Fructose reaction with amino acids

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>). 

The most efficient method for the clean hydrolysis of sucrose is by the use of invertase, leading to an equimolar mixture of glucose and fructose (invert sugar). The presence of salts increases the rate of thermal degradation of sucrose.337 The reaction is also possible in the presence of such heterogeneous acidic catalysts as zeolites.338 The hydrolysis of the glycosidic bond is the first step of a number of subsequent reactions that can occur on the glucose and fructose residues, such as dehydrations, combinations with amino acids (Maillard reaction), and many other chemicals or fermentation processes.339... 

Lipid oxidation products and their reaction products with amino acids (proteins) have a considerable influence on the typical odour and taste of meat. Particularly significant aminocarboxylic acids include glutamic acid, alanine, threonine and lysine, guanidine compounds (creatine and creatinine), quaternary ammonium compounds (choline and carnitine), peptides (P-alanylhistidine peptides and some products of proteolysis), free nucleotides, nucleosides and their bases (especially inosine 5 -monophosphate, IMP), proteins, carboxylic acids (especially lactic acid), sugars (mainly glucose, fructose and their phosphates, ribose formed by hydrolysis of free nucleotides) and some vitamins (especially thiamine). Some of these compounds, such as glutamic acid and IMP, are additionally used as food additives, namely as flavour enhancers. 

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. 

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