Submerged cultures
of the basidiomycota Cystostereum murrayi emit an
intensive coconut-like, sweetish, and buttery smell. For
identification of the key aroma compounds, an aroma dilution analysis
using dynamic headspace was performed by adjusting the split ratio
of the GC inlet system. Flavor dilution (FD) factors varied from 22 up to ≥218, whereby the largest class of
compounds represented terpenoids, including two rare stereoisomers
of 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether, ee
≥ 99.9). By means of nuclear magnetic resonance spectroscopy,
the substances with the highest FD factors (29, 212, and 218) were identified as diastereomers of 3,6-dimethyl-3a,4,5,6,7,7a-hexayhydro-3H-1-benzofuran-2-one (dihydromenthofurolactone) and as its
corresponding C3-unsaturated lactone. The latter two compounds have
not been described for Cystostereum murrayi or for
any other basidiomycota previously. Supplementation studies using
2-13C-d-glucose indicated that these lactones
as well as the two stereoisomers of dill ether and other terpenoids
were formed de novo by the fungus.
Basidiomycota are
natural sources of aroma compounds.
When grown
in submerged cultures, the fungus Laetiporus montanus (LMO) forms a spicy and meat-like aroma. It thus represents an interesting
candidate for the production of natural savory flavors. To identify
the key aroma compounds of LMO grown submerged in malt extract peptone
medium, the volatiles were isolated by means of automated solvent
assisted flavor evaporation (aSAFE). An aroma extract dilution analysis
was performed by means of gas chromatography-olfactometry coupled
with a flame ionization detector (GC-FID-O). In the aSAFE extract
of LMO, 24 aroma-active compounds were detected. 5-Butyl-2(5H)-furanone (FD 4096), perceived as coconut-like, was determined
as the compound with the highest FD factor. (E,E)-2,4-Decadienal,
(E,Z)-2,4-decadienal, and sotolon were identified
as responsible key compounds for the spicy odor of the submerged cultures.
Moreover, supplementation of the cultures of LMO, Laetiporus
sulphureus, and Laetiporus persicinus with 13C-labeled thiamine hydrochloride resulted in the
formation of 2-methyl-3-(methylthio)furan (MMTF), a compound with
a pronounced meaty flavor. The concentrations of MMTF were further
increased to 19–27 μg L–1 by additional
supplementation of the cultures with ascorbic acid. The results of
this study indicate potential for the biotechnological production
of a meat-like flavor by Laetiporus species.
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