piperidines and trigonelline

N,N-dimethylpiperidinium (mepiquat) is a new process-induced compound formed from natural constituents during the cooking process. Mepiquat was first found in coffee and cereal products, but its formation mechanism in coffee is still unclear. In the current study, Arabica and Robusta coffee beans were roasted at different temperatures (215, 220, and 230 °C) to study the effect of roasting process on mepiquat formation. The highest mepiquat content, 1,020 µg/kg, was found in dark roast (230 °C) Indonesia Wahana, while 430 µg/kg of mepiquat was detected in medium roast (220 °C) Vietnam Robusta. At the same roasting temperature, higher level of mepiquat was observed in Arabica than in Robusta. In both species, substances related to mepiquat formation, including betaine, choline, trigonelline, lysine, carnitine, pipecolic acid (PipAc), pipecolic acid betaine (PipBet), were also detected. The lysine-based Maillard reaction and decarboxylation in Arabica and Robusta promoted mepiquat formation through the degradation of choline and trigonelline, and the formation of intermediate products. Results from both the model system and selected commercial beans showed that choline and trigonelline had a significant correlation (P < 0.01) with mepiquat formation in Arabica. PRACTICAL APPLICATION: Mepiquat is considered as a new process-induced compound resulting from typical roasting conditions, but its formation mechanism in coffee is still unclear. This work demonstrates the formation mechanism of mepiquat by many precursor substances contained in Arabica and Robusta. It is very important to figure out how mepiquat is ''naturally" present in daily diets, especially in those processed at high temperatures.

Topics: Alkaloids; Coffea; Coffee; Cooking; Hot Temperature; Indonesia; Maillard Reaction; Pipecolic Acids; Piperidines; Seeds

This preliminary study reports for the first time the formation of N,N-dimethylpiperidinium (also termed mepiquat, a plant growth regulator used widely on cereal crops) by Maillard-driven degradation of lysine under dry thermal conditions and in the presence of the naturally occurring alkaloid trigonelline. The heat treatment was carried out at 240°C, and the resulting samples were analysed by liquid chromatography coupled to a high-resolution mass spectrometer (LC-HRMS) operating based upon Orbitrap technology. Results confirmed that lysine undergoes cyclisation by decarboxylative deamination in the presence of a carbonyl source (e.g. reducing sugars) to yield piperidine. Moreover, methyl rearrangement in the presence of trigonelline and under typical temperatures of roasting generates detectable amounts of mepiquat, identified by detailed mass fragmentation studies. The essential role of lysine in the formation of mepiquat was confirmed in a model system using (13)C₆-lysine, which showed the expected incorporation of five (13)C atoms into the mepiquat nitrogen heterocycle. These findings are relevant to the potential occurrence of mepiquat in roasted products such as coffee and cereals.

Topics: Alkaloids; Food Analysis; Hot Temperature; Lysine; Piperidines; Plant Growth Regulators

This study is the first to examine the role of choline and glycine betaine, naturally present in some foods, in particular in cereal grains, to generate N,N-dimethylpiperidinium (mepiquat) under Maillard conditions via transmethylation reactions involving the nucleophile piperidine. The formation of mepiquat and its intermediates piperidine - formed by cyclisation of free lysine in the presence of reducing sugars - and N-methylpiperidine were monitored over time (240°C, up to 180 min) using high-resolution mass spectrometry in a model system comprised of a ternary mixture of lysine/fructose/alkylating agent (choline or betaine). The reaction yield was compared with data recently determined for trigonelline, a known methylation agent present naturally in coffee beans. The role of choline and glycine betaine in nucleophilic displacement reactions was further supported by experiments carried out with stable isotope-labelled precursors (¹³C- and deuterium-labelled). The results unequivocally demonstrated that the piperidine ring of mepiquat originates from the carbon chain of lysine, and that either choline or glycine betaine furnishes the N-methyl groups. The kinetics of formation of the corresponding demethylated products of both choline and glycine betaine, N,N-demethyl-2-aminoethanol and N,N-dimethylglycine, respectively, were also determined using high-resolution mass spectrometry.

Topics: Alkaloids; Betaine; Carbon Radioisotopes; Choline; Chromatography, High Pressure Liquid; Deuterium; Hot Temperature; Kinetics; Lysine; Maillard Reaction; Methylation; Models, Chemical; Molecular Structure; Molecular Weight; Piperidines; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry