Flavor-boosting of Phaeodactylum tricornutum by fermentation with edible mushrooms

Microalgae are a promising and sustainable source of nutritious food, especially for use in alternatives to fish and seafood. Among them, Phaeodactylum tricornutum (PT) stands out for its potential to revolutionize future diets with its rich nutrient profile and eco-friendly cultivation methods. However, its typically fishy and "brackish water" off-odor has been a significant deterrent. Using 13 basidiomycetes as starter cultures, the dynamic changes in the aroma were studied. To better understand the aroma development during fermentation, odor-active compounds were identified using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry-olfactometry. By submerged fermentation lasting 39 and 51 hours with Pleurotus citrinopileatus (PCI) and Pleurotus eryngii (PER), respectively, the unpalatable odor of PT was transformed into savory and seafood-like aromas, while retaining most of the valuable carotenoids (fucoxanthin and β-carotene were retained at 75 % and 90 %) and fatty acids (eicosapentaenoic acid and docosahexaenoic acid were preserved at 80 % of their initial concentrations). Throughout the fermentation process, key odorants responsible for the algae's initial green, grassy, and unpleasant odor were reduced, while compounds responsible for savory and seafood-like fragrances increased. A series of sulfur compounds, such as dimethyl disulfide, were found to be major contributors to the post-fermentation aroma.