Efficacy of Acetic Acid against Listeria monocytogenes Attached to Poultry Skin during Refrigerated Storage

Abstract: This work evaluates the effect of acetic acid dipping on the growth of Lmonocytogenes on poultry legs stored at 4 °C for eight days. Fresh inoculated chicken legs were dipped into either a 1% or 2% acetic acid solution (v/v) or distilled water (control). Changes in mesophiles, psychrotrophs, Enterobacteriaceae counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated. The shelf life of the samples washed with acetic acid was extended by at least two days over the control samples washed with distilled water. L.monocytogenes counts before decontamination were 5.57 log UFC/g, and after treatment with 2% acetic acid (Day 0), Lmonocytogenes counts were 4.47 log UFC/g. Legs washed with 2% acetic acid showed a significant (p < 0.05) inhibitory effect on Lmonocytogenes compared to control legs, with a decrease of about 1.31 log units after eight days of storage. Sensory quality was not adversely affected by acetic acid. This study demonstrates that while acetic acid did reduce populations of L. monocytogenes on meat, it did not completely inactivate the pathogen. The application of acetic acid may be used as an additional hurdle contributing to extend the shelf life of raw poultry and reducing populations of L.monocytogenes.

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Alex’s Notes: Normally I wouldn’t be interested in this type of study, but the words “acetic acid” in the title caught my attention given our recent discussion on the benefits of vinegar. As we know, food vinegar is 5-6% acetic acid. The researchers of the current study bough 90 fresh chicken legs and infected them with Listeria pathogens. They were then divided in three groups, each containing 30 legs: dipped for five minutes into sterile distilled water (control), 1% acetic acid solution (group 2), or 2% acetic acid solution (group 3).

Compared to the control legs, the acetic acid groups consistently inhibited the growth of all tested pathogens and food spoilage bacteria (mesophiles, psychrotophs, enterobacteriaceae, & Listeria monocytogenes) with the 2% solution outperforming the 1% solution. The initial effects were so pronounced that the acetic acid halted all growth for the first day so that days 0 & 1 of testing had the same microbial counts (technically called “extending the lag phase”).

In addition to the inhibition of bacteria, and likely a side-effect of it, the acetic acid groups had a shelf-life of eight days compared to six for the control group. By this the researchers mean that the acetic acid groups didn’t discolor or have off-odors, and the acetic acid didn’t affect the quality characteristics of the legs either. All this is likely due to the acidity of the legs, which was stable just above pH 4 for the 2% acetic acid group, pH 5 for the 1% acetic acid group, and pH 6 for the controls.

So what does all this mean? It likely means that creating an acidic environment prolongs shelf-life and inhibits the growth of pathogens! These effects have also been demonstrated with pork and beef, and fermentation has been around for, well, ever. While it cannot be said for certain, this raises questions about the effectiveness for household vinegar which is 5-6% acetic acid. Given the effects were mediated by an acidic environment; it stands to reason that they would be more pronounced in a more concentrated solution. However, this may make the meat taste tangy or have some weird sensory characteristics. It also has me wonder about lemon juice. Regardless, there is definitely a place for this in food preparation, perhaps by rinsing the meat in vinegar before cooking or marinating it in lemon juice before storage.

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