Amadori compound

The kinetics of the Amadori-compound formation from D-glucose and l-lysine, as well as melanoidin formation, has been examined. The so-called Amadori compounds are formed at an exponential rate, while showing pseudo-first-order disappearance of L-lysine in the presence of... 

Benzing. An amadori compound from tobacco. Carbohydr Res 1981 98 NT567... 

Scheme 12.1 Initial steps in the Maillard reaction showing the formation of an Amadori compound...

The major chloroform extractible product from the decomposition of 1-deoxy-l-dibenzylamino-D-fructuronic acid in pH 6.0 buffer is 4-hydroxy-5-methyl-3(2/7)-furanone [78], Treatment of the same Amadori compound in 2N sulfuric acid gives 2-furaldehyde [79],... 

The Amadori compound which forms in the preliminary stages of... 

The Amadori compound may be degraded via either of two pathways, depending on pH, to a variety of active alcohol, carbonyl and dicarbonyl compounds and ultimately to brown-coloured polymers called melanoidins (Figure 2.31). Many of the intermediates are (off-) flavoured. The dicarbonyls can react with amino acids via the Strecker degradation pathway (Figure 2.32) to yield another family of highly flavoured compounds. 

The pigments of soy sauce, first studied by Kurono and Katsume (100), are melanoidins, which were reported by Omata, et al. (101) to be produced from the reaction of sugars and amino acids. Kato, e a l. (102) found 3-deoxyglucosone as an intermediate in browning of soy sauce (cf. 103). Oxidative browning (104,105) was again reviewed (44) with emphasis on the browning of Amadori compounds and interaction between melanoidins and iron. 

Hashiba, H. The browning reaction of Amadori compounds derived from various sugars. Agric. Biol. Chem. 1982, 47, 547-8. 

Relation of the Free Radical to the Schiff Base, Amadori Compound and 3-Deoxyglucosone ( 5)... 

Amadori compounds (N-substituted-l-amino-l-deoxy-2-ketoses) are potential precursors to the formation of many of these heterocyclic volatile products. The secondary nitrogen in most Amadori compounds is weakly basic and is therefore a likely site for rapid nitrosation reactions via normal reactions with nitrous acid, under mildly acidic conditions. However, purified Amadori compounds are usually obtained only after tedious isolation procedures are invoked to separate them from the complex mixtures of typical Maillard browning systems. Takeoka et al. ( 5) reported high performance liquid chromatographic (HPLC) procedures to separate Amadori compounds in highly purified form on a wide variety of columns, both of hydrophilic and hydrophobic nature. They were able to thus demonstrate that reaction products could be followed for kinetic measurements as well as to ensure purity of isolated products. 

Takeoka et al. (5) also reported methods for derivatizing both aliphatic and aromatic Amadori compounds as -nitrobenzyloxy-amine (PNBO) derivatives to allow facile UV detection in the pico-molar range for HPLC separations. They reported in the same paper a simple method for derivatizing the Amadori compounds to allow gas chromatographic/mass spectrometric (GC/MS) separation and identification of highly purified Amadori compounds. 

Only recently have N -nitroso Amadori compounds been characterized chemically. The first description of an -nltroso derivative of an Amadori compound reported the formation of 1-deoxy-l-(N -nitroso-3,4-xylidino)-D-f ructose to confirm that a secondary amino group had been formed in an Amadori compound ( 6). Coughlin et al. ( 7) and Heyns et al. ( 8) described the formation of nitrosated Amadori compounds. Since Amadori compounds are weakly basic secondary amines and occur widely in Maillard browned foods and beverages ( 5) and unburned tobacco ( ), the genotoxic potential of these compounds is of interest. 

It is well known that the Maillard reaction in foods is initiated by the formation of colorless and tasteless intermediates, which preferentially are formed in low-moisture systems ( ,5.). In this way by reaction of glucose with amino acids fructose-amino acids are formed via Amadori rearrangement of the primary glucosyl-ami-no acids (1 ). Fructose-amino acids e.g. have been isolated from freeze-dried apricots and peaches ( 6,7,8j. Amadori compounds arising from aldoses and amino acids are formed during drying of foods of plant origin and can be easily detected by amino acid analysis (j>). 

It becomes clear that analytical methods based on the evaluation of the end products of deteriorative reactions will not be satisfactory. Therefore in our own experiments amino acid analysis of Amadori compounds and gas chromatography of volatile Strecker aldehydes were applied to detect the onset of the Maillard reaction well before detrimental sensory changes occurred. 

In former experiments (5) we have shown that chemical analysis for Amadori compounds (mainly consisting of fructose-glutamic acid) and isovaleralde-hyde, formed by Strecker degradation of the amino acids leucine and isoleucine, can be used for an early detection of undesirable quality changes caused by the Maillard reaction. In order to demonstrate the usefulness of these compounds as indicator substances for quality improvement of dried products, we performed drying experiments with carrots as an example of plant products. 

For calculation of the molar ratio of Amadori compounds of peak C in the amino acid chromatogram (Figure 1) the following formula was used ... 

Figure 1. Shortened chromatogram of amino acids in air-dried carrots. Peak C represents Amadori compounds formed by reaction between glucose and the amino acids threonine, serine, asparagine, glutamic acid, and glutamine.

Figure 2. Formation of browning intermediates (Amadori compounds corresponding to peak C in Figure 1) and browning during air drying (110 "C) of carrot cubes. Key O, water content related to dry matter 0, product temperature , formation of Amadori compounds (mol %) and A, browning (excitation wavelength 420 nm).

Figure 3. One-step air drying of the carrot variety "Bauer s Kieler Rote at an air temperature of 110 °C. Key , mol % of Amadori compounds corresponding to peak C in Figure 1 , product temperature (°C) and O, water content (%, related to wet matter). The dashed lines are associated with drying to a final water content of 7% guaranteeing a sufficient shelf life.

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