Hexoses, Maillard reaction

F. Ledl, J. Hiebl, and T. Severin, Studies on the Maillard reaction. XIX. Formation of coloured P-pyrones from pentoses and hexoses, Z. Lebensm. Unters. Forsch., 1983,177, 353-355 FoodSci. Technol. Abstr., 1985, 17, 2A55. 

T. Hofmann, Acetylformoin — a chemical switch in the formation of colored Maillard reaction products from hexoses and primary and secondary amino acids, J. Agric. Food Chem., 1998, 46, 3918-3928. 

As expected, pentoses react similarly to hexoses in the Maillard reaction, with the formation of 1- and 3-deoxyosones. However, the initial two-carbon fragment formed from the reaction of xylose with alanine is not the glycolal-dehyde expected from retro-aldolisation of the Amadori rearrangement product, but glyoxal, for reasons which are not clear. ... 

Its formation from rhamnose heated with piperidine acetate in ethanol, under the same conditions that produced amino-hexose-reductones from glucose and other hexoses, was described as early as 1963 by Hodge et al., who confirmed the structure by IR and NMR data and proposed a formation pathway. The formation from Amadori intermediates was been reviewed by Vernin (1981). Numerous model systems have confirmed that it is one of the main Maillard-reaction products. For instance we will mention the formation from L-rhamnose and ethylamine (Kato et al., 1972) and from pentose/glycine or alanine, whose mechanism was proposed by Blank and Fay (1996) and Blank et al. (1998), from the intermediate Amadori compound, /V-(l-deoxy-D-pentos-l-yl)glycine. Furaneol is also formed by recombination of... 

As explained by Ledl (1990), this pyranone, which has been detected in many heated or stored foods and results from the ring closure of a hexose, was previously isolated by Severin and Seilmeier (1968) and identified by Mills et al. (1970). It is a Maillard reaction product of glucose and glycine and has a mutagenic activity (Ref. 33 in Hiramoto et al., 1998). 

In addition, other work showed that 3-hydroxy-4,5-dimethyl-2(5H)-furanone can be formed thanks to a Maillard reaction of hexoses and pentoses in the presence of cysteine 20). Due to the non-linear structure of Sotolon, its formation cannot simply be explained directly from sugar cyclization during tire Maillard reaction, like other furanones such as Furaneol. Hence, it is likely tliat Sotolon results from rearrangement of Amadori products of low molecular weight like butan-2,3-dione (diacetyl) and hydroxyacetaldehyde, via an aldol condensation (Figure 6). 

The reaction products of the Maillard reaction, such as l-amino-l-deoxy-2-ketose (Amadori product) or 2-amino-2-deoxyaldose (Heyns product), do not contribute to flavor directly but they are important precursors of flavor compounds [48]. These thermally unstable compounds undergo dehydration and deamination reactions to give numerous rearrangement and degradation products. The thermal degradation of such intermediates is responsible for the formation of volatile compounds that impart the characteristic burnt odor and flavor to various food products. For example, at temperatures above 100 C, enolization products (such as l-amino-2,3-enediol and 3-deoxyosone) yield, upon further dehydration, furfural from a pentose and 5-hydroxy methylfurfural and 5-meth-ylfurfural from a hexose [2]. 

S. Horvat, M. Roscic, and J. Horvat, Synthesis of hexose-related imidazolidi-nones Novel glycation products in the Maillard reaction, Glycoconjug. J., 16 (1999) 391-398. 

Frank and T. Hofmann, On the influence of the carbohydrate moiety on chromophore formation during food-related Maillard reactions of pentoses, hexoses, and disaccharides, Helv. Chim. Acta, 83 (2000) 3246-3261. 

For a Maillard reaction involving glucose the major dicarbonyl intermediate is 3-deoxy-D-erythro-hexose-ulose (also known as 3-deoxyglucosone). Ascorbic acid can also produce many dicarbonyl compounds (Taqui-Khan, 1967 Kurata et al., 1973 Kurata and Fujimaki, 1976 Martell, 1980) via the Maillard reaction including 3-deoxy-D-erythro-hexose-ulose (Hirsch et al., 1992). Ascorbic acid can also lead to 3-deoxy-D-glycero-pentose-2-ulose and D-glycero-pentose-2-ulose. Aldehydic products of the Maillard reaction are able to cross-link proteins. 

As shown in Table III no radicals could be detected clearly demonstrating that the CROSSPY formation was still in the induction period. In order to check the influence of reductones on radical formation, this ftiermally pre-treated mixture was incubated in the presence of ascorbic acid at room temperature. Analysis of the mixture by EPR spectroscopy revealed that instanftmeously after reductone addition the radical cation was generated (Table III). To investigate the effectivity of carbohydrate-derived reductones in CROSSPY formation, in comparative experiments, acetylformoin as well as methylene reductinic acid, both well-known to be formed during thermal treatment of hexoses (19), were added to the thermally pre-treated mixture. Both the Maillard reaction products were found to rapidly induce radical formation, however, in somewhat lower effectivity when compared to ascorbic acid (Table III). 

In the course of the Maillard reaction, de-oxyosones and reductones, e. g., acetylformoin (cf. Ill, Formula 4.67), are formed. They cttn react to give enol and triketo compounds via an addition with disproportionation (Formula 4.86). Redox reactions of this type can explain the formation of products which are not possible according to the reactions described till now. In fact, it has recently been found that, for example, glucose 6-phosphate and fructose-1,6-diphosphate, which occur in baker s yeast and muscle, form 4-hydroxy-2,5-dimethyl-3(2H)-furanone to a large extent. Since the formation from hexoses (or hexose phosphates) is not explainable, reduction of the intermediate acetylformoin (Formula 4.87) must have occurred. As shown, this reduction can proceed through acetylformoin itself or other reductones, e. g., ascorbic acid. Such re-... 

In carbohydrate-containing foods, furan-2-carbaIdehyde is often present, arising from pentoses and ascorbic acid as a dehydration product. Other common furan-derived aldehydes are 5-hydroxymethyIfuran-2-carbaIdehyde (from hexoses) and 5-methyIfuran-2-carbaIdehyde (resulting from 6-deoxyhexoses). Other heterocyclic aldehydes derived from pyrrole, thiophene, pyridine, pyrazine and other heterocyclic compounds are formed as products of the Maillard reaction. 

The chemistry of sucrose has been reviewed. The Maillard reaction of reducing sugars with twenty amino-acids was faster for pentoses than for either hexoses or disaccharides. The reaction was catalysed by organic acids at pH 5—6. Sodium poly(styrene sulphonate) at concentrations of 10 —10 mol 1 inhibited... 

Foods derived from plant materials contain pentose as well as hexose sugars, which are usually formed under weakly acidic conditions. It is well known that pentose contributes more to browning by the Maillard reaction than hexose does, because the oxo-or reducible form of sugars is higher in pentose than in hexose. Hydroxymethylfurfural (HMF) is one of the major decomposed products of such hexoses as glucose and fructose under acidic conditions, while furfural is the corresponding one of pentose and is also formed by the decomposition of ascorbic acid. 

The decomposition or reaction products of hexoses, especially glucose, by the Maillard reaction have been intensively examined. However, there is less data on the reaction products of pentose or furfural. So far some low molecular weight yellow, red or blue pigments formed by the Maillard reaction of furfural or pentose have been reported (Figure For example, a yellow compound (1) was formed by the reaction between... 

Tressl et al7r J1 designated the linear polymers as Type I and the branched ones as Type II. In most melanoidins, they would represent domains (or substructures), unsubstituted pyrroles and Strecker aldehydes, for example, being integrated into the melanoidin backbone, giving a complex macromolecular structure overall. Tressl et aV1 consider the oligomerisation/polycondensation reactions described as the only experimentally established pathways by which simple Maillard products generated from hexoses and pentoses are easily and irreversibly converted into macromolecules. 

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