Strawberry furanones

Synonyms Alletone Alnose Dimethylhydroxy furanone 2,5-Dimethyl-4-hydroxy-3-furanone 2,5-Dimethyl-4-hydroxy-3-(2H)-furanone Furaneol 3(2H)-Furanone, 2,5-dimethyl-4-hydroxy- Pineapple ketone Strawberry furanone... 

Stractan. See Arabinogalactan Straight-run kerosene Straight-run kerosine. See Kerosene Strained honey. See Honey Stratos . See Cycloxydim Strawberry aldehyde. See Ethyl methylphenylglycidate Strawberry furanone. See 4-Hydroxy-2,5-dimethyl-3(2H) furanone Strawberry tree extract. See Arbutus unedo extract... 

An important compound is 4-hydroxy-5-methyl-2H-furan-3-one, known as norfuraneol. Norfuraneol occurs in caramel, roasted chicory root and also in meat broth. 4-Hydroxy-2,5-dimethyl-2H-furan-3-one, known as furaneol, strawberry furanone or pineapple furanone, arises in the Maillard reaction from L-rhamnose (Figure 4.39) and in a reaction of methylglyoxal with hydroxyacetone (Figure 4.41). It occurs, for example, in strawberries, pineapple, roasted almonds, popcorn, meat broth and a number of other foods as a racemic mixture. The structure of (+)-(J )-furaneol responsible for the characteristic odour is given in formula 8-160. The odour of furaneol is sugary, jammy and reminiscent of strawberries and, at higher concentrations, caramel (threshold concentration is... 

Toluene dioxygenase P. putida El p-Xylene ds-l,2-Dihydroxy-3,6-dimethyl-3,5- Strawberry furanone [53]... 

A flavor is tried at several different levels and in different mediums until the most characteristic one is selected. This is important because the character of a material is known to change quaUty with concentration and environment. For example, anethole, ben2aldehyde, and citral taste different with and without acid. Gamma-decalactone has different characters at different levels of use. -/ fZ-Butyl phenylacetate with acid is strawberry or fmity without acid it is creamy milk chocolate. 2,5-Dimethyl-4-hydroxy-3-(2Fi)-furanone with acid is strawberry without acid it is caramel or meat. 

The berry or the small fruits consist of strawberry, raspberry, blackberry, black currant, blueberry, cranberry and elderberry. The volatiles responsible for the flavour of small fruits are esters, alcohols, ketones, aldehydes, terpenoids, furanones and sulfur compounds (Table 7.3, Figs. 7.1-7.7). As fruit ripen, the concentration of aroma volatiles rapidly increases, closely following pigment formation [43]. 

Sugars, acids and aroma compounds contribute to the characteristic strawberry flavour [85]. Over 360 different volatile compounds have been identified in strawberry fruit [35]. Strawberry aroma is composed predominately of esters (25-90% of the total volatile mass in ripe strawberry fruit) with alcohols, ketones, lactones and aldehydes being present in smaller quantities [85]. Esters provide a fruity and floral characteristic to the aroma [35,86], but aldehydes and furanones also contribute to the strawberry aroma [85, 87]. Terpenoids and sulfur compounds may also have a significant impact on the characteristic strawberry fruit aroma although they normally only make up a small portion of the strawberry volatile compounds [88, 89]. Sulfur compounds, e.g. methanethiol. 

Nozaki et al. [23] characterised the production of (+)-mesifuran [2,5-di-methyl-4-methoxy-3(2H)-furanone], an important flavour compound in arctic bramble, but which also occurs in strawberry and pineapple. After lipase-catalysed (Candida antarctica) enantioface-differentiating hydrolysis of the enol acetate, the pure optically active (+)-mesifuran could be obtained. 

Furanones have been prepared by treatment of y-ketoacids with acetic anhydride. Furanones have also been formed by hydrolysis and dehydrobromination of j8,y-dibromoacids (B-50MI31200). The furan-3(2//)-one system (164) has been prepared by intramolecular cyclization of the diazoketones (163) (74TL3073). Some natural 3(2//)-furanones are known furaneol (166), occurring in strawberries and pineapples, is obtained by acid or base treatment of the dihydroxydiketone (165) (73JOC123). 

Only a few natural 3(2H)-furanones have been found. Furaneol (166) is present in strawberries and pineapples (73JOC123). 

A number of solvents have been used to extract volatiles for aroma analysis but the optimum choice depends on a compromise. Table Gl.1.2 lists the most common solvents used to extract odorants from foods. Although pentane and ethyl acetate are flammable, they have a very low toxicity, represent extremes in polarity, and a sequential extraction using these two solvents will remove most of the volatile odorants from aqueous samples (see Basic Protocol 2) however, if the desire is to do a simpler one-step extraction, then a solvent should be chosen with a polarity that will extract the volatiles of interest. For example, maltol is not extracted well with pentane, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone, the smell of strawberry, is almost insoluble therefore, the choice of the optimum solvent depends on the analyte and may require some testing to find. 

Figure 10.1 Analysis of racemic 2,5-dimethyl-4-hydroxy-3[2H]-furanone (1) obtained from a strawberry tea, flavoured with the synthetic racemate of 1 (natural component), using an MDGC procedure (a) dichloromethane extract of the flavoured strawberry tea, analysed on a Carbowax 20M pre-column (60 m, 0.32 mm i.d., 0.25 pan film thickness carrier gas H2, 1.95 bar 170 °C isothermal) (b) chirospecific analysis of (1) from the strawberry tea extract, transferred for stereoanalysis by using a permethylated /1-cyclodextrin column (47 m X 0.23 mm i.d. carrier gas H2, 1.70 bar 110°C isothermal). Reprinted from Journal of High Resolution Chromatography, 13, A. Mosandl et al., Stereoisomeric flavor compounds. XLIV enantioselective analysis of some important flavor molecules , pp. 660-662, 1990, with permission from Wiley-VCH.

From the wine aromas of Pollux, Castor, and Riesling grapes, Rapp et al. and Schreier and Paroschy have isolated an undesirable strawberry aroma by GC-MS (80V13, 81MI112). This lactone was characterized as 2,5-dimethyl-4-hydroxy-2,3-dihydro-3-furanone 8 ("furaneol") having an odor threshold of 50-100 ppb. 

H)-furanone Lycopsersicon esculentum (Solanaceae) [fruit], in strawberry home-... 

Furaneol is formed when the sugar rhamnose is heated in the presence of a substance containing an amino group through a Maillard reaction (Fig. 3.62). HMF results from heating of fructose (Fig. 3.63). Both furanones occur in various foods. For example, Furaneol has been identified in pineapple, strawberries and popcorn both Furaneol and HMF have been found in meat broth [21 [. Both furanones are applied as flavour modifiers in foods where maltol and ethyl maltol are used [1[. 

Cyclopentenolones with a planar vicinal enol-oxo configuration are known to be powerful aroma active substances with distinct caramel notes. By methylation of the enolic function, this flavour impression is changed drastically to a sweet, mildew, and mouldy odour in the case of 2,5-dimethyl-4-methoxy-3-[2H]-furanone (2). This so-called mesifurane as well as pineapple ketone (1) were stereodifferentiated with modified cyclodextrin [103], Although (1) and (2) can be stereoanalyzed without any racemization, both compounds were detected in strawberries, pineapples, grapes and wines as racemates (Fig. 6.43). 

Fig, 6,43 Stereodifferentiation of 2,5-dimethyl-4-hydroxy-3[2H]-furanone (1) and its methyl-ether (2) from strawberries (A) and pineapples (B). Al/Bl HPLC-chromatogram of raw extracts. A2/B2 enantio-cGC analysis of fractions I, II from raw extracts (from ref [62])... 

Roscher, R., Bringmann, G., Schreier, R, and Schwab, W. 1998. Radiotracer studies on the formation of 4-hydroxy-2,5-dimethyl-3(2//)-furanone in detached ripening strawberry fruits. J. Agric. Food Chem. 46 1488-93. 

Compounds considered to have only minor roles in. saffron aroma [tog.(FD factor.s) < I ] were described as sour, dark chocolate (unknown, no. 1), buttery, cream cheese 2,3 butanedione, no. 3), plastic water bottle (unbiown. no. 4), vinegar, acidic (acelic acid, no. 11), stale, soapy (utiknown, no. 42), fruity, stale (unknown, no. 50) and cotton candy, strawberries [4-hydroxy-2,5-dimeihyl-3(2//)-furanone, no. 59], With its low threshold compound no. 59 is an important component of several foods (ISJ ). 

Low concentrations of ethyl-2-and 3-mercapto-propionate, mentioned earlier in this chapter, have a fruity aroma, whereas in larger quantities they have sulfurous smells. Acree et al. (1990) also demonstrated the presence of 2-amino-acetophenone in Vitis labrusca, as well as two furanones (4-hydroxy-2,5-dimethyl-3-furanone, commonly known as furaneol, and 4-methoxy-2,5-dimethyl-3-furanone) reminiscent of strawberries (Rapp et al., 1980). Most of these compounds have also been identified in Vitis vinifera wines, but at lower concentrations (Guedes de Pinho, 1994 Moio and Etievant 1995). 

In addition to terpenes, carbohydrates serve as a precursor of furanones in plants. The formation of 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF) is an example. This compound, and various forms thereof, are key to the aroma of strawberry. Several researchers have studied the biochemical pathways responsible for the formation of this compound [34,35]. The pathway presented in Figure 4.10 illustrates DMHF formation from its key precursor, 6-deoxy-D-fructose. 

Raab, T., et al. (2006) FaQR, required for the biosynthesis of the strawberry flavor compound 4-hydroxy-2,5-dimethyl-3(2H)-furanone, encodes an enone oxidoreductase. Plant Cell 18,1023-1037... 

The compound 4-hydroxy-2,5-dimethyl-3(2H)-furanone (furaneol, I in Formula 4.67) is the corresponding degradation product from the 6-deoxy-L-mannose (rhamnose) (Formula 4.69). Furaneol can also be formed from hexose phosphates under reducing conditions (cf. 4.2.4.4.6) and from C-3 fragments (cf. Formula 4.47). With a relatively low odor threshold value, furaneol has an intensive caramel-hke odor. It is interesting that furaneol is also biosynthesized in plants, e. g., in strawberries (cf. 18.1.2.6.9) and pineapples (cf. 18.1.2.6.10). 

Strawberry note 4-Hydroxy-2,5-dimethyl-3 (2H)-furanone (HD3F) >1500 pg/1 Characteristic of the cultivar... 

An example of a furanone with methylated hydroxyl in position C-4 is 4-methoxy-2,5-dimethyl-2H-furan-3-one, also known as mesifurane, which is derived from furaneol. (-F)-(R)-Mesifurane (8-163) has a burnt and caramel-Hke odour, but is more subtle and mellow than the odour of furaneol. Mesifurane accompanies furaneol in fruits (such as pineapple, raspberry, strawberry and grape) and other foods. 2,5-Dimethyl-2H-fiiran-3-one, which does not contain the C-4 hydroxy group occurs as a constituent of bread and coffee flavour its odour resembles bread. 

Nowadays, more than 400 compounds forming the large-fruited strawberry Fragaria ananassa and other hybrids, Rosaceae) flavour are known, yet the importance of many of them is not yet fuhy understood. Besides a number of esters (mainly butanoates) and aldehydes, such as (Z)-hex-3-enal, which generally have green and fruity flavours, 4-hydroxy-2,5-dimethyl-2 f-furan-3-one (furaneol, also known as strawberry or pineapple furanone) and its methyl ether 4-methoxy-2,5-dimethyl-2 f-furan-3-one... 

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