Abstract
A novel alcohol-free beverage with a fruity, slightly sour, sweetish, fresh, and plum-like flavor was produced by incorporating the edible mushroom shiitake (Lentinula edodes) into the fermentation process. Shiitake pellets were used as a biocatalyst to promote the synthesis of the fruity esters methyl 2-methylbutanoate and 2-phenylethanol from amino acids and an organic acid present in the wort. We investigated the impact of two critical process parameters (volumetric power input and inoculum concentration) on the morphology of, and flavor production by, the shiitake pellets in a 1 L stirred bioreactor. Increasing the volumetric power input and biomass concentration influenced the morphology of the pellets and promoted the production of the most important flavor compound methyl 2-methylbutanoate in the beverage. Furthermore the worty off-flavor methional was degraded during the cultivation in stirred bioreactor by shiitake pellets. These findings provide useful information to facilitate the scale-up of the biotransformation and fermentation process in bioreactors.
Highlights
The submerged cultivation of basidiomycetes, such as the shiitake mushroom (Lentinula edodes), allows the production of valuable secondary metabolites, including pharmaceuticals, enzymes, and natural flavor compounds [1,2,3]
The complex morphology of these organisms makes the cultivation process challenging, because the submerged fungi can grow as viscous mycelia, or as dense pellets depending on process
We investigated the impact of inoculum size, and volumetric power input under different agitation rates, on the morphology of shiitake pellets in the wort, and the quantities of key flavor compounds produced during cultivation
Summary
The submerged cultivation of basidiomycetes, such as the shiitake mushroom (Lentinula edodes), allows the production of valuable secondary metabolites, including pharmaceuticals, enzymes, and natural flavor compounds [1,2,3]. The volumetric power input is one of the critical process parameters in the submerged cultivation of shear-sensitive organisms such as basidiomycetes. This process parameter can be regulated by agitation and aeration intensity and by stirrer geometry. Agitation is required for mixing and to achieve adequate oxygen transfer, but excessive agitation subjects the mycelia to mechanical stress and this can influence the production of target metabolites. It is, important to achieve the optimal balance between adequate oxygen supply and minimal mechanical stress [6,7]. The used impeller type is another aspect, which should be considered in the cultivation of shear-sensitive basidiomycetes
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