Simultaneous improvement of aroma and bioactivity of Spirulina platensis: A novel approach by Basidiomycota fermentation.

Fermentation has emerged as a promising strategy to modify aroma profile of Spirulina platensis, yet the application of Basidiomycota for aroma improvement remains largely unexplored. In this study, a Basidiomycota-S. platensis fermentation system was established using edible mushroom strains to improve its sensory properties. Among twelve tested strains, Stropharia rugosoannulata showed the most pronounced aroma improvement after 56 h fermentation at 24 °C under shaking conditions. Sensory evaluation indicated that fermentation effectively reduced undesirable fishy and earthy odors and introduced floral, fruity, and sweetish notes. Further aroma profiling attributed these changes to a marked decrease in lipid-derived aldehydes and the formation of fruity ethyl esters. Ethyl 2-methylbutanoate, ethyl 2-methylpropanoate, and ethyl 3-methylbutanoate were identified as key contributors to the fruity aroma. Precursor supplementation experiments suggested that involvement of branched-chain amino acid metabolism in the formation of the fruity ethyl esters via the Ehrlich pathway. In addition to aroma improvement, fermented S. platensis significantly reduced TNF-α-induced COX-2 expression and intracellular reactive oxygen species levels in EA.hy926 cells compared with the unfermented sample. Cytotoxicity assays using HepG2 cells showed no significant cytotoxic effects after fermentation. Overall, this study establishes a novel Basidiomycota-S. platensis fermentation system that improves aroma quality and enhances its anti-inflammatory and antioxidant potential under the present experimental conditions. The findings also provide supporting evidence for the proposed involvement of branched-chain amino acid metabolism in fruity ethyl ester formation and provide a basis for developing aroma-improved microalgal ingredients.