Production of an Anise- and Woodruff-like Aroma by Monokaryotic Strains of Pleurotus sapidus Grown on Citrus Side Streams

A Novel O- and S-Methyltransferase from Pleurotus sapidus Is Involved in Flavor Formation

Increasing consumer aversion to non-natural flavoring substances is prompting a heightened interest in enzymatic processes for flavor production. This includes methylation reactions, which are often performed by using hazardous chemicals. By correlation of aroma profile data and transcriptomic analysis, a novel O-methyltransferase (OMT) catalyzing a respective reaction within the formation of p-anisaldehyde was identified in the mushroom Pleurotus sapidus. Heterologous expression in E. coli followed by purification allowed for further characterization of the enzyme. Besides p-hydroxybenzaldehyde, the proposed precursor of p-anisaldehyde, the enzyme catalyzed the methylation of further hydroxylated aromatic compounds at the meta- and para-position. The Km values determined for p-hydroxybenzaldehyde and S-adenosyl-l-methionine were 80 and 107 μM, respectively. Surprisingly, the studied enzyme enabled the transmethylation of thiol-nucleophiles, as indicated by the formation of 2-methyl-3-(methylthio)furan from 2-methyl-3-furanthiol. Moreover, the enzyme was crystallized at a resolution of 2.0 Å, representing the first published crystal structure of a basidiomycetous OMT.

Mycelium vs. Fruiting Bodies of Edible Fungi-A Comparison of Metabolites

Edible mushrooms are widely appreciated for their appealing flavours, low caloric values and high content of presumably health-protecting metabolites. Their long history of safe use together with the looming worldwide food crisis have revived the idea of generating meat analogues and protein isolates by the controlled fermentation of mycelia of these edible fungi as a dietary option. The occurrence of proteins, polysaccharides, smaller metabolites, metal ions and toxins in mycelia and fruiting bodies is compared among the three most popular species, Agaricus bisporus (button mushroom), Pleurotus ostreatus (oyster mushroom), Lentinus edodes (shiitake) and some closely related species. Large effects of substrate chemistry, strain, developmental stage and ecological interactions result in a wide variation of the concentrations of some metabolites in both mycelial cells and fruiting bodies. This is obviously a result of the high adaptation abilities required to survive in natural habitats. Fungal bioprocesses are decoupled from agricultural production and can be operated anytime, anywhere, and on any scale according to demand. It is concluded that fungal biomass, if produced under food-grade conditions and on an industrial scale, could provide a safe and nutritious meat substitute and protein isolates with a high biological value for future vegan foods.

Improved Foods Using Enzymes from Basidiomycetes

Within the kingdom of fungi, the division Basidiomycota represents more than 30,000 species, some with huge genomes indicating great metabolic potential. The fruiting bodies of many basidiomycetes are appreciated as food (“mushrooms”). Solid-state and submerged cultivation processes have been established for many species. Specifically, xylophilic fungi secrete numerous enzymes but also form smaller metabolites along unique pathways; both groups of compounds may be of interest to the food processing industry. To stimulate further research and not aim at comprehensiveness in the broad field, this review describes some recent progress in fermentation processes and the knowledge of fungal genetics. Processes with potential for food applications based on lipases, esterases, glycosidases, peptidases and oxidoreductases are presented. The formation and degradation of colourants, the degradation of harmful food components, the formation of food ingredients and particularly of volatile and non-volatile flavours serve as examples. In summary, edible basidiomycetes are foods—and catalysts—for food applications and rich donors of genes to construct heterologous cell factories for fermentation processes. Options arise to support the worldwide trend toward greener, more eco-friendly and sustainable processes.