Salmonella: catch me if you Cayenne!

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  • Published: Dec 13, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: Salmonella: catch me if you Cayenne!

Beastly business

Microbial beasts use evil trickery to establish themselves on supermarket shelves. However, they have been met by the wrath of American scientists, who have crafted a speedy, selective method of HILIC-HPLC-MS for antimicrobial acid identification in foodstuffs. Image courtesy of 'Atilin'/Wikipedia (GNU Free Documentation License).

Salmonella: a notorious brute whose vehemence is yet to be settled. Regrettably, we bring news of a less commonly recognised host of Salmonella enterica serotypes—the chili pepper. Even dried peppers provide sufficient conditions to harbor the microbe, with slight exposure to moisture allowing for its growth and spread. With the adverse symptoms associated with this beast’s accrual, including diarrhea, dehydration and even death, we desire an effective culling mechanism for the persistent fiend.

The pepper species Capsicum annum has taken a stand, providing specific apparatus with which to combat the pest. It has not given the information up lightly, however. We must first correctly isolate the effective components from a complex labyrinth of bioagents. Capsaicins, organic acids and phenolic compounds have already been implicated as key inhibitors of bacterial growth, but a specific antimicrobial individual within these genres is yet to be confirmed in the Capsicum genus.

Gearing up

Previous efforts to overcome the problem by HPLC analysis have implicated specific Capsicum annum-derived organic acids as effective weapons, including trans-cinnamic and hydroxy-cinnamic acids. Unfortunately, the methods supporting this hypothesis were inappropriate, providing opportunity for compound misidentification by spectral overlap and interference.

A research team from the US Food and Drug Administration (US FDA) took it upon themselves to derive a more selective process of organic acid identification, allowing more accurate quantitation of cinnamic acids.

Plans to implement the hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) method for trans-cinnamic and hydroxy-cinnamic acid analysis were formulated. Jablonski, heading the team, told us how their developments involved, “electrospray ionization in negative mode with multiple reaction monitoring for detection.”

The Illinois-based researchers purchased 15 varieties of chili pepper, all within the Capsicum genus, from local markets. MRM transition values of standards (trans-cinnamic, 2-OH-cinnamic, 4-OH-cinnamic and 4-Cl-benzoic acids) were determined. This involved the use of an ammonium formate buffer (pH 6.0) in the mobile phase to enhance acid ionisation for negative ESI-MS detection. Using these values as references, the presence of trans-cinnamic and 4-OH-cinnamic acid was observed in every chili variety. 2-OH-cinnamic acid was not detected but, instead, they observed an unknown hydroxy-cinnamic acid derivative in all chilies.

Jablonski’s technique was not only intended to confirm organic acid presence. He also stated that he wished “to use this method to test the hypothesis that these compounds are a major cause of growth inhibition of Salmonella in Capsicum peppers”. Pepper samples containing predetermined cinnamic acid concentrations were inoculated with a cocktail of Salmonella enterica serotypes. No correlation was observed between salmonella growth and cinnamic acid content. The American scientists thereby reveal that the previously hypothesized antimicrobial properties of cinnamic acids are unlikely or, at least, not key.

Armory advancements

Selectivity enhancements by use of tandem MS, as well as the high sensitivity demonstrated by the capacity to measure an LOQ of as little as 0.01 ppm, highlight huge advances in the methods developed by Jablonski’s research group. Their use of 4-Cl-benzoic acid to spike peppers prior to extraction as an internal standard also eliminated requirements for isotopically labeled cinnamic acid analogs in food matrices. Further, HILIC-MS has made the analysis of polar substances such as trans-cinnamic acid feasible.

Research conducted by the team has provided a simple, selective and sensitive HILIC-MS method that allows for the separation and detection of polar acid compounds present in any food matrix. The group’s efforts are ongoing; they believe that “more research is needed to better understand the specific components/characteristics(s) of Capsicum peppers that limit growth of the bacterial pathogen Salmonella.”

Related Links

Journal of Food Biochemistry, 2016, 40, Early View paper. Jablonski et al. Hydrophilic interaction liquid chromatography-mass spectrometry for cinnamic acid determination and its use to evaluate components of dried hot peppers (Capsicum annum) associated with growth inhibition of Salmonella enterica serovars.

Wikipedia, Salmonella enterica

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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