a Nestlé Research Centre , Lausanne 26 , Switzerland.
Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2014;31(12):1949-58. doi: 10.1080/19440049.2014.979371. Epub 2014 Nov 17.
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.
这项研究首次考察了胆碱和甜菜碱的作用，它们天然存在于一些食物中，特别是在谷物中，通过涉及亲核试剂哌啶的转甲基反应，在美拉德条件下生成 N,N-二甲基哌啶鎓（矮壮素）。在模型体系中，使用高分辨率质谱法监测了在 240°C 下长达 180 分钟的时间内（赖氨酸/果糖/烷基化剂（胆碱或甜菜碱）的三元混合物），美皮定及其中间体哌啶（在还原糖存在下通过游离赖氨酸的环化形成）和 N-甲基哌啶的形成情况。通过与最近在咖啡豆中天然存在的已知甲基化剂瓜氨酸的数据进行比较，评估了反应产率。通过使用稳定同位素标记的前体（¹³C 和氘标记）进行的实验，进一步证实了胆碱和甜菜碱在亲核取代反应中的作用。结果明确表明，美皮定的哌啶环来自赖氨酸的碳链，并且胆碱或甜菜碱分别提供 N-甲基基团。还使用高分辨率质谱法确定了胆碱和甜菜碱相应脱甲基产物，即 N,N-二甲基-2-氨基乙醇和 N,N-二甲基甘氨酸的形成动力学。
