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...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 2003-11, Vol.51 (24), p.7086-7091
Main Authors: Dregus, Márta, Schmarr, Hans-Georg, Takahisa, Eisuke, Engel, Karl-Heinz
Format: Article
Language:English
Subjects:
alcohols
Biological and medical sciences
Butyrates - analysis
Butyrates - chemistry
Caproates - analysis
Caproates - chemistry
Chromatography, Gas
enantiomers
Food industries
Fruit and vegetable industries
Fundamental and applied biological sciences. Psychology
Hexanols - analysis
Hexanols - chemistry
Humans
Odorants - analysis
odors
organic acids and salts
Pentanols - analysis
Pentanols - chemistry
Rheum - chemistry
Rheum hybridum
Rheum rhabarbarum
rhubarb
Smell
stems
Stereoisomerism
volatile compounds
Volatilization
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Summary: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)-β-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. Keywords: Rhubarb; methyl-branched compounds; chirospecific analysis; MDGC
ISSN:0021-8561
1520-5118
DOI:10.1021/jf030466b