Search

In the course of the Maillard reaction, labile sugar degradation products are formed that are susceptible to secondary reactions and therefore have a decisive influence on the product spectrum. Such reactive intermediates may be transformed into stable derivatives with trapping reagents, and thus be protected from further reactions. Secondary processes may also be forestalled if the primary products are removed from the reaction mixture by high-vacuum distillation. By this procedure, 5-hydroxymethyl- and 5-(1,2-dihydroxyethyl)-3(2H)-furanone have been identified directly from Maillard reaction mixtures for the first time. The activated methylene group of these 3(2H)-furanones can easily enter into condensation reactions. The coloured condensation products in turn react with primary amines to pyrrolinone derivatives, which may also contribute to the colouring observed in non-enzymatic browning.

Through the Maillard reaction, occurring in food and in the human body, reducing sugars, amino acids and proteins are transformed. Some general and also specific degradation pathways for pentoses, mono- and disaccharides can be defined. The structures of the products are influenced by the type of amine (primary or secondary). During the degradation reactions C-C fissions of the sugars and amino acids (Strecker degradation) can be observed. Some Maillard products are suited as indicator substances to determine the extent of the Maillard reaction.

From a glucose/glycine reaction mixture acids, esters and lactones were isolated and identified. Sugar degradation products could also be determined as benzimidazole derivatives after reaction with o-phenylenediamine. Results derived from model systems suggested possible reaction pathways leading to some of the isolated substances. A lactic acid ester is formed as a product of an unstable beta-pyranone intermediate. A 3-deoxyhexosone serves as a precursor of two furanolactones.

Reactions between glucose and bovine serum albumin proceed predominantly at the side chain amino groups of lysine residues. Among other products, protein-bound 2-formyl-5-(hydroxymethyl)pyrrole-1-norleucine is formed. After alkaline hydrolysis and fractionation of the protein hydrolysate on RP-18 material this substance can be separated by high-performance liquid chromatography. The identity of the norleucine derivative with a synthesized compound can be determined with fast atom bombardment-mass spectrometry spectral data. A colour reaction with thiobarbituric acid is also suitable for detection.

During the thermal decomposition of cysteine, cystine, N-acetylcysteine, 4-thiazolidinecarboxylic acid, cysteine methyl ester, in soy bean oil at 200 degrees C, a series of compounds containing sulphur are formed. Besides 15 alkylthiazoles, -thiazolines and -thiazolidines, compounds with 2 and 3 S-atoms can also be identified: ethane-1,2-dithiole, diethyldisulfide, diethyltrisulfide, 2-methyl-1,3-dithiolane, 1,2-dithiane, thialdine, 1,2,4-trithiolanes, 1,2,4-trithianes and 2-methyl-thiazolidino-(3,4-b-)-thiazolidine. N,N'-dibutyrylcystamine shows an antioxidant effect.

A complex mixture of compounds possessing an intensive aroma of onions is obtained, when propionaldehyde, propionaldehyde and acetaldehyde are treated with hydrogen sulfide and ammonia. Dihydrodithiazines, diethyltrithiolane, diethyl-methyl-1,3-dithiine and in small quantities diethyltetrathiane, dimethylthiophene, dipropyldisulfide, dipropenylsulfide, alkylpyridines, and the condensation products of aldehydes can be proved by the GC-MS-technic. The compositions of the synthetic onion aroma corresponds slightly with the composition of the natural onion aroma.

By means of polarography a new Maillard product (5a) was detected in heated milk. The compound was isolated from a glycine/lactose mixture, which had been heated in buffer at pH 6,8, and then freeze dried by extraction with ethylacetate/methanol. According to its spectroscopic properties, 5a is 4-0-beta-D-galactopyranosyl-2-hydroxy-2-methyl-2H-pyran-3-(6H)-one. Though the amount of 5a formed during heat treatment of milk corresponds to the severity of heat stress, the usefulness of 5a as an indicator with respect to intensity of heat treatment is limited. 5a is rather rapidly converted to galactosyl isomaltol; also unknown peaks develop in the polarogram.

From reaction mixtures of reducing sugars with primary and secondary amines many heterocyclic and carbocyclic compounds have been separated. From the structures of these substances together with the knowledge about reactive intermediates some degradation pathways can be proposed. Caused by the nature of the sugar (pentose, mono- or disaccharide) and the amine (primary or secondary) differences in the pathways are observed. An attempt is made to present some reactions with emphasis to the Maillard reaction in mammalians.

A large number of volatile compounds are formed when onions are heated in butter. More than 120 compounds could be identified with GC-MS-technic. The majority of the substances is not characteristic for the onion aroma. Compounds formed according to a patented production of onion aroma could not be identified.