Carnitine, A New Precursor in the Formation of the Plant Growth Regulator Mepiquat

Abstract

Carnitine is demonstrated as an effective methyl donor in the formation of the plant growth regulator N, N-dimethylpiperidinium (mepiquat), encompassing either N-methylation/decarboxylation of pipecolic acid, or Maillard pathways followed by transmethylation reactions. The formation of mepiquat and the intermediate compounds was monitored (180-300 °C, up to 180 min) using HPLC-MS/MS in different binary or ternary model systems composed of (i) lysine/fructose/carnitine, (ii) lysine/glucose/carnitine, or (iii) pipecolic acid (PipAc)/carnitine. The highest yield of mepiquat was 2.4% after 120 min incubation at 290 °C (PipAc/carnitine model system). The highest yield was recorded in fructose and glucose (Maillard) systems after 180 min at 230 °C. The full-scan mode was used to monitor the formation of the corresponding intermediates (piperidine and N-methylpiperidine, the demethylated intermediates of carnitine). The new pathways of mepiquat formation indicate that the occurrence of low levels of this thermally induced compound is potentially more widespread in some selected cooked foodstuffs. For the first time, mepiquat was detected in oven-cooked beef, reaching up to 82.5 μg/kg. These amounts are not expected to significantly contribute to the overall exposure via different foodstuffs, as reported in previous studies.

Heat‐induced formation of N,N‐dimethylpiperidinium (mepiquat) in Arabica and Robusta coffee

“…The six‐point calibration curve for lysine and PipAc was prepared with a range of 0 to 100 µg/mL. The mepiquat concentrations were 0, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.5, 1 µg/mL, and 0.02 µg/mL d 3 ‐mepiquat was used as an internal standard according to our previous study (Yuan et al., 2018). All solutions were stored at −20 °C for up to 2 weeks before use.…”

“…Mepiquat (or its chloride salt) is not registered for use on coffee and should not be detected in green coffee beans. The MRL of mepiquat in the European Union is at 0.1 mg/kg and the toxicity of mepiquat has become a potential factor affecting food safety (Wermann et al., 2014; Yuan et al., 2018). Mepiquat has recently received attention as a process‐induced compound resulting from typical roasting conditions.…”

“…Mepiquat has recently received attention as a process‐induced compound resulting from typical roasting conditions. Recent studies have demonstrated that mepiquat was formed under decarboxylation and the Maillard reaction conditions at high temperatures in the model system (Yuan et al., 2018; Yuan, Tarres, Bessaire, Stadler, & Delatour, 2017). N ‐methylpiperidine is an important intermediate involved in the formation of mepiquat (Bessaire, Tarres, Delatour, & Stadler, 2014; Hammel, Dubois, Delatour, & Stadler, 2014).…”

“…In essence, mepiquat arises from the Maillard‐type reaction that requires free lysine, a reducing sugar, and an alkylating agent, heated under dry conditions (Bessaire et al., 2014; Hammel et al., 2014; Stadler et al., 2003). The alkylating agents associated with mepiquat formation include betaine, choline and trigonelline, and carnitine (Yuan et al., 2018). Pipecolic acid (PipAc) or pipecolic acid betaine (PipBet) also plays an important role in the formation of mepiquat.…”

Improved synthetic route of exo‐16,17‐dihydro‐gibberellin A5‐13‐acetate and the bioactivity of its derivatives towards Arabidopsis thaliana

“…There are many commercially available synthetic products with plant growth retardant properties such as paclobutrazol, mepiquat chloride and prohexadione‐Ca (Fig. (a)) . Although these chemicals are fast‐acting and potent, they have obvious disadvantages, including poor environmental degradation and especially adverse effects on the flowering of plants and ripening of fruits .…”