ANALYSIS AND QUANTITATIVE DATA OF GLYCATION COMPOUNDS in Visual Studio .NET

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ANALYSIS AND QUANTITATIVE DATA OF GLYCATION COMPOUNDS
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In addition to the compounds mentioned here, several other reaction products of advanced stages of the Maillard reaction of proteins have been described, which to date have not been quanti ed unambiguously in foods, and therefore will not be discussed here. 2.7.3 ANALYSIS AND QUANTITATIVE DATA OF GLYCATION COMPOUNDS IN FOODS 2.7.3.1 Amino Acid Derivatives Despite the advances in modern instrumental analysis during the last decades, quanti cation of individual glycation compounds in food still remains an enormous challenge. For most of the compounds mentioned earlier, no standard material is commercially available. Establishing a strategy for analysis, therefore, rst of all requires synthesis of pure reference material of the said compound and suf cient characterization of the isolates in terms of identity and purity, based on spectroscopic characterization such as NMR and MS as well as elemental analysis. Next, quanti cation normally is only possible together with unambiguous identi cation, which means that the quantitative data generated by an analytical technique are only valid if they are supported by structural information. This is of special importance for methods that do not provide qualitative (structural) information together with the quantitative signal. Prominent examples, in this context, are immunological methods such as ELISAs (enzyme-linked immunosorbent assays), based on (more or less) speci c antibodies. If such methods were used for generating quantitative data, it normally would be an absolute must that the ELISA method used to quantify glycation compounds in certain matrices is validated by cross-checking the results with a more speci c method, like HPLC-MS. Especially for immunological methods, it is basic knowledge that the antigen antibody interaction is widely dependent on the milieu conditions and therefore on the composition of the matrix. An ELISA that works ne in urine may not give reliable results for cheese samples. Keeping this in the back of one s mind while screening the relevant literature, it may be obvious in many cases that data reported for glycation compounds do not ful ll the basic requirements for a credible analysis even if published in high-impact journals. It seems to be important to address this issue mainly because of recent publications reporting astonishing data of glycation compounds in foods (58). In the following, therefore, only these reports are mentioned in which valid data are reported based on the use of methods ful lling the aforementioned criteria. From the quantitative point of view, the early Maillard reaction, characterized by the formation of peptide-bound Amadori products, is the dominating modi cation found in foods (Table 2.7.1). It has been known since the early 1980s that heat treatment of milk, in particular sterilization, as well as longterm storage of milk or whey powder may lead to a signi cant lysine modi cation, reaching 10% to 20% in certain samples. Lactose-hydrolyzed whey may
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MAILLARD REACTION OF PROTEINS AND AGEs IN FOOD
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TABLE 2.7.1 Range of protein-bound Amadori compounds and AGEs in foods. Milk products Amadori Bakery products Pasta Coffee Roasted meat 1 10
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Up nd Bread crumb up to RM/PM: 1 2 to 200; bread crust UHT: 2 5 400 up to 800 SM: up to 50; cheese: up to 10; MP/WP: 50 to 200 (up to 700 in case of lactosehydrolyzed WP) CML nd 10 nd 20 Pyrraline nd 25 1 10, up to 180 in nd to case of bread crust 13 Pronyllysine Bread crumb: 0.01 Bread crust: 0.1 Pentosidine UHT: nd 0.01 nd 0.4 0.2 MG-H1 10 20, up to 700 in 100 350 case of alkalinetreated products
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Data are given as mmol/mol lysine or mmol/mol arginine (in the case of pentosidine and MG-H1). RM, raw milk; PM, pasteurized milk; UHT, UHT-treated milk; SM, sterilized milk; MP, milk powder; WP, whey powder; nd, not detected.
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even contain up to 70% modi ed lysine, which is due to the higher reactivity of monosaccharides compared with lactose (6). It is noteworthy that a lysine modi cation of 0.1% is found even in raw milk. This low amount of Amadori products is only slightly increased during pasteurization or UHT treatment. In bakery products, N- -maltuloselysine and N- -fructoselysine are the dominating lysine derivatives. Quanti cation of the extent of the early Maillard reaction can be achieved by measuring furosine, a reaction product that is formed from the Amadori products of lysine during acid hydrolysis (Fig. 2.7.5) (59, 60). For the use of furosine as well as corresponding furoylmethyl amino acids (FMAAs) as indirect parameters for Amadori products, it is necessary to have information on to which extent these derivatives are formed during acid hydrolysis (61). If the corresponding conversion factors are known, FMAAs quanti ed via ion-exchange chromatography (7), RP-HPLC with UV detection (62), or capillary electrophoresis (63), represent valuable analytical tools for sensitive monitoring of Amadori product formation not only in foods but also in biological samples such as blood or urine (64, 65). The group of Erbersdobler was the rst to determine CML in milk products using ion-exchange chromatography with ninhydrin detection (34). Shortly after this initial report, CML was determined in acid hydrolysates of various food samples via gas-liquid chromatography (GLC). For GLC, various
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