Sugars degradation

After pyruvic acid and acetaldehyde had been identified as intermediate products of glycolysis, sugar degradation could be formulated schematically by the following equations ... 

Ideas regarding the mechanism of phytochemical reduction of olefins have been advanced by Fischer and Eysenbach. They also point out that just as in the case of the simple disproportionations in the course of sugar degradation (for example, the second and third forms of fermentation), saturation of the olefinic linkage is at an optimum in the weakly alkaline range, at about pH 8.5. 

The work which Wohl reported in his earliest paper on sugar degradation had been planned with the expectation that the nitriles of the aldonic acids would react as cyanohydrins. When he carried out his first degradation with pentaacetyl-D-glucononitrile (XXIX) he used ammonia... 

Besides the well-known Maillard reaction, additional reactions like sugar degradation, fat oxidation and interaction of Maillard intermediates are major sources for powerful flavour materials. 

A Stitz, W Buchberger. Determination of sugar, sugar degradation products and alcohols by high-performance liquid chromatography with electrochemical detection. Fresenius J Anal Chem 339 55-57, 1991. 

The sugars in the liquid after pretreatment are partly obtained in oligomer form. To convert the residual oligosaccharides to mono- and disaccharides, the samples were hydrolyzed with 4% H2S04 at 121°C for 10 min. To determine the potential sugar degradation during the acid hydrolysis, the experiments were carried out in triplicate, and known amounts of monosaccharides were added to one of the hydrolysate samples. 

Furans are the most abundant products of the Maillard reaction and they account for the caramel-like odor of heated carbohydrates (8). Some sugar degradation compounds, such as maltol, isomaltol, 4-hydroxy-5-methyl-3(2H)-furanone, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, and 2-hydroxy-3-methyl-2-cyclopentene-l-one (cyclotene), have odors usually described predominantly... 

The experiments have been completed by additional reaction of xylose, fructose and some characteristic sugar degradation products like cyclotene, Furaneol and diacetyl and by thermal decomposition of Ama-dori rearrangement products. It is well knwon that sugars can react with suitable amino compounds very easily. In the course of these reactions sugars are mostly decomposed and brown melanoidins are formed. By-products of these melanoidins are many volatile compounds of characteristic aroma properties. They are also responsible for the well known aromas of heated food like meat, coffee and bread. 

Table IV. Formation of 2-Acetyl-l-Pyrroline (Acp) by Reaction of Proline and Sugars or Phosphorylated Sugar Degradation Products in Dilute Aqueous Solution )...

The results reveal that baker s yeast is a potent source for precursors of 2-acetyl-l-pyrroline. It appears likely that the flavor compound is formed in the yeast cells from proline and dihydroxyacetone phosphate via 1-pyrroline and pyruvaldehyde. This is corroborated by the results of c-labeling experiments which showed that the acetyl group in the Acp stems from a sugar degradation product and that the pyrroline ring was derived from proline. 

Methylcyclopentenolone has a strong caramel-like, maple-like or licorice-like aroma (31j, and was found in browned, dehydrated orange juice at the 1 ppm level (43). Its synergistic flavor effect with other compounds, such as 5-methyl-2-furfural and N-ethylpyrrole- 2-carboxyaldehyde, was reported (43). Although it is present at levels five times below its threshold value, it still impacts on the heat-abused flavor of dehydrated orange juice. This ketone probably results from amine-assisted sugar degradation (45). 

Table 2.5 Colour development and radical formation in binary mixtures of alanine and sugars or sugar degradation products (from Hofmann et al.94)...

Brands and van Boekel124 noticed that there were significant differences between aldoses and ketoses, the latter seeming more reactive in sugar degradation reactions. Whereas Amadori compounds were detected in aldose-casein systems, no such intermediates were found for ketose-casein systems. 

Red 2 exposed to different sugar degradation products at 100 °C gave the following %A values (min) glyceraldehyde, 20 glycolaldehyde, 30 triose reductone, 40, dihydroxyacetone, 50 2-oxopropanoic acid, 60 3-hydroxy-2-butanone, 90 butane-dione, 300 HMF, 450 2-oxopropanal, 1200 acetaldehyde, acrolein, and laevulinic acid, no reaction. 

The volatiles produced by sugar degradation can make an important contribution to flavour. Pyrolysis of glucose at 300 °C allowed 56 compounds to be identified, the main product being l,4 3,6-dianhydroglucopyranose.567 More than 100 volatiles were separated when glucose was heated at 250 °C for 30 min in air or in nitrogen 4-hydroxy-2-pentenoic acid lactone, 1-(2-furyl)propane-l,2-dione, and 3-methyl-cyclopentane-1,2-dione were identified as new products.568... 

The data in Table VI indicate that the aromas developed when sugars and amino acids were heating at 120 and 180°C, were quite different from those produced at 100°C. Noticeable differences exist between aroma notes developed at 120°C and 180°C, this may be attributed to sugar degradation notes which become noticeable in the system heated at 135 C and above. 

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