Elucidation of the mechanism of formation of thermally generated volatile and non-volatile Maillard reaction products using isotope labeling technique combined with ESI-TOF MS/MS and GC/MS analysis.

糖和氨基酸是热加工食品产生独特香气和颜色的关键成分。许多味道不好的生食可以通过糖和氨基酸的相互作用（称为美拉德反应），通过面包烘焙、咖啡烘焙和巧克力制造等过程转化为理想的产品。在生理条件下，许多机体蛋白质也可以通过类似的与糖的相互作用进行修饰，特别是在糖尿病患者中，可能导致生理和免疫功能的损害。不幸的是，同样的化学相互作用也会导致烹饪过程中产生食物毒物，如杂环胺、丙烯酰胺、呋喃和糖毒素。了解上述许多关键食物成分形成的机制有助于我们控制它们的产生。寻找最佳条件来降低不同毒物的含量，同时保留美拉德衍生的香气化合物，从而提高食品的质量和安全性，是当今食品工业面临的主要挑战之一。申请人的长期目标是研究通过使用模型系统形成的挥发性和非挥发性化合物的来源和形成机制。申请人开发了一种简便的方法，通过与特定标记的糖（13C-1, 13C-2，…13C-6）和氨基酸（15N, 13C-1, 13C-2等）进行反应，将13C-和15N标记的原子引入到反应产物中，将热解- gc /MS作为综合反应，分离和鉴定系统。热解在100-250℃之间进行20秒，只需要亚毫克量的昂贵的标记前体，从而大大降低了进行此类实验所需的成本和时间。在250°C下热解20秒可以模拟在110°C下加热1小时。使用标记反应物的优点之一是，反应产物的所有C和n原子都可以追溯到它们在起始物质中的来源。这可以阐明它们的形成机制和质谱片段的结构分配。使用上述方法，申请人能够阐明与食品有关的各种热生成挥发性和半挥发性化合物（如丙烯酰胺、呋喃、吡嗪等）的形成机制。然而，热解后残留的极性残留物也以标记极性产物的形式含有相当数量的化学信息。申请人的短期目标是(1)除挥发物外，在选定的模型系统中分析这些残留物的非挥发性成分。分析相同样品的挥发物及其残留物的非挥发物的策略允许在两个馏分中识别化合物的标记结合模式，而无需使用昂贵的标记前体进行额外的实验，并将两种途径机械地联系起来。由于最近发现加热食品（油炸、烧烤等）的食用水平与与衰老相关的慢性疾病之间存在联系，因此非挥发性残留物可以成为有关颜色、味道和毒性来源的丰富信息来源。(2)研究选定的食品基质组分如酚类、盐类等对美拉德反应方向的影响。这些参数尚未被系统地研究过。

Sugars and amino acids are the key components responsible for the generation of distinctive aroma and color of food products subjected to thermal processing. Many unpleasant-tasting raw foods can be transformed by the interaction of sugars and amino acids (known as Maillard reaction) into desirable products via processes such as bread baking, coffee roasting and chocolate manufacture. Under physiological conditions, many body proteins also can be modified through similar interaction with sugars, specially, in diabetic patients that may result in the impairment of physiological and immunological functions. Unfortunately, this same chemical interaction is also responsible for the thermal generation of food toxicants during cooking such as heterocyclic amines, acrylamide, furan and glycotoxins. Understanding the mechanism by which many of the above mentioned critical food components are formed can contribute to our ability to control their generation. Finding optimal conditions to lower the levels of different toxicants and at the same time retain the Maillard-derived aroma compounds and hence improve the quality and safety of foods, is one of the main challenges of the food industry today. The long term objective of the applicant is to study the origin and the mechanism of formation of volatile and non-volatile compounds formed through the use of model systems. The applicant has developed a convenient method of introducing 13C- and 15N-labeled atoms into the reaction products, through carrying out the reactions with specifically labeled sugars (13C-1, 13C-2, …13C-6) and amino acids (15N, 13C-1, 13C-2 etc) using Pyrolysis-GC/MS as an integrated reaction, separation and identification system. The pyrolysis is conducted between 100-250oC for 20 seconds and requires only sub-milligram quantities of the expensive labeled precursors, thus reducing drastically the cost and time needed to carry out such experiments. Pyrolysis at 250°C for 20 seconds has been shown to mimic heating at 110oC for 1h. One of the advantages of using labeled reactants is that all the C- and N-atoms of a reaction product can be traced back to their origin in the starting material. This can permit elucidation of the mechanism of their formation and structural assignment of their mass spectral fragments. Using the above approach the applicant was able to elucidate the mechanism of formation of various thermally generated volatile and semi-volatile compounds relevant to food such as acrylamide, furan, pyrazines, etc. However, the polar residue remaining after the pyrolysis also contains considerable amount of chemical information in the form of labeled polar products. The short term objectives of the applicant is (1) to analyze these residues in selected model systems for their non-volatile components in addition to the volatiles. The strategy of analyzing the same sample for the volatiles and its residue for non-volatiles allows identification of label incorporation patterns of compounds in both fractions without having to perform additional experiments with costly labeled precursors and to mechanistically link the two pathways. The non-volatile residue can be a rich source of information regarding the origin of color, taste and toxicity due to recently identified link between the levels of consumption of heated foods (fried, grilled, etc.) and chronic diseases associated with aging. (2) To study the influence of selected food matrix components such as phenolics, salts etc on the direction of the Maillard reaction. These parameters have not been studied systematically.