Conditions and Mechanism of Formation of the Maillard Reaction Pigment, Furpenthiazinate, in a Model System and in Some Acid Hydrolyzates of Foods and its Biological Properties.

Furpenthiazinate is a yellow pigment formed by the Maillard reaction between cysteine and furfural under strongly acidic conditions. Here, we describe the conditions and mechanism of pigment formation in a model system and in an acid hydrolyzate of food and analyze its biological properties. A reaction solution containing 32 mM cysteine and 128 mM furfural or 64 mM cysteine and 256 mM furfural in the presence of 2-6 M hydrochloric acid that was heated to 110 °C for 1-2 h yielded approximately 3 mM furpenthiazinate. Nuclear magnetic resonance analysis of furpenthiazinate prepared using 1-13C or 5-13C d-ribose suggests that it was formed through the condensation of cysteine and two C5 chains derived from pentose with the dehydration and elimination of formic acid. Furpenthiazinate was detected in mieki, a seasoning, and some acid hydrolyzates of food, and it did not show antibacterial or mutagenic activity.

Novel Maillard Pigment, Furpenthiazinate, Having Furan and Cyclopentathiazine Rings Formed by Acid Hydrolysis of Protein in the Presence of Xylose or by Reaction between Cysteine and Furfural under Strongly Acidic Conditions.

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.

Two novel pyrrolooxazole pigments formed by the Maillard reaction between glucose and threonine or serine.

Pyrrolothiazolate formed by the Maillard reaction between l-cysteine and d-glucose has a pyrrolothiazole skeleton as a chromophore. We searched for a Maillard pigment having a pyrrolooxazole skeleton formed from l-threonine or l-serine instead of l-cysteine in the presence of d-glucose. As a result, two novel yellow pigments, named pyrrolooxazolates A and B, were isolated from model solutions of the Maillard reaction containing l-threonine and d-glucose, and l-serine and d-glucose, respectively, and identified as (2R,3S,7aS)-2,3,7,7a-tetrahydro-6-hydroxy-2,5,7a-trimethyl-7-oxo-pyrrolo[2,1-b]oxazole-3-calboxylic acid and (3S,7aS)-2,3,7,7a-tetrahydro-6-hydroxy-5,7a-dimethyl-7-oxo-pyrrolo[2,1-b]oxazole-3-calboxylic acid by instrumental analyses. These compounds were pyrrolooxazole derivatives carrying a carboxy group, and showed the absorption maxima at 300-360 nm under acidic and neutral conditions and at 320-390 nm under alkaline conditions.

Formation scheme and antioxidant activity of a novel Maillard pigment, pyrrolothiazolate, formed from cysteine and glucose.

We recently identified 6-hydroxy-3[R],7a[S]-dimethyl-7-oxo-2,3-dihydropyrrolo[2,1-b]thiazole-3-calboxylic acid, a novel pyrrolothiazole derivative carrying a carboxy group and named pyrrolothiazolate, as a Mallard pigment formed from l-cysteine and d-glucose. Here we described the formation of its enantiomer, the plausible formation scheme of pyrrolothiazolate, and its antioxidant activity. When d-cysteine was used instead of l-cysteine in the reaction mixture, the enantiomer of pyrrolothiazolate was obtained. The carbon at position 1 of glucose was incorporated into two methyl groups of pyrrolothiazolate. The pigment was considered to be formed through 1-deoxyglucosone (1-DG). The dehydrated isomer of 1-DG would be condensed with the thiol and amino groups of cysteine. This condensate was dehydrated and cyclized to form pyrrolothiazolate. This compound was an antioxidant showing radical scavenging activity.

Isolation, identification, and formation conditions of a novel Maillard yellowish pigment, pyrrolothiazolate.

We isolated a novel yellow pigment from a model Maillard reaction system containing l-cysteine, l-lysine, and glucose and identified it as 6-hydroxy-3[R],7a[S]-dimethyl-7-oxo-2,3-dihydropyrrolo[2,1-b]thiazole-3-calboxylic acid. This compound was a novel pyrrolothiazole derivative carrying a carboxy group and was named pyrrolothiazolate. This compound showed the absorption maxima at 300 and 360 nm under acidic and neutral conditions, while 320 and 400 nm did under alkaline conditions. Pyrrolothiazolate formed from cysteine and glucose was the major low-molecular-weight Maillard pigment in the reaction mixture, and its formation was stimulated by adding lysine to the reaction cocktail. After heating at 110 °C for 2 h, 1-2 mg/mL of pyrrolothiazolate was formed in a reaction mixture containing 100 mM cysteine, 200 mM lysine, and 300 mM glucose dissolved in 0.5 m acetate buffer (pH 6.0) or 0.5 m phosphate buffer (pH 6.5).