| Abstract
| - 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 ratioswere in favor of the (R)-enantiomers. The alcohols (1 and 2) exhibited generally high excesses ofthe (R)-enantiomers, the ratios varying slightly from batch to batch. For the acid (3) a rather narrowrange averaging 65% (R):35% (S) was observed. The procedure applied to isolate the volatiles(vacuum headspace technique, simultaneous distillation−extraction, liquid−liquid extraction) had nosignificant impact on the enantiomeric ratios. The study describes for the first time a plant used asfood material in which 2-methyl-branched volatiles are not nearly exclusively present as (S)-enantiomers. This information enlarges the current regulatory knowledge regarding the classificationof these important flavor compounds as “natural” on the basis of their enantiomeric ratios. Keywords: Rhubarb; methyl-branched compounds; chirospecific analysis; MDGC
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