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

Amino acids as methyl donors for the formation of N,N-dimethylpiperidinium (mepiquat) in model systems and cooked mushrooms

In the present study, new methylating agents for the formation of N,N-dimethylpiperidinium (mepiquat) were evaluated in both model and mushroom systems. Mepiquat levels were monitored using five model systems; alanine (Ala)/pipecolic acid (PipAc), methionine (Met)/PipAc, valine (Val)/PipAc, leucine (Leu)/PipAc, and isoleucine (Ile)/PipAc. The highest level of mepiquat was 1.97% at 260 °C for 60 min (Met/PipAc model system). Piperidine can actively combine with methyl groups in thermal reactions to form N-methylpiperidine and mepiquat. Additionally, mushrooms rich in amino acids were oven baked, pan cooked, and deep fried, respectively, to investigate the formation of mepiquat. Oven baking led to the highest mepiquat content of 63.22 ± 0.88 μg/kg. In summary, food constituents are the main source of precursors for mepiquat formation, the mechanism of which has been presented in both model systems and mushroom matrices rich in amino acids.

Untargeted Metabolite Profiling of Adipose Tissue in Rats Exposed to Mepiquat

Mepiquat (Mep) is a contaminant produced by Maillard reaction with reducing sugar, free lysine and an alkylating agent under typical roasting conditions, particularly in the range of 200-240 °C. It has been reported that exposure to Mep is harmful to rats. However, its metabolic mechanism is still not clear. In this study, untargeted metabolomics was used to reveal the effect of Mep on the metabolic profile of adipose tissue in Sprague-Dawley rats. Twenty-six differential metabolites were screened out. Eight major perturbed metabolic pathways were found, which were linoleic acid metabolism, Phenylalanine, tyrosine, and tryptophan biosynthesis, phenylalanine metabolism, arachidonic acid metabolism, Glycine, serine, and threonine metabolism, glycerolipid metabolism, Alanine, aspartate, and glutamate metabolism, and glyoxylate and dicarboxylic acid metabolism. This study lays a solid foundation for clarifying the toxic mechanism of Mep.

Effects of thermal processing on N,N-dimethylpiperidinium (mepiquat) formation in meat and vegetable products

N,N-dimethylpiperidinium (mepiquat) is an important food contaminant formed from natural ingredients during thermal processing. In this study, mepiquat formation in meat (pork and beef) and vegetables (potatoes and broccoli) was investigated via HPLC-MS/MS; the investigated cooking methods were oven baking, pan cooking, deep frying, and microwaving. The results showed that, among all foods, oven-baked potatoes showed the highest mepiquat level of 1064 μg/kg, which appeared after 20 min at 240 °C. The residual rates of mepiquat precursors, pipecolic acid (PipAc), betaine, choline, and trigonelline, were determined in oven-baked potatoes to investigate their correlation with mepiquat formation. The PipAc levels reduced by 99.8% at 260 °C after 30 min of oven baking, exhibiting a significantly high decomposition rate. Therefore, PipAc could be used as a marker of quality for the detection of mepiquat in thermally processed foodstuffs.

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

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.

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

BACKGROUND

The use of exo-16,17-dihydro-gibberellin A5-13-acetate (DHGA₅ ) in agriculture has been limited by its low synthetic yield. This study was aimed at optimizing the synthetic route of DHGA₅ , designing and synthesizing new derivatives with strong plant growth inhibitory activities.

RESULTS

Previous synthetic methods were replaced with a shorter, milder and faster reaction route with higher yield (76.3%) of DHGA₅ . Based on this novel route, a series of new derivatives were designed and synthesized using DHGA₅ as a lead compound and characterized and evaluated for biological activities in Arabidopsis thaliana. Among the 15 tested derivatives, compound 14j showed a lower medium inhibition concentration (IC₅₀ , 73 μm) in Arabidopsis than that of DHGA₅ (91 μm). Gibberellin deficient mutant assay further revealed that 14j had very different activities compared to DHGA₅ as it specifically inhibits gibberellin biosynthetic pathways. In addition, 14j does not influence the interaction between gibberellin receptors (GID1) and the master growth repressor (RGA) based on yeast two-hybrid assay.

CONCLUSION

The optimized synthetic route provides a promising method for large-scale preparation of DHGA₅ . Our biological assays indicate that 14j likely acts on gibberellin signaling elements other than GID1. These results indicate that novel plant growth regulators can be developed. © 2019 Society of Chemical Industry.