Verhalten von Amadori-Verbindungen w�hrend der Kakaoverarbeitung: 1. Bildung und Abbau von Amadori-Verbindungen

The Maillard reactions: Pathways, consequences, and control

The century old Maillard reactions continue to draw the interest of researchers in the fields of Food Science and Technology, and Health and Medical Sciences. This chapter seeks to simplify and update this highly complicated, multifaceted topic. The simple nucleophilic attack of an amine onto a carbonyl group gives rise to a series of parallel and subsequent reactions, occurring simultaneously, resulting into a vast array of low and high mass compounds. Recent research has focused on: (1) the formation and transformation of α-dicarbonyl compounds, highly reactive intermediates which are essential in the development of the desired color and flavor of foods, but also lead to the production of the detrimental advanced glycation end products (AGEs); (2) elucidation of the structures of melanoidins in different foods and their beneficial effects on human health; and (3) harmful effects of AGEs on human health. Considering that MRs have both positive and negative consequences, their control to accentuate the former and to mitigate the latter, is also being conscientiously investigated with the use of modern techniques and technology.

Flavor formation and character in cocoa and chocolate: a critical review

Chocolate characters not only originate in flavor precursors present in cocoa beans, but are generated during post-harvest treatments and transformed into desirable odor notes in the manufacturing processes. Complex biochemical modifications of bean constituents are further altered by thermal reactions in roasting and conching and in alkalization. However, the extent to which the inherent bean constituents from the cocoa genotype, environmental factors, post-harvest treatment, and processing technologies influence chocolate flavor formation and relationships with final flavor quality, has not been clear. With increasing speciality niche products in chocolate confectionery, greater understanding of factors contributing to the variations in flavor character would have significant commercial implications.

Gas chromatographic determination and mechanism of formation of D-amino acids occurring in fermented and roasted cocoa beans, cocoa powder, chocolate and cocoa shell

Fermented cocoa beans of various countries of origin (Ivory Coast, Ghana, Sulawesi), cocoa beans roasted under defined conditions (100-150 degrees C; 30-120 min), low and high fat cocoa powder, various brands of chocolate, and cocoa shells were analyzed for their contents of free L-and D-amino acids. Amino acids were isolated from defatted products using a cation exchanger and converted into volatile N(O)-pentafluoropropionyl amino acid 2-propyl esters which were analyzed by enantioselective gas chromatography mass spectrometry on a Chirasil-L-Val capillary column. Besides common protein L-amino acids low amounts of D-amino acids were detected in fermented cocoa beans. Quantities of D-amino acids increased on heating. On roasting cocoa beans of the Forastero type from the Ivory Coast at 150 degrees C for 2 h, relative quantities of D-amino acids approached 17.0% D-Ala, 11.7% D-Ile, 11.1% D-Asx (Asp + Asn), 7.9% D-Tyr, 5.8% D-Ser, 4.8% D-Leu, 4.3% D-Phe, 37.0% D-Pro, and 1.2% D-Val. In cocoa powder and chocolate relative quantities amounted to 14.5% D-Ala, 10.6% D-Tyr, 9.8% D-Phe, 8.1% L-Asx, and 7.2% D-Ile. Lower quantities of other D-amino acids were also detected. In order to corroborate our hypothesis that D-amino acids are generated from Amadori compounds (fructose amino acids) formed in the course of the Maillard reaction, fructose-L-phenylalanine and fructose-D-phenylalanine were synthesized and heated at 200 degrees C for 5-60 min. Already after 5 min release of 11.7% D-Phe and 11.8% L-Phe in the free form could be analyzed. Based on the data a racemization mechanism is presented founded on the intermediate and reversible formation of an amino acid carbanion in the Amadori compounds.

Formation of amines and aldehydes from parent amino acids during thermal processing of cocoa and model systems: new insights into pathways of the strecker reaction

A method based on a derivatization with dansyl chloride and LC-MS-MS determination was developed for the quantitation of 2-methylbutyl-, 3-methylbutyl-, 2-phenylethyl-, 3-(methylthio)propyl-, and 2-methylpropylamine. Its application on unfermented, fermented, and roasted cocoas from Ghana and Sulawesi revealed an increase of all amines, except the 3-(methylthio)propylamine, during cocoa fermentation, suggesting an enzymic formation from the parent amino acids isoleucine, leucine, phenylalanine, and valine. However, a much more pronounced formation of most of the amines was measured after roasting of the cocoa, leading to concentrations in the milligrams per kilogram range. This result suggested a new "thermogenic" formation pathway of "biogenic amines". A comparison of the amounts of the amines and the aldehydes in roasted cocoa revealed similar concentrations, for example, for 2- and 3-methylbutanal and the respective amines, whereas the amounts of 2-phenylethylamine were much higher as compared to the amounts of phenylacetaldehyde. Strecker-type model systems, in which each parent amino acid was reacted with 2-oxopropanal, revealed the formation of both the amine and the aldehyde; however, in contrast to cocoa, the concentrations of the aldehydes were always much higher as compared to the amines. The results showed for the first time the thermally induced generation of "biogenic amines" from amino acids. Possible reasons for the different ratios of amines versus aldehydes formed during the roasting of cocoa or the model systems, respectively, are discussed.

