Formation of complex natural flavours by biotransformation of apple pomace with basidiomycetes.

Altogether 30 different basidiomycetes were grown submerged in liquid culture media using seven different by-products of the food industry as the only carbon source. Seven fungus/substrate combinations revealed interesting flavour profiles. Culture supernatants of Tyromyces chioneus grown on apple pomace were extracted, and the aroma compounds were analysed by gas chromatography-olfactometry (GC-O). Potent odorants were identified by aroma extract dilution analysis (AEDA), calculation of the odour activity values (OAV), and proven by confection of an aroma model. 3-Phenylpropanal, 3-phenyl-1-propanol, and benzyl alcohol were identified as potent aroma biotransformation products. Headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) experiments showed that 3-phenylpropanal, 3-phenyl-1-propanol, benzyl alcohol, methyl 3-phenylpropionate, methyl 2-phenylacetate, cinnamaldehyde and methyl cinnamate were produced during the cultivation period of eight days. By means of labelling experiments, (E)-cinnamic acid was identified as the precursor of 3-phenylpropanal and 3-phenyl-1-propanol. Basidiomycetes were able to biotransform food by-products to pleasant complex flavour mixtures.