Sugars model systems, amino acids

Koehler P.E., Mason M.E. and Newell J.A. (1969) Formation of pyrazine compounds in sugar-amino acid model systems. J. Agric. Food Chem. 17, 393-6. 

Clegg (60) studied the nonenzymic browning of lemon juice and reported that the phenomenon was attributable to ascorbic acid rather than sugar-amino acid condensations. She reported that furfural was produced during the. development of browning, but did not consider that it played an important role in the aerobically-produced browning. In model systems that simulated lemon juice, she reported that amino acids in ascorbic systems were major contributors to browning (61). 

It is demonstrated that a great many flavor compounds are formed in both model systems. On the other hand, phenylalanine formed by aldol condensations some special aroma products. Furthermore, the generation of thermal aroma compounds depend on the pH, the sugar/amino acid ratio and the temperature. 

In search for the key intermediates to meat flavor development in heated cysteine-sugar systems, it was found that in addition to thiazolidine derivatives also the tetrahydro-l,4-thiazine derivatives are being formed. These tetrahydro-l,4-thiazines, which are the cyclic form of Amadori compounds of cysteine, have excellent meat flavor precursor properties and are likely to play a prominent part in meat flavor development. Another major pathway to meat flavor development is the reaction of cysteine with the Amadori compounds of other amino acids. Model experiments showed that both pathways are probably of about equal importance for flavor development in boiled meat and process flavorings, this in spite of the low reactivity of cysteine with sugars. It seems that the first pathway is general-acid-catalyzed by the other amino acids, whereas the second pathway is inhibited by cysteine. 

Pyrroles are found in the volatiles of most heated foods [29], although they have received less attention than some other classes of aroma volatiles. Some pyrroles may contribute desirable aromas, e.g. 2-acetylpyrrole has a caramel-like aroma, and pyrrole-2-carboxaldehyde is sweet and corn-like, but alkylpyrroles and ac-ylpyrroles have been reported to have unfavourable odours [22]. Many more volatile pyrroles have been found in coffee than in other foods [30], and they are common products of amino acid-sugar model systems. Pyrroles are closely related in structure to the furans, and they are probably formed in a related manner from the reaction of a 3-deoxyketose with ammonia or an amino compound followed by dehydration and ring closure (cf Scheme 12.2). 

HDF has been identified as reaction product of a thermal treatment of sugars, especially the 6-desoxy sugar rhamnose [90], Analysis of the free sugars in the LMW-fraction revealed fructose-1,6-biphosphate (FBP) as the predominating carbohydrate in the LMW fraction (5.75 g/kg yeast), but no rhamnose was present [88]. To elucidate the contribution of FBP as precursors of HDF in the yeast fraction, the sugar phosphate was thermally degraded under the same conditions as used for the LMW fraction of yeast. The results revealed FBP, as effective precursor of HDF in aqueous model systems at lower reaction temperatures (100°C Table 19). It should be stressed that additions of the amino acids proline or alanine did not increase the concentrations of HDF from the carbohydrates listed in Table 19 (unpublished results). The data implied that FBP which was the predominant carbohydrate in yeast, is the... 

Our approach was different, ambitious, yet simple. The odors of more than 400 model systems drawn from 21 amino acids and 8 sugars, treated under different conditions of temperature and humidity with the inclusion of selected third components, were evaluated by one assessor only. 

Fuzfai Z and Molnar-Perl I, Gas chromatographic-mass spectrometric fragmentation study of flavonoids as their trimethylsilyl derivatives Analysis of flavonoids, sugars, carboxylic and amino acids in model systems and in citrus fruits. J Chromatogr A 1149 88-101 (2007). 

A thorough study of the aromas produced from over 400 model Maillard reaction systems vas performed (44). Combinations of 21 amino adds and 8 sugars were evaluated under different conditions of temperature and humidity. Table II lists beefy or meaty aromas produced from thermal interactions between glucose and eight amino acids. 

According to Rizzi,182 the types of systems studied are conveniently divided into simple model systems of reducing sugars and amines or amino acids, sugars and proteins, and sugars by themselves (i.e., caramelisation). Each of these will now be considered in turn, bearing in mind, in particular, the key question of whether the backbone of the polymeric material itself is coloured or whether the colour resides in moieties attached to an essentially colourless backbone. 

Model Systems of Reducing Sugar and Amines or Amino Acids... 

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