Production of natural flavour compounds using side-streams of the Citrus processing industries by monokaryotic strains of Pleurotus sapidus

BÜRGER F.; OMARINI A.; KRAHE N-K.; FRAATZ M.A.; BERGER R.G.; ZORN H.

Eisenach

Simposio; 2th Wartburg Symposium on Flavor Chemistry & Biology; 2019

Wartburg Stiftung Eisenach

According to the economic concept of reduce, reuse, and recycle, citrus side-streams represent a raw material rich in precursors for the transformation to value-added compounds and their industrial application. Citrus side-streams contain comparatively high amounts of monoterpenes, including (R)-limonene and beta-myrcene. Basidiomycetes are able to transform these terpenes into highly sought-after aroma compounds. For example, beta-myrcene was biotransformed by Pleurotus sapidus, a close relative of the oyster mushroom P. ostreatus, to the woody, citrus-like smelling perillene. Due to their high genetic variability, especially monokaryotic strains of this fungus seem to be predestinated for the application as non-GMO biocatalysts. An additional advantage of the monokaryons haploid stage is the avoidance of unforeseeable gene interactions between two nuclei. In the present study, citrus side-streams were used as the main carbon source for the cultivation of monokaryotic strains of P. sapidus. After a screening of over 60 monokaryotic strains, those responsible for pleasant odours reminiscent of woodruff, herbs, and sweetish notes, were chosen for further investigation. The volatiles of the supernatants were extracted by headspace solid phase microextraction and stir bar sorptive extraction, respectively. Additionally, liquid-liquid extractions (using pentane/diethyl ether as solvent) of the culture broths followed by solvent assisted flavour evaporation were performed. The extracts were analyzed by means of gas chromatography-mass spectrometry-olfactometry. The dominating flavour compound was identified as p-anisaldehyde. During the cultivation of P. sapidus in standard nutrition solution this compound was also formed, but the fermentation of the citrus side-streams increased the formation of this vanilla and anise-like smelling substance significantly. The fungus was also able to synthesize halogenated aromatic compounds, which will be subject of further studies.