Enantioselective analysis of methyl-branched alcohols and acids in rhubarb (Rheum rhabarbarum L.) stalks.
The enantiomeric compositions of 2-methylbutanol (1), 4-methylhexanol (2), 2-methylbutanoic acid (3), and 4-methylhexanoic acid (4) present in rhubarb (Rheum rhabarbarum L.) stalks were determined. Enantiodifferentiation was achieved via multidimensional gas chromatography using heptakis(2,3,6-tri-O-ethyl)-beta-cyclodextrin as a chiral stationary phase. For all compounds the enantiomeric ratios were in favor of the (R)-enantiomers. The alcohols (1 and 2) exhibited generally high excesses of the (R)-enantiomers, the ratios varying slightly from batch to batch. For the acid (3) a rather narrow range averaging 65% (R):35% (S) was observed. The procedure applied to isolate the volatiles (vacuum headspace technique, simultaneous distillation--extraction, liquid--liquid extraction) had no significant impact on the enantiomeric ratios. The study describes for the first time a plant used as food material in which 2-methyl-branched volatiles are not nearly exclusively present as (S)-enantiomers. This information enlarges the current regulatory knowledge regarding the classification of these important flavor compounds as "natural" on the basis of their enantiomeric ratios.
Dregus
Márta
M
Lehrstuhl für Allgemeine Lebensmitteltechnologie, Technische Universität München, Am Forum 2, D-85350 Freising-Weihenstephan, Germany.
Schmarr
Hans-Georg
HG
Takahisa
Eisuke
E
Engel
Karl-Heinz
KH
D002087:Butyrates / Q000032:analysis* / Q000737:chemistry; D002208:Caproates / Q000032:analysis* / Q000737:chemistry; D002849:Chromatography, Gas; D000441:Hexanols / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D009812:Odorants / Q000032:analysis; D000439:Pentanols / Q000032:analysis* / Q000737:chemistry; D012250:Rheum / Q000737:chemistry*; D012903:Smell; D013237:Stereoisomerism; D014835:Volatilization
D002087:Butyrates; D002208:Caproates; D000441:Hexanols; D000439:Pentanols; C083378:4-methylhexanoic acid; C019475:2-methylbutanoic acid