Contribution of mass spectrometry to the study of the Maillard reaction in food

The Maillard reaction or non-enzymatic browning corresponds to a set of reactions occurring between amines and carbonyl compounds, especially reducing sugars. The Maillard reaction is known to occur in heated, dried, or stored foods and in vivo in mammalian organisms. In food, the Maillard reaction is responsible for changes in colour, flavor, and nutritive value but also for the formation of stabilizing and mutagenic compounds. Because of the complexity of the Maillard reaction, mass spectrometry, coupled or not to separation techniques, is a key tool in this research area and we will review in this article the contribution of mass spectrometry to the understanding of this reaction. Different steps of Maillard reaction will be described and the importance and the role played by mass spectrometry will be highlighted. In addition, different approaches to investigate the Maillard reaction from the formation of Amadori products (early Maillard reaction product) to the flavor and melanoidin production will also be covered.

Analysis of Amadori Compounds by High-Performance Cation Exchange Chromatography Coupled to Tandem Mass Spectrometry

High-performance cation exchange chromatography coupled to tandem mass spectrometry or electrochemical detection was found to be an efficient tool for analyzing Amadori compounds derived from hexose and pentose sugars. The method allows rapid separation and identification of Amadori compounds, while benefiting from the well-known advantages of mass spectrometry, such as specificity and sensitivity. Glucose- and xylose-derived Amadori compounds of several amino acids, such as glycine, alanine, valine, leucine/isoleucine, methionine, proline, phenylalanine, and glutamic acid, were separated or discriminated using this new method. The method is suitable for the analysis of both model reaction mixtures and food products. Fructosylglutamate was found to be the major Amadori compound in dried tomatoes (approximately 1.5 g/100 g) and fructosylproline in dried apricots (approximately 0.2 g/100 g). Reaction of xylose and glycine at 90 degrees C (pH 6) for 2 h showed rapid formation of xylulosylglycine (approximately 12 mol %, 15 min) followed by slow decrease over time. Analysis of pentose-derived Amadori compounds is shown for the first time, which represents a major breakthrough in studying occurrence, formation, and decomposition of these labile Maillard intermediates.

Synthesis and sensory characterization of novel umami-tasting glutamate glycoconjugates

Two glycoconjugates of glutamic acid, namely, the N-glycoside dipotassium N-(d-glucos-1-yl)-l-glutamate (1) and the corresponding Amadori compound N-(1-deoxy-d-fructos-1-yl)-l-glutamic acid (2), have been synthesized in yields of 35 and 52%, respectively, using new Maillard-mimetic approaches, and their chemical structures have unequivocally been elucidated by 1D- and 2D-NMR and MS experiments. Systematic sensory studies revealed that both glycoconjugates exhibit pronounced umami-like taste with recognition taste thresholds of 1-2 mmol/L, close to that of monosodium glutamate (MSG). Contrary to an aqueous solution of MSG, 1 does not show the sweetish and slightly soapy by-note, but evokes an intense umami taste. Aqueous solutions of 2 were described by the descriptors umami, seasoning, and bouillon-like. Added to a bouillon base, which did not contain any taste enhancers, both glycoconjugates imparted a distinct umami character similar to the control sample containing the same amount of MSG on a molar basis. To the best of our knowledge, these types of glycoconjugates in general and, in particular, N-glucosyl glutamate and N-deoxyfructosyl glutamate have never been reported as taste active compounds having umami-like properties. Therefore, 1 and 2 represent a new class of umami-type taste compounds showing properties similar to the umami reference compound MSG. Systematic (13)C NMR measurements revealed that 1 was fairly stable in aqueous solutions under alkaline conditions (pH 8-10) as well as in dry form. However, it rapidly hydrolyzes in neutral and acidic solutions, giving rise to glucose and glutamate. In contrast, glycoconjugate 2 was observed to be rather stable in aqueous solution as well as in the presence of human saliva.

[Heat-induced decomposition of disaccharide Amadori compounds in quasi-water-free reaction conditions]

The thermally induced decomposition of disaccharide Amadori compounds has been compared to those of monosaccharide ones under almost water-free conditions. The structure of the synthesized maltulosyl compound has been proved to be 4C1-alpha-D-glucopyranosyl- (1----4)-2C5-beta-D-fructopyranosylglycine by 1H- and 13C-NMR spectroscopy. The decomposition of Amadori compounds has been used to study the kinetics of the browning reaction. Compared to fructosylglycine and maltotriulosylglycine, the browning of the disaccharide is faster. Curie point pyrolysis at 300 degrees C and investigation of the pyrolysate by gas chromatography/mass spectrometry have shown that the disaccharide component influences the thermal process. Furanes and furanones have been detected as predominant degradation products, the main one being 2(5H)-furanone. For the first time, we suggest a reaction pathway for the formation of these products via the Maillard reaction which includes 1,6-anhydroglucose.