Downloaded by UNIV OF TENNESSEE KNOXVILLE on December 20, 2014 | http://pubs.acs.org Publication Date: February 21, 1989 | doi: 10.1021/bk-1989-0388.ch002
Chapter 2
Biosynthesis of Chiral Flavor and Aroma Compounds in Plants and Microorganisms K.-H. Engel, J. Heidlas, W. Albrecht, and R. Tressl Technische Universität Berlin, Fachbereich Lebensmitteltechnologie und Biotechnologie, Fachgebiet Chemish-technische Analyse, Seestr.13, D-1000 Berlin 65, Federal Republic of Germany Capillary gas chromatographic determination of optical purities, investigation of the conversion of potential precursors, and characterization of enzymes catalyzing these reactions were applied to study the biogenesis of chiral volatiles in plants and microorganisms. Major pineapple constituents are present as mixtures of enantiomers. Reductions, chain elongation, and hydration were shown to be involved i n the biosynthesis of hydroxy acid esters and lactones. Reduction of methyl ketones and subsequent enantioselective metabolization by Penicillium citrinum were studied as model reactions to rationalize ratios of enantiomers of secondary alcohols i n natural systems. The formation of optically pure enantiomers of aliphatic secondary alcohols and hydroxy acid esters using oxidoreductases from baker's yeast was demonstrated. The world-wide trend to "natural" flavor and aroma has s i g n i f i c a n t l y increased interest i n biogenetical pathways leading to v o l a t i l e s i n natural systems. For c h i r a l compounds the exploration of p o t e n t i a l biosynthetic routes i s even more important, because chemical syntheses are often d i f f i c u l t and expensive; i n many cases however sensory q u a l i t i e s of enantiomers are different (1-3). In our current studies of c h i r a l v o l a t i l e s i n plant and microbial systems we use different a n a l y t i c a l approaches, (a) C a p i l l a r y gas chromatographic separations of diastereoisomeric derivatives are used to determine the configurations of c h i r a l constituents at trace l e v e l s , (b) Chemic a l l y synthesized (labeled) precursors are added to f r u i t tissues and microorganisms. Their transformation into c h i r a l constituents i s investigated by means of c a p i l l a r y gas chromatography/mass spectrometry; the stereochemical course of these metabolizations i s f o l lowed, (c) Enzymes catalyzing the stereospecific conversion of precursors to c h i r a l compounds are i s o l a t e d and characterized; commerc i a l l y a v a i l a b l e enzymes are investigated as model systems to e l u c i date the stereochemical course of biogenetical pathways. The combinat i o n of these methods revealed some new aspects of the biosynthesis of c h i r a l compounds i n natural systems. c
0097-6156/89/0388-0008$06.00/0 1989 American Chemical Society
In Flavor Chemistry; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
2.
ENGELETAL
Biosynthesis of Chiral Flavor and Aroma Compounds
Downloaded by UNIV OF TENNESSEE KNOXVILLE on December 20, 2014 | http://pubs.acs.org Publication Date: February 21, 1989 | doi: 10.1021/bk-1989-0388.ch002
Naturally Occurring Configurations of Pineapple V o l a t i l e s A d i s t i n c t feature of the spectrum of v o l a t i l e s i s o l a t e d from pineapple (Ananas comosus (L.) Merr.) i s the presence of numerous c h i r a l components: 3- and 5-hydroxy esters, 3-, 4- and 5-acetoxy esters, and f - and 6-lactones are prominent pineapple f l a v o r and aroma constituents (4-7). C a p i l l a r y gas chromatographic separation of diastereoisomeric derivatives of (S)-(+)-
