Eight microalgae and five macroalgae were assessed by a trained panel of judges to measure their taste and aroma characteristics. At the same time, analyses of volatile and soluble compounds with a potential impact on taste and smell were carried out. The results were compared with commercial seafood flavours.
Tetraselmis chui, Rhodomonas salina and Phaeodactylum tricornutum have the strongest marine odour and taste notes, with mussel, crab and fish odours as well as an umami and salty taste.
These three microalgae have a crab-like odour and aroma superior to those measured in Palmaria and Ulva. Their mussel odour is equivalent. Tetraselmis chui and Rhodomonas salina had the strongest fishy odour and aroma, while Tetraselmis chui and Phaeodactylum tricornutum had the strongest umami taste. However, they also have a more intense green odour that could be undesirable.
Chlorella vulgaris, Skeletonema costatum and Dunaliella salina have weaker marine scents, making them less interesting candidates. Chlorella vulgaris and Skeletonema costatum have the strongest earthy notes, while Dunaliella salina has a high floral odour which makes its profile atypical. S. costatum also has the bitterest and least sweet taste.
Nannochloropsis oceanica has a fishy, mussel-like odour similar to Rhodomonas salina, a fishy aroma equivalent to T. chui. However, like Tisochrysis lutea, its rancid odour does not make it a good candidate.
Microalgae share a large number of volatile compounds active on odour with seafood aromas such as :
- Fatty acid derivatives : the levels of saturated aldehydes (pentanal, hexanal, heptanal, octanal, decanal), unsaturated aldehydes (4-heptanal (Z) and 2,6-nonadienal (E,E)), unsaturated alcohols (1-octen-3-ol) and unsaturated ketones (3,5-octadien-2-one) are in comparable quantities in Tetraselmis chui, Rhodomonas salina, Phaeodactylum tricornutum and commercial flavourings.
- Volatile compounds: in particular dimethyl sulphide, which is found in crab and mussel flavouring and in the microalgae T. chui, R. salina and P. tricornutum. While it has not been detected in microalgae with weaker sea odours such as D. salina and C. vulgaris, it is found in significant quantities in T. lutea and S. costatum. The odour of dimethyl sulphide is potentially masked by the presence of other aromatic compounds such as fatty acid derivatives and aldehydes. Macroalgae, with the exception of Ulva, contain fewer sulphur compounds overall.
- Volatile nitrogen compounds: trimethylamine, a marker of fish