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。

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.