Raisin volatile components

Raisin and Dried Fig Volatile Components Possible Insect Attractants... 

The vacuum steam volatile oils of both raisins and dried figs have been analyzed by capillary GLC-mass spectrometry. A total of 38 components were Identified In the volatile oil of raisins and 34 components In the volatile oil of dried figs. Major volatile components In both raisins and dried figs Included fatty acid degradation products such as nonanolc and octanolc acids, (E)-2-decenal, (E)-2-octenal and nonanal. Benzaldehyde was an additional major component of dried figs. The most unusual components were 2-hexyl-3-methyl-malelc anhydride and l-octen-3-one In the raisin volatile oil. 

The major compounds In the raisin volatile oil Include the aliphatic acids octanolc, nonanolc, hexanolc, heptanolc, and decanolc acids as well as 2-hexyl-3-methylmalelc anhydride (previously identified by some of the authors, A), nonanal, phenylacetaldehyde and 2-pentylfuran. The most unusual component is 2-hexyl 3-methylmalelc anhydride. Anhydrides are usually hydrolyzed by water and are not likely to occur in foods because most foods have high concentrations of water. Conditions In dried foods are apparently, however, suitable for the stability and possibly the formation of anhydrides. It is surprising that this anhydride survives the vacuum steam distillation Isolation procedure although the relatively low temperature (ca. 50°C) and likely rapid transfer to the hexane solvent are probably favorable. 

Unusual components found In the dried fig volatile oil include 3-phenylpropanal (dlhydrocinnamaldehyde), llnalool oxide A (2-methyl-2-vlnyl-5(2 -hydroxy-2 propyD-tetrahydrofuran), llnalool oxide C (5-hydroxy-2,6,6-trlmethyl-2-vinyltetrahydro-pyran) and N-ethyl-2-formylpyrolle. The last compound was also identified in raisin volatiles but in both foods the identification was only by comparison with a published spectrum ( ) and no authentic sample was available. 

Steam distillation continuous extraction of the raisins under reduced pressure gave a volatile raisin oil which amounted to 5-10 ppm of the raisins. The oil was analyzed by capillary GLC-mass spectrometry (GLC-MS). The analysis was repeated with volatile oils from several different samples of raisins. Figure I shows a GLC analysis of typical oil. The results are listed In Table I. Peak numbers corresponding to the peaks In Figure I are shown In the first column of Table I alongside the compound s name. Some Idea of the approximate relative percentages of the components In a typical oil (calculated from peak areas) Is also listed In Table I. 

The very volatile fermentation components discussed above seem to be largely lost in the dry fig. The major component of the dried fig volatile oil is benzaldehyde. Other major components include the aliphatic acids octanolc and nonanoic acids. These acids were also major components of raisins and have aromas reminiscent of both raisins and dried figs. They had previously also been found as major components of dried almond hulls (7 ) which Is essentially also a dried fruit. The 2-hexy-3-methyl-malelc anhydride common to raisins and dried almond hulls (j4) was not detected in dried figs. 

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