✍ Scribed by Thomas Haffner; Andreas Nordsieck; Roland Tressl
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investigate the biochemical formation of linolenic-acid-derived aroma compounds in cultures of the yeast Sporobolomyces odorus, using an established gas chromatographic/mass spectrometric (GC/MS) method. Three compounds were identified as labeled : (Z)-dec-7-eno-5-lactone (8-jasmin lactone), (Z,Z)-dodeca-6.9-dieno-4-lactone, and (2E,4Z)-hepta-2,4-dienoic acid. Both lactones were biosynthesized mostly under conservation of the initial configuration from their corresponding oxygenated linolenic-acid intermediates. The application of (13S,9Z,1 1E,15Z)-13-hydroxy (9,10,12,13,15,16-zH~)octadeca-9,l 1,15-trienoic acid (D6-7) as a OH-functionalized precursor of 8-jasmin lactone allowed to gain insight into the stereochemical course of the biosynthesis to both enantiomers of this lactone. In this experiment, 88.3 % of the metabolized labeled precursor was transformed under retention of the original configuration of the (R)-enantiomer. This investigation is also a contribution to a better understanding of the C=C bond isomerization steps which took place during thep -oxidative degradation of the substrate.
Introduction. -Chiral y -and 6 -1actones make significant contributions to the sensory properties of many foods. In contrast to their important role in flavor research and industry, the biogenetic pathways to the aroma compounds are often unknown. The chirospecific analysis of y -and 6 -1actones (by means of enantiomer separation by gas chromatography (GC) on chiral capillary columns) is an effective tool to prove the authenticity of natural flavorings in food. Therefore, the knowledge of the biosynthetic pathways to lactone enantiomers is of importance. Recently, the biosynthesis of dodecano-4-lactone in peaches, strawberries, and some other fruits was investigated by using suitable deuterated fatty acid precursors [ 11. Other experiments performed with strawberries demonstrated that (E)-dec-3-enoic acid can serve as a substrate in the biosynthesis of decano-4-actone [2] [3]. However, vegetable systems have some disadvantages, such as the dependency of the corresponding biochemical activity from the season and the degree of fruit ripeness. As appropriate models, lactone-producing microorganisms were successfully used to overcome these restrictions. Aspects of the microbial pathways to decano-5lactone and some y-lactones were studied by using labeled fatty acids or oxygenated fatty acids as precursors [3-lo]. The dominant pathway to (R)-decano-4-lactone in the yeast Sporobolomyces odorus was characterized as a (R)-12-hydroxylation of oleic acid ( = (2)octadec-9-enoic acid) followed by B -oxidation. In this study, oleic acid was also transformed into linoleic acid ( = (Z,Z)-octadeca-9,12-dienoic acid; l), which subsequently was degraded to (Z)-dodec-6-eno-4-lactone (2), possessing an enantiomer ratio ( R ) / ( S ) of 92: 8 (see Scheme I). The biosynthesis of (R)-decano-5-lactone (3; (R) > 99%) in S.odoru.7 is initiated by a lipoxygenation at C(13) of linoleic acid (1). It could be shown
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