Reactions of citrinin with amino compounds modelling thermal food processing

Abstract

Citrinin (CIT) is a nephrotoxic mycotoxin, produced by several species of Penicillium, Aspergillus, and Monascus. The foodstuffs most frequently contaminated with CIT include cereals, cereal products, and red yeast rice. Studies on the occurrence of CIT in food have shown that the CIT concentrations in processed cereal-based products are generally lower than in unprocessed industry cereal samples. One possible explanation is the reaction of CIT with major food components such as carbohydrates or proteins to form modified CIT. Such modified forms of CIT are then hidden from conventional analyses, but it is possible that they are converted back into the parent mycotoxin during digestion. The aim of this study is therefore to investigate reactions of CIT with food matrix during thermal processes and to gain a deeper understanding of the degradation of CIT during food processing. In this study, we could demonstrate that CIT reacts with amino compounds such as proteins, under typical food processing conditions, leading to modified forms of CIT.

Keywords: Biomonitoring; Citrinin; Degradation; Food; Mycotoxin; Stability.

Fig. 1

Chemical structure of CIT in its tautomeric forms p-quinone and o-quinone, as well as the chemical structure of the ¹³C₃-labeled CIT

Fig. 2

Combined extracted ion chromatogram of an UHPLC-QTOF analysis of CIT (a) heated for 10 min at 160 °C with water addition. Several degradation products were observed. Identified products: DCIT (b). Tentatively identified products: phenol A acid (c), dicitrinin A (d), dicitrinin C (e), and citrinin H1 (f). Structurally unknown degradation products with m/z 395.1856 ([M + H]⁺, C₂₄H₂₆O₅) (g) and m/z 425.1960 ([M + H].⁺, C₂₅H₂₈O₆) (h)

Fig. 3

Thermal stability of CIT during heating with and without the matrix model compound (N_α-acetyl-L-lysine-methyl ester) for different times (10, 30, 60 min) and temperatures (100, 120, 140, 160, 180 °C). The standard deviation, is given for analysis of pure CIT samples in triplicate, the mean deviation for analysis of CIT and model compound in duplicate, indicated by error bars

Fig. 4

HRMS product ion spectrum of the reaction product of CIT and lisinopril with m/z 638.3082, retention time: 6.8 min, 44.1 eV ([M + H]⁺, C₃₄H₄₃N₃O₉). The postulated structure is given in the right corner of the fragment spectrum. Fragmentation pathways can be recognized by the arrows

Fig. 5

Volcano plot of the univariate data analysis of the heating experiment of CIT with gluten: on the right side features of the test group (CIT + gluten) and on the left side features of the control group (¹³C₃-labeled CIT + gluten) are shown

Fig. 6

HRMS product ion spectrum of the feature with m/z 324.1456, retention time: 4.4 min, 30.6 eV ([M + H]⁺, C₁₆H₂₁NO₆). The feature, that is presumably a thermal reaction product of CIT and an amino acid, is formed in the heating experiment of CIT with gluten (samples were digested with pronase E after heating). Typical CIT fragments are highlighted in red boxes, typical CIT fragmentation pathways like the loss of two water molecules and the loss of carbon monoxide can be recognized by the arrows