Amines, reactions with reducing sugars

Proline is a particular case in the Maillard reaction because it is, unlike other amino acids, a secondary amine. It represents an important precursor for popcom-like aroma compounds in the reaction with reducing sugars such as glucose [46]. The relevant aroma compounds in this reaction are 2-acetyl-l-pyrroline (22), l-(l,4,5,6-tetrahydro-2-pyridyl)-l-ethanone (23) and its isomer l-(3,4,5,6-tetrahydro-2-pyridyl)-l-ethanone (24) [47], The formation pathway (Fig. 3.25) shows the important intermediates 2-oxopropanal (7) and 1-pyrroline (25) [48, 49[. Another amino acid precursor for 22 is ornithine, an amino acid in yeast or yeast extracts [49[. 

Despite the current popularity of the polyphenol theory, a completely satisfactory scheme for the occurrence of humic and fulvic acids in diverse geologic environments has yet to be established. In practice, all pathways may be operative, but not to the same extent in all environments or in the same order of importance. A lignin pathway may-predominate in wet sediments, such as peats and swamps. The drastic conditions existing in soils under a harsh continental climate (e.g., some Mollisols) may favor humus synthesis by sugar-amine condensation. The disappearance of amino acids from buried sediments has been attributed to the formation of brown nitrogenous polyelectrolytes by reaction with reducing sugars (Stevenson, 1974). 

Secondary amines may also interact with reducing sugars. However, the reaction cascade does not proceed beyond the formation of the imine, and thus no coloration develops (22). 

Polyamide microcrystalline powders form measurable polymer-bound fluorescent reaction products with malonaldehyde from oxidizing lipids and with reducing sugars. The compounds form on the terminal amine groups which appear to exist in zwitterionic fields with carboxylate anions, as revealed by titration with acid, alkali, or benzoquinones. 

Hodge J.E., Fisher B.E. and Nelson E.C. (1963) Dicarbonyls, reductones, and heterocyclics produced by the reactions of reducing sugars with secondary amine salts. Am. Soc. Brewing Chemists Proc., 84-92. 

Primary and secondary amines can react readily with aldehydes and more slowly with ketones to give Schiffs bases or enamines, respectively. This reaction is particularly important with reducing sugars such as glucose, lactose and fmctose that may be incorporated in formulations with amines. For instance, if LDOPA were formulated in a tablet with lactose as a filler, the reaction shown in Figure 3.23 could occur. Such reactions, leading to discolouration of lactose-containing tablets, have been... 

Figure 1.114 The reaction of a reducing sugar with an amine-containing compound in the presence of sodium cyanoborohydride results in ring opening with the formation of a secondary amine derivative.

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