Amadori compound, formation

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... 

Table 1. Likens-Nickerson extraction of mixtures of cysteine with carbonyl compounds under optimum conditions for Amadori compound formation ...

R. Badoud, L. Fay, F. Hunston, and G. Pratz, Periodate oxidative degradation of Amadori compounds. Formation of V -carboxymethyllysine and... 

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

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. 

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>). 

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).

In Figure 9 the formation of Amadori compounds dependent on water content is presented for three different carrot varieties (heating time 20 h at 55 C). 

Figure 9. Formation of Amadori compounds in different varieties of carrots by heating for 20 h at 55 °C, dependent on water content. Key O, Pariser Markt 0, Kundulus and A, Bauer s Kieler Rote.

The initial stages of the Maillard Reaction deals with the condensation of amino acids, peptides or proteins with reducing sugars. The reaction occurs with the application of heat with the formation of an "Amadori compound" (See Chapter 1 of this book). 

It appears that both JL, and 3 are produced as intermediates during the decomposition of an Amadori compound. There is little evidence, based on end product isolation that the 4-deoxyosone (2) is produced to any extent in these reactions. An early isolation of 1, by Anet (6), was accomplished by decomposing an Amadori compound ("difructose glycine") in aqueous solution. Subsequent studies have shown that Amadori compounds are easily converted to HMF in dilute acid solution as well. Furthermore, Kato s (8) published preparation of 3-deoxyosone, in which glucose is reacted with N-butyl amine almost certainly involves the intermediate formation of an Amadori compound and its decomposition in situ. Thus, it can be reasonably concluded that 3-deoxyosones are produced from Amadori compounds during their degradation. 

The furan isomaltol (7) and the pyran maltol ( 8 ) (Scheme 3) are consistent with having been formed via a 1-deoxyosone intermediate. Cyclization of such an intermediate and the loss of 2 additional moles of water allow one to arrive at these structures. Data which supports this is found in papers by Hodge and his group (1 3), who synthesized 1-deoxy-l-piperidino-maltulose (J5, Scheme 4) and showed that on further heating, it was converted to galactosyl isomaltol (JJJ). This is convincing evidence that isomaltol is sugar derived and is produced from an Amadori compound. Furthermore, the structure is wholly consistent with the formation of a 4-0-substituted 1-deoxyosone as an intermediate in the reaction. 

Hodge et al. (45) discussed mechanisms for formation of methyl furanones and related substances from Amadori compounds. They have been produced by heating D-ribose and D-ribose phosphate with ammonia (46 47). Hicks and Feather (48) demonstrated that the Amadori compound 1-benzylamino-l-deoxy-D-threo-pentulose dehydrates to 4-hy-droxy-5-methyl-3(2H)-furanone and it has also been identified as a degradation product of L-ascorbic acid. This compound is believed to be formed from ribose-5-phosphate, and gained prominence when it was isolated from beef by Tonsbeck et al. (49). It became more apparent as a precursor of meat flavor when Van den Ouweland and Peer (50) reacted it and its thio analog with HaS to produce a number of sulfur compounds, some of which had meaty odors. 

Furfural identified in beef diffusate appears to be a prominent meat flavor intermediate. It is a dehydration product of pentoses similar to formation of hydroxy methyl furfural from hex-oses. These compounds are formed by dehydration of 1,2-enediols derived from deamination of Amadori compounds (51). 

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