Investigation of the Acyclic Forms of Reducing Sugars and Amadori Products by FTIR Spectroscopy

Abstract

The acyclic forms of reducing sugars and Amadori products were studied by FTIR spectroscopy. The spectra of different aldoses and ketoses were recorded as a function of temperature and pH. Fourier self-deconvolution of the carbonyl region (1700 - 1750 cm-1) has revealed that pentuloses, pentoses, and hexuloses exhibit absorption bands at 1733, 1726 and 1717 cm-1 and these bands were tentatively assigned to 3-keto, 2-keto and aldehydo forms of the sugars, respectively, formed through Lobry de Bruyn-Alberda van Ekenstein transformation reactions, whereas, tetruloses showed only two bands at 1733 and 1717 cm-1. In addition, the corresponding 2-deoxy-aldoses showed only one peak. The migration of the carbonyl group of the acyclic forms of reducing sugars can proceed through enediol formation; these species absorb in the region of 1620-1700 cm-1. The sugars that exhibited migration of the carbonyl group also showed an absorption band centered at 1650 cm-1. This band was also sensitive to temperature and pH similar to the carbonyl absorption band and, after treatment of the sugar with ozone or passing a stream of air in the presence of FeCl3, the intensity of the band was diminished, indicating its double bond character.