Impact of pH on the Stability and the Cross-Reactivity of Ochratoxin A and Citrinin

Abstract

Mycotoxins are secondary metabolites produced by several fungi contaminating crops. In several countries, the maximum permitted levels of mycotoxins are found in foodstuffs and feedstuffs. The common strategy of mycotoxin analysis involves extraction, clean-up and quantification by chromatography. In this paper, we analyzed the reasons of underestimation of ochratoxin A (OTA) content in wine, and overestimation of OTA in wheat, depending on the pH of the clean-up step and the simultaneous presence of citrinin (CIT). We demonstrated that the increase of pH by adding polyethylene glycol (PEG) to wine led to an underestimation of OTA by conversion of OTA into open ring ochratoxin A OP-OA. In comparing three methods of extraction and clean-up for the determination of OTA and CIT in wheat—(i) an inter-laboratory validated method for OTA in cereals using immunoaffinity column clean-up (IAC) and extraction by acetonitrile/water; (ii) a validated method using IAC and extraction with 1% bicarbonate Na; and (iii) an in-house validated method based on acid liquid/liquid extraction—we observed an overestimation of OTA after immunoaffinity clean-up when CIT is also present in the sample, whereas an underestimation was observed when OTA was alone. Under neutral and alkaline conditions, CIT was partially recognized by OTA antibodies.

Development of an in vitro method for the prediction of mycotoxin binding on yeast-based products: case of aflatoxin B1, zearalenone and ochratoxin A

“…High quantity of YCW (50 mg/ml) even in buffer solution lowered significantly the pH, modifying the analytical performance leading to incorrect analytical findings and as consequence to a misclassification of binder ability. Such interference with analytical method of OTA has been previously observed (Bazin et al 2013). Yiannikouris et al 2013 excluded data obtained with pH 7 because ZEA eluted in two peaks instead of a single peak with the pH values of 3.0 and 5.0.…”

“…Protonation of OTA is changed in the pH course, as it has a pK a of 4.4 and 7.3. At pH 3.0, almost all OTA will be in the neutral (non-charged) form, while at pH 7.4 it will be present as a monoanion or a dianion, and at pH 8.4 most OTA will be in the dianion form (Santos et al 2011;Bazin et al 2013).…”

In vitro exposure of Penicillium mycotoxins with or without a modified yeast cell wall extract (mYCW) on bovine macrophages (BoMacs)

“…For example, OTA is soluble in polar organic solvents at an acidic and neutral pH, whereas it is less soluble at a high pH. This is probably due to the conformational changes of OTA at different pHs (Bazin et al 2013). Bazin et al (2013) also discussed that OTA at a high pH undergoes a conformational change, leading to formation of the open ring form of OTA, which affected binding to detection antibodies.…”

“…This is probably due to the conformational changes of OTA at different pHs (Bazin et al 2013). Bazin et al (2013) also discussed that OTA at a high pH undergoes a conformational change, leading to formation of the open ring form of OTA, which affected binding to detection antibodies. Therefore, in the present study, conformational changes of OTA at a pH greater than 5.0 could have also decreased the strength of hydrogen bonding and van der Waals force between OTA and mYCW in Milli-Q water during the incubation, which could have lowered binding capacity (Yiannikouris et al 2004;El Khoury and Atoui 2010;Bazin et al 2013).…”

Electrochemical simulation of biotransformation reactions of citrinin and dihydroergocristine compared to UV irradiation and Fenton-like reaction

“…Similar electrochemical reaction products have already been described for the secondary fungi metabolites alternariol and alternariol methyl ether [19]. The fungi Penicillium citrinum decomposes CIT to dimethyl dicitrinin A [20], bearing two methoxy groups and demonstrates that the addition of a methoxy group achieved by EC is closely related to biochemical reactions in living systems. CIT-P 2 with m/z 225 resulted from the hydroxylation of CIT followed by the opening of the ring and the loss of carbon dioxide leading to the formation of citrinin H2.…”