Isomaltol

Contrast this value with that for the furanone analogue isomaltol, for which log P3 = 14.5 (Ref (76)). 

Thermolysis of D-fructose in acid solution provides 11 and 2-(2-hydrox-yacetyl)furan (44) as major products. Earlier work had established the presence of 44 in the product mixtures obtained after acid-catalyzed dehydrations of D-glucose and sucrose. Eleven other products were identified in the D-fructose reaction-mixture, including formic acid, acetic acid, 2-furaldehyde, levulinic acid, 2-acetyl-3-hydroxyfuran (isomaltol), and 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2//)-furanone (59). Acetic acid and formic acid can be formed by an acid-catalyzed decomposition of 2-acetyl-3-hydroxyfuran, whereas levulinic acid is a degradation prod-uct of 11. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one has also been isolated after acid treatment of D-fructose.The pyranone is a dehydration product of the pyranose form of l-deoxy-D-eo f o-2,3-hexodiulose. In aqueous acid seems to be the major reaction product of the pyranone. 

Hydroxy-2-methyl-4//-pyran-4-one (maltol) and 2-acetyl-3-hydroxy-furan (isomaltol) are also products of the Maillard reaction. Both have a considerable history, due to their early detection in beer and breads. A mechanism based upon the pyranose form of a methyl-a-dicarbonyl inter-... 

Compound 10 cannot undergo further dehydration without first rearranging to the 3,4-enediol (14). The reaction of 14 would yield 2-acetyl-3-hydroxyfuran (isomaltol, 16), a compound produced in low... 

The major products formed from hexoses that react in aqueous acidic solution are 5-(hydroxymethyl)-2-furaldehyde, levulinic acid, and polymeric materials. In addition, many minor dehydration products are found. In a study41 of D-fructose, 2-(2-hydroxyacetyl)furan (13), 2-acetyl-3-hydroxyfuran (isomaltol 16), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, and 3,4,5-trihydroxy-3,5-hexadien-2-one (acetylformoin) were identified. Products not formed solely by dehydration mechanisms include acetone,56 formaldehyde, acetalde-... 

When allowed to react in an almost anhydrous medium (the only water being that produced during the dehydration reaction), compound 51 was found to form maltol (52) and isomaltol (16) in proportions varying with the reagents.88 In aqueous acidic solution, these products and acetylformoin (53) would all be expected from 50 or 51, dependent on whether or not the ring opened and the manner in which the opening occurred. The presence of 49 accounts for compounds 51, 52, 53, and 16, that are frequently detected as products of the degradation of D-fructose, particularly when amines are present. 

The formation of maltol from 2-acetyl-3-methoxyfuran via isomaltol O-methyl ether (428) involves a related method. 

Dehydration results in the formation of important flavor compounds such as 2-furaldehydes (furfural), a formylpyrrole, and similar compounds. Another pathway possibly beginning with the 2 3 enediol involves the enolic form of a l-deoxy-2,3-dicarbonyl intermediate or an equilibrium enolic form which leads to formation of flavor compounds such as methylfuranones, isomaltol, and maltol... 

Furans are the most abundant products of the Maillard reaction and they account for the caramel-like odor of heated carbohydrates (8). Some sugar degradation compounds, such as maltol, isomaltol, 4-hydroxy-5-methyl-3(2H)-furanone, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, and 2-hydroxy-3-methyl-2-cyclopentene-l-one (cyclotene), have odors usually described predominantly... 

The furan isomaltol (7) and the pyran maltol ( 8 ) (Scheme 3) are consistent with having been formed via a 1-deoxyosone intermediate. Cyclization of such an intermediate and the loss of 2 additional moles of water allow one to arrive at these structures. Data which supports this is found in papers by Hodge and his group (1 3), who synthesized 1-deoxy-l-piperidino-maltulose (J5, Scheme 4) and showed that on further heating, it was converted to galactosyl isomaltol (JJJ). This is convincing evidence that isomaltol is sugar derived and is produced from an Amadori compound. Furthermore, the structure is wholly consistent with the formation of a 4-0-substituted 1-deoxyosone as an intermediate in the reaction. 

The finding that the furanone is produced from an Amadori compound was interesting in that it permitted us to test, for the first time, the effect of pH on the products of the reaction. This is not possible using a hexose- derived Amadori compound, because the end products are not stable. The product of 1,2-enolization (3-deoxyosone intermediate) is HMF, which is stable, but the product derived from 2,3 enolization (1-deoxyosone intermediate), maltol and isomaltol are not stable in aqueous solution and thus cannot be detected and measured accurately. In our experiment (Scheme 6), we prepared 1-deoxy-dibenzylamino (13), and -benzylamino (12) D-fructuronic acids, as well as... 

Maltol and isomaltol (1 and 2 in Figure 1) enhanced the fresh bread character of yeast rolls (6) when added at a level of 0.1 %. Other workers (7.) showed that 2-acetyl-l,4,5,6-tetrahydropyridine (3 in Figure 1) restores a cracker-like aroma to bread when added at a level of 6 mg/kg. In the pure state this chemical displays a cracker-like aroma and an odor threshold of 1.6 jig/kg (8). 

The odor of isomaltol is described as sweet, but with a burnt sugar and fruity character (H) 2-Acetylfuran and 2-hydroxyacetylfuran impart burnt sweetish flavors. Furfuryl alcohol and 5-methyl-2-furaldehyde have sweet caramellic flavors (31). The major formation route to most furans in heated-abused citrus products has been postulated as acid-catalyzed enolizations and dehydrations of sugars (38). Furans, such as 2-hydroxyacetylfuran and isomaltol... 

Furfuryl alcohol 2-Hydroxyacetyl furan 5-Hydroxymethyl furfural Isomaltol... 

Isomaltol Fruity caramel, fresh bread odor, overtone medicinal grassy (99) ... 

Another group of compounds that have been related to the aroma of heated foods is the furanones. Teranishi (1971) summarized the findings on several of the furanones (see Figure 7-23). The 4-hydroxy-2,5-dimethyl-3-dihydrofuranone (1) has a caramel or burnt pineapple odor. The 4-hydroxy-5-methyl-3-dihydrofuranone (2) has a roasted chicory root odor. Both compounds may contribute to beef broth flavor. The 2,5-dimethyl-3-dihydrofuranone (3) has the odor of freshly baked bread. Isomaltol (4) and maltol (5) are products of the caramelization and pyrolysis of carbohydrates. 

The first method uses 3-iodofuran as starting material, which is not readily accessible. The other uses isomaltol, which can be prepared from lactose in two steps. The longer method, on the other hand, goes via stages which are reproducible, and according to our experience the yields are satisfactory. 3,4-Dimethoxyfuran shows a very high diene activity which has been mentioned in Section IV, B. 

---