Caramelization kinetics

Similar anomalous distributions are observed in other thermal product mixtures. A commercial soft caramel made by heating sucrose and 0.1% acetic acid to 160°C contained 18% of a mixture of di-D-fructose dianhydrides.94 fi-D-Fru/-1,2 2,1 - 3-D-Fru/(now assigned as a-D-Fru/-l,2 2,l -a-D-Fru/83), ot-D-Fru/-1,2 2,1 -p-D-Fru/(5), ot-D-Frup-1,2 2,l -0-D-Fnjp (4), ot-D-Fru/-l,2 2,1 - 3-D-Frup (1), and p-D-Fru/-l,2 2,3 - 3-D-Fru/ (2) were found in the ratio 4 12 1 6 2. The first three of these, constituting 68% of the mixture, are considered to be kinetic products. The authors commented on this, but did not offer any explanation. Notice, however, that the preparation of such commercial caramels commences with heating of an acidic aqueous solution of sucrose, which almost certainly results in hydrolysis. Hence, the final dianhydrides are probably derived from the reaction of fructose, rather than sucrose. 

This difference in kinetics was exploited to develop a procedure to determine free and reversibly bound sulfite in food. The mobile phase consisted of an aqueous solution of 0.05 M tetra-butylammonium hydroxide adjusted to the desired pH by the addition of glacial acetic acid (34). Fluorimetric detection is also possible, because a reaction of the formaldehyde-bisulfite complex with 5-aminofluorescein gives a nonfluorescent product. The sulfite is measured indirectly by its suppresion of the fluorescence of the reagent (31). This method is applicable to the determination of S02 at > 10 ppm and is not applicable to dark-colored foods or ingredients where SO, is strongly bound, e.g., caramel color. This method does not detect naturally occurring sulfite. Sulfur dioxide is released by direct alkali extraction. 

E.-H. Ajandouz, L. S. Tchiakpe, F. Dalle Ore, A. Benajiba, and A. Puigserver, Effects of pH on caramelization and Maillard reaction kinetics in fructose-lysine model systems, J. Food Sci., 2001, 66, 926-931. 

The optimal conditions and kinetics of the formation of nondialyzable melanoidins responsible for the brown color of caramel is now under study in various model systems. For the D-glucose-glydne model system at 110°, the rate constants are 4.55 X 10 Vs and 9.40 X 10" /s for the molar sugar amino add ratios 2.5 1 and 1 2.5, respectively. Rates for other... 

Studies of the kinetics of caramelization made by Ramaiah, Agarwal, and coworkers " revealed that, in the beginning, low-molecular-weight prod-... 

The above methodology proved very successful for accessing pure standards of DFAs 5, 7, 10, and 14, which are among the most abundant DFAs in kinetic mixtures of diastereomers as well as in caramel. It is, however, intrinsically limited to compounds having identical ring size at both monosaccharide moieties. Moreover, the di-p-D-fructofuranose l,2 2,l -dianhydride isomer 12 remained elusive. 

The use of phenyl p-o-glucopyranoside as internal standard and authentic samples of DFAs obtained by synthesis allowed determination of the corresponding response factors for quantitative analysis. The relative abundance of DFA diaster-eomers in a D-fructose caramel obtained by heating a concentrated solution of sucrose in the presence of 10% citric acid was found to correspond to a kinetic distribution, the ot-D-fructofuranose p-o-fructofuranose l,2 2,l -dianhydride 10 being the major component in the mixture (Fig. 4). 

Fig. 7 Kinetics of D-fmctose conversion after Lewatit S2328 catalyzed caramelization. The structures of the three major DFAs present in the final product after 2 h with indication of their...

Ajandouz, E. H. and Puigserver, A. (1999). Nonenzymatic browning reaction of essential amino acids Effect of pH on caramelization and Maillard reaction kinetics. / Agric. Food Chem. 47,1786-1793. 

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