Sucrose thermal degradation

Under the conditions corresponding to the roasting of coffee, serine, threonine, and sucrose yield various substituted pyridines (51), furans, and furanones (52). Thirty-three pyridine derivatives were identified by Baltes and co-workers (51), Recently, 3-methylthiomethylpyridine was identified as one of the products of thermal degradation of the glucose-methionine Amadori intermediates (53). 

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... 

G. N. Richards and F. Shafizadeh, Mechanism of thermal degradation of sucrose. A preliminary study, Aust. J. Chem., 31 (1978) 1825-1832. 

G. Eggleston, J. R. Vercellotti, L. A. Edye, and M. A. Clarke, Effects of salts on the initial thermal degradation of concentrated aqueous solutions of sucrose, J. Carbohydr. Chem., 15 (1996) 81-94. 

Early researchers (24.251 identified 5-hydroxymethyl furfural from sucrose solutions heated above 150°C. Later reports (26.271 listed a series of aliphatic and aromatic carbonyl compounds identical to those associated with the thermal degradation of monosaccharides. 

The products of caramelization are distributed between volatile and nonvolatile fractions. The composition of the volatile firaction is pretty well characterized, contrary to that of the nonvolatile fraction. Thus, neither is the structure of all compounds formed precisely known, nor are the processes which occur understood in detail (see, for instance, a review by Orsi ). The composition of the volatile fraction from the thermolysis of sucrose is the best recognized. The profound decomposition products from the decomposition in vacuo of sucrose arc water, carbon monoxide, carbon dioxide, formaldehyde, acetaldehyde, methanol, and ethanol. The detailed rates and temperature relationships suggest that, with the possible exception of ethanol, the other products result from secondary reactions of dehydration products. The low-molecular-weight portion of the nonvolatile fraction of the thermal degradation of sucrose contains D-fhictose, D-glucose,... 

It was identified in the products of thermal degradation of glucose (Heyns et al., 1966a Walter and Fagerson, 1968), in the model reaction cysteine xylose (Ledl and Severin, 1973), and in model reactions of serine and threonine with sucrose (as well as in coffee) by Baltes and Bochmann... 

It was formed from the thermal degradation of glucose (Heyns et al., 1966a Fagerson, 1969). Baltes and Bochmann (1987a) found 2-and 3-vinylfurans in model reactions involving serine, threonine and sucrose. Only the 2-vinyl isomer was present in coffee. 

Pyridines have been identified among the pyrolysis products of model reactions involving amino acids and sugars, for instance by Ledl and Severin (1973), Mussinan and Katz (1973), and Baltes and Bochmann (1987d). The latter authors identified 15 pyridines present in coffee flavor, 13 of them also being present in reactions of serine and/or threonine, with or without sucrose, under coffee-roasting conditions. Pyridines can also be formed by thermal degradation of Amadori intermediates (van den... 

Heating sucrose to 300°C in a stream of nitrogen produces volatile furan compounds namely 2-methyl furan, furan, 2-hydroxyacetyl furan, and other volatile reaction products (methanol, acetone, acrolein, propanol, and acetaldehyde) [230]. A major compound (2-furfural) and volatile thermal degradation products (2-furyl methyl ketone, 2-furyl propyl ketone, methyl-benzo( )furan, and 5-methyl-3-hydro-furan-2-one) were identified by heating sucrose in an open evaporation dish at 180°C for 90 min [233]. 

Table 1. Major ion fragments for the gasses derived from the thermal degradation of the condensation product of sucrose and diphenyltin dichloride...

---