Chemistry of nonenzymic browning. IX. Studies of sugar mono-esters of malic acid found in browned freeze-dried apricots

Abstract

Mono-esters of glucose, fructose, and sucrose were prepared by heating the unsubstituted sugar with DL-malic acid. Chromatographic separations showed that four esters were formed from both glucose and fructose and six from sucrose. Three glucose esters were obtained chromatographically pure and two of these gave brucine salts, one crystalline. Periodate oxidation and acid strengths showed that these esters were glucose 1-α-, 6-α-, and 6-β-hydrogen malates. One fructose ester was obtained chromatographically pure and shown to be fructose 6-α-hydrogen malate. Structures were assigned to the other esters on the basis of their R_Glucose values and acid strengths. Structures, based on the results of partial hydrolysis with acid, were assigned to three sucrose esters. These results yield presumptive evidence for the identity of the malic acid esters detected in freeze-dried fruit (Anet and Reynolds 1957). The acids in freeze-dried fruit were determined by elution chromatography using the formate form of an anion exchange resin. The acids and esters in freeze-dried fruit stored at 25, 37, and 50 °C were similarly determined.