Volatiles responsible for the seasoning‐like flavour of cell cultures of Laetiporus sulphureus

Abstract

The basidiomycete Laetiporus sulphureus (the edible 'chicken mushroom') imparted a strong seasoning odour when grown on a substrate containing wheat gluten as the sole carbon and nitrogen source. Secreted fungal peptidases hydrolysed the gluten substrate, and numerous potent heterocyclic flavours, among them sotolon (3-hydroxy-4,5-dimethyl-5H-furan-2-one) and other furanones, emerged in the liquefying hydrolysate. The fungal cells were supplemented with presumed precursors of sotolon, such as acetaldehyde, α-ketobutanoic acid, α-oxopentandioic acid, L-glutamic acid, L-isoleucine, and L-(+)-ascorbic acid. Upon addition of isoleucine and ferrous iron the formation of sotolon became measurable within 2 days. Small amounts of 4-hydroxyisoleucine (HIL) were identified in the culture supernatant of L. sulphureus by HPLC-FD and LC-SIM-MS/MS. An enzymatic formation of sotolon via a presumed isoleucine hydroxylase could not be excluded; however, balancing biochemical vs. chemical pathways, a slow chemical hydroxylation of the isoleucine released during the enzymatic hydrolysis of gluten seemed much more likely because ferric iron was present in the culture medium.

Formation of a Meat-Like Flavor by Submerged Cultivated Laetiporus montanus

“…■ RESULTS AND DISCUSSION AEDA of Submerged Cultures of LMO. While some studies on the aroma compound profile of LSU have already been published, 10,11,15,16 no data have been available for LMO so far. When grown submerged in MEP, LMO, and LSU formed similar orange colored mycelia, the mycelia of LMO become slightly more intensely colored than those of LSU (data not shown).…”

“…Two diastereomers of 4,5-dimethyldihydrofuran-2(3H)-one have been tentatively identified and olfactorily perceived, and it cannot be excluded that the respective odors are emitted by enantiomeric pairs, since the enantiomeric pairs such as (4S,5S)-dimethyldihydro-2(3H)-furanone and (4R,5R)-dimethyldihydro-2(3H)-furanone or (4S,5R)-dimethyldihydro-2(3H)-furanone and (4R,5S)-dimethyldihydro-2(3H)-furanone cannot be separated by means of nonchiral analysis. 4,5-Dimethyldihydro-2(3H)-furanone was also tentatively identified in submerged cultures of LSU by Krings et al 10 Many of the other heterocyclic compounds detected by Krings et al 10 in the submerged cultures of LSU were not perceived as aroma compounds in LMO. Methional, acetic acid, methyl 2furanoate, 2-furanmethanol, 3-methylbutanoic acid, benzothiazole, methyl 3-furoate, furaneol, 2,6-dimethoxyphenol, benzeneacetic acid, and 2-(methylmercapto)benzothiazole (compounds not listed in table 1) were detected in the analyzed MEP control without fungi with the same or higher FD factors and were therefore attributed to the aroma of the culture medium.…”

Isotope labelling experiments on the formation pathway of 3‐hydroxy‐4,5‐dimethyl‐2(5H)‐furanone from l‐isoleucine in cultures of Laetiporus sulphureus

“…[12] In brief, a Varian HPLC 212-LC coupled to a 320-MS Triple Quad LC-MS 2 was used in the ESI-positive mode: capillary, 30 V; needle voltage, 5000 V; nebulizer gas, 379 kPa at 50°C; drying gas, 124 kPa at 200°C; and argon at 200 mPa and 15 V collision energy. [12] In brief, a Varian HPLC 212-LC coupled to a 320-MS Triple Quad LC-MS 2 was used in the ESI-positive mode: capillary, 30 V; needle voltage, 5000 V; nebulizer gas, 379 kPa at 50°C; drying gas, 124 kPa at 200°C; and argon at 200 mPa and 15 V collision energy.…”

“…[12] While the precursor feedings suggested a bioconversion of L-isoleucine while maintaining the C6-carbon backbone, alternative routes to sotolon, such as the aldolization of 2-oxobutanonic acid and acetaldehyde as in wine, [5,16] or the formation from Maillard products, such as butane-2,3-dione and 2-hydroxyacetaldehyde [17] could not be ruled out in the fungal culture until now. Quantitative formation of sotolon and degradation of L-isoleucine did not correlate well.…”

“…In wine and sake, degradation products of L-threonine resulted in the formation of sotolon, [5] whereas ascorbic acid and ethanol were found to be the precursors in citrus soft drinks. [12] Therefore, a biogenesis of sotolon via bioconversion of L-isoleucine was assumed. [7][8][9] In fenugreek seeds, the lactone originated from a rather uncommon metabolite of L-isoleucine, L-4-hydroxyisoleucine, which spontaneously formed sotolon through thermal deamination.…”