ABSTRACT
A novel Maillard pigment having partial structures of furan and cyclopentathiazine, named furpenthiazinate, was isolated and identified. Although this pigment was found in an acid hydrolysate of a Maillard reaction solution between soy protein and xylose, the same pigment was also formed by the Maillard reaction under strongly acidic conditions between soy protein and xylose and cysteine and furfural. The structure of its reduced form by NaBH4 was determined by MS, NMR, and X-ray analysis and identified as 7-(2-furanyl)-2,3,4,4a,5,6-hexahydrocyclopenta[ b][1,4]thiazin-4-ium-3-carboxylate, indicating that the chemical structure of furpenthiazinate is 7-(2-furanyl)-2,3,5,6-tetrahydrocyclopenta[ b][1,4]thiazine-3-carboxylic acid. Furpenthiazinate showed an absorption maximum at 400 nm and strong yellow color under acidic and neutral conditions. The color contribution of furpenthiazinate was estimated to be more than 60% in a reaction solution prepared from cysteine and furfural.
Subject(s)
Cysteine/chemistry , Furaldehyde/chemistry , Furans/chemistry , Pigments, Biological/chemistry , Soybean Proteins/chemistry , Thiazines/chemistry , Xylose/chemistry , Acids , Hydrogen-Ion Concentration , Hydrolysis , Maillard Reaction , Molecular StructureABSTRACT
Our group has recently isolated and identified novel yellow compounds named dilysyl-dipyrrolones A (DPL A; 1) and B (DPL B; 2) in a heated aqueous solution containing xylose and lysine under weakly acidic conditions. In this study, we isolated and identified a novel DPL derivative (DPL C; 3), which has the same structure as DPL B, except for containing a hydroxymethyl group. To estimate the formation mechanism of DPL derivatives, (13)C-labeled DPLs were prepared and analyzed with LC/MS and NMR. (13)C-labeling experiments using [1-(13)C] ribose showed that the formation pathway of DPL C was different from those of DPLs A and B. In addition, (13)C-labeling experiments using [u-(13)C5] ribose and [1-(13)C] lysine showed that C-6 of a methine moiety in DPL C was derived from C-5 of ribose or acetic acid in buffer. Based on these results, we postulated the formation mechanism of DPLs. We then showed that DPLs A and B had potent antioxidant activities.
