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A filamentous fungus, Fusarium poae INRA 45, was grown in two liquid Czapek-type media (a Czapek medium, and a yeast extract plus casaminoacids-enriched Czapek medium). Eight gamma-lactones, i.e., gamma-penta-, gamma-octa-, gamma-nona-, gamma-deca-, and gamma-dodecalactone, (6Z)-gamma- and (6E)-gamma-dodecenolactones, and a di-unsaturated gamma-dodecalactone, were tentatively, or conclusively, identified by capillary gas chromatography (GC) and coupled GC-MS, in the volatile fractions of the cultures. Kinetics of the formation of gamma-dodecalactone, (6Z)-gamma- and (6E)-gamma-dodecenolactones, (three major lactones), and gamma-dodecalactone (a minor lactone) were quantitatively studied by computerized GC integration. Variations of the (R/S) ratios of the lactone enantiomers were quantitatively studied by computerized multidimensional gas chromatography (MDGC) integration. The levels of the lactones were superior in the enriched Czapek-type medium to those of the Czapek medium, but the compositions of these media did not influence significantly the (R/S) ratios of these lactones. Formation of the enantiomers is discussed in terms of metabolism of potential precursors.

gamma-Decalactone (gamma-C10) is known to be highly toxic for the microorganims used for its production. In this work, three techniques were studied in order to overcome this toxicity during a bioconversion process using ricinoleic acid as precursor of the lactone: in situ trapping in oily phases, in porous hydrophobic sorbents and in beta-cyclodextrins. Oily phases added to the media (olive, Miglyol, tributyrin, and paraffin) had a protective effect on Sp. salmonicolor, and they improved the lactone production. beta-cyclodextrins, which have a hydrophobic cavity that can trap molecules such as gamma-C10, have been used to protect the yeasts. The results showed insufficient preservation of cell viability. Some sorbents (activated carbon and polystyrene-based sorbents) were successfully tested during bioconversion. In all cases viability exceeded the reference one. Nevertheless the aroma production was 30% lower than the reference. All of these solutions led to some enhancement of the cell viability during bioconversion of methyl ricinoleate to gamma-C10. For improvement of the lactone production, the oil trapping method seemed to be the best with the experimental conditions tested.

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