Furan derivatives aromas from

As a rule furan derivatives are considered important aroma constituents from a sensory point of view. They are mainly associated with sweet, fruity, nutty or caramel-like odor-impressions. The furans have no meaty characteristics, but it seems possible that they contribute to the overall odor of broiled and roasted meat. 

A large number of furan derivatives are produced in non-enzymatic browning reactions as dehydration products of carbohydrates and related compounds, such as ascorbic acid (y-lactones can also be considered furan derivatives). Most furans are common to many thermally processed foods. Higher levels of these compounds are also present in acid protein hydrolysates. Furan-2-carbaldehyde has the characteristic pleasant woody aroma resembling nuts, which arises from pentoses and ascorbic acid, and 5-methylfuran-2-carbaldehyde, which is a product of 6-deoxyhexoses. A fatty herbal type flavour is provided by 5-hydroxymethylfuran-2-carbaldehyde arising from hexoses. 2-Acetylfuran arising from hexoses and pentoses is an important component of a number... 

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

In the presence of sulfur compounds (e.g. cysteine) pentoses and methylpentoses produce, in addition to 4-hydroxy-5-methyl-2H-furan-3-one and 4-hydroxy-2,5-dimethyl-2ff-furan-3-one, respectively, related compounds containing sulfur in the molecule. Many of these compounds resemble the aroma of cooked or roasted meat. In the presence of primary amines, 1-deoxyhexo-2,3-diuloses derived from disaccharides yield pyridinium betaines and, further, pyrid-4-ones and isomeric 2-acetylpyrroles. The reaction with secondary amines leads to N-substituted... 

Other important odorous components of foods are fragrant lactones derived from branched aliphatic hydroxycarboxyhc acids. The trivial names are normally preferred. An important component of the aroma of wines and spirits aged in oak barrels (such as whisky) is the so-called whisky lactone, 5-butyl-4-methyl-4,5-dihydro-3H-furan-2-one (3-methyloctano-4-lactone, 3-methyl-4-octanolide or 4-butyl-3-methylbutyrolactone), also known as cognac or oak lactone, which can exist in four stereoisomers, ofwhich the (3S,4S)-isomer (8-106) predominates. In brandy, for example, the content of the (Z)-isomers, (3R,4R)- and (3S,4S)-isomers, that have a desirable flavour, ranges between 30 and 247 xg/l. The (E)-isomers, (3S,4R)- and (3E,4S)-isomers, are found at a concentration of 115-736 p.g/1. The precursor of the (3S,4S)-isomer in oak wood... 

Certain 2-hydroxy substituted y-lactones (3-hydroxy furan-2-ones) derived from ycrotonolactone, however, have a specific odour. Typically 3-hydroxy-4,5-dimethyl-5//-furan-2-one (sotolon) has an aroma resembling fenugreek or curry at higher concentrations, and caramel, maple syrup or burnt sugar at lower concentrations. Sotolon occurs as a mixture of -)- R)-and (-F)-(S)-enantiomers (8-111). The perception threshold of (S)-sotolon (0.8 (xg/1) in a model wine solution was 100 times lower than that of the (l )-enantiomer (89 p-g/l), indicating that mainly (S)-sotolon contributes to the characteristic aroma of wines. The key component of acid protein hydrolysates is the higher... 

Aldehydes and ketones react with ammonia and primary amines to form imines. Reaction with aldehydes yields aldimines, and ketimines arise in reactions with ketones (Figure 8.28). Imines derived from aliphatic carbonyl compounds are generally unstable and are transformed to more stable products, such as amines, diamines and others. Secondary amines react with aldehydes and ketones with the formation of enamines (Figure 8.29). Imines are similarly flavour-active compounds derived from furan-2-carbaldehyde. For example, the aromas of Ar-furfuryl(isobutylidene)amine, N-(furfuryl)isopentyhdeneamine (8-155) and N-(furfurylidene)isobutylamine (8-156) reportedly resemble chocolate. 

The hydrothermolysis (27.5 MPa, 290 - 400 C) of D-fructose furnished 5-hydroxymethyl-2-furaldehyde, furfural, and l,2,4-benzenetriol. The epimeric compounds S3, separable by h.p.l.c., have been isolated in high yields from the reaction of D-glucose with guanosine under physiological conditions. An analysis of the aroma compounds produced on exposure of riramnose to cysteine under roasting conditions (2(X) - 220 C) revealed the presence of ca. 180 compounds, mosdy derivatives of furan, pyrrole, artd thiophene, 125 of which have been identified. ... 

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