751-757.
Interpretive Summary: Fresh-cut apples represent a rapidly growing segment of the fresh-cut produce industry. Cut apples must be treated with a processing aid solution to prevent development of an unsightly brown discoloration. Such solutions usually contain ascorbic acid (vitamin C) and may be acidic or neutral in pH; the latter category has received wide acceptance by the industry. However, under conditions of extended use, microorganisms including human pathogens, can survive and grow in the neutral ascorbate solutions. A product recall due to presence of the pathogen Listeria monocytogenes in fresh-cut apples was attributed to processing aid contamination. In this research, we investigated means of suppressing the growth of Listeria in neutral calcium ascorbate solutions. Reducing the solution pH from 7 to between 4.5 and 5 by addition of acetic acid (the acid in vinegar) was highly effective in killing Listeria innocua, a bacteria closely related to the human pathogen. This treatment had no effect on the stability of ascorbic acid or on the color or texture of the cut apples, but greater pH reduction had detrimental effects. Commercial use of a pH-reduced calcium ascorbate solution should decrease the potential risk of foodborne illness due to consumption of products prepared with contaminated ascorbate solutions.
Technical Abstract: Fresh cut apple slices were dipped in calcium ascorbate (CaA) solution at pH values ranging from 2.5 to 7.0 to inhibit browning. After treatment, the cut apples were stored at 4 and 10 degree C for up to 21 days. Color and texture of the apples were determined on Days 1, 14 and 21. In a separate experiment, the pH of CaA solution was adjusted with acetic acid to 6 different pH levels between 2.5 and 7.0, and the solution was inoculated with Listeria innocua. The survival of the bacterium and the stability of CaA were determined at 0, 20 and 96 h. The cut apples maintained fresh quality when the pH of the CaA solution was above 4.5, but slight discoloration of apple slices dipped in pH 4.5 solution was observed after 14 days at 10°C. At pH 5.0, the CaA dip maintained the quality of the apples at both temperatures for at least 21 days. The Listeria population was reduced by 4-5 log10 cfu/mL at pH 4.5 after 96 h. At pH 5, the bacterial population in the CaA solution was reduced by ~2 log cfu/mL during the same time period. The CaA solution was stable at pH 5 for at least 96 h. Reduction of the pH to between 4.5 and 5.0 should greatly reduce the risk of foodborne illness due to consumption of fresh-cut apples treated with a CaA solution contaminated with Listeria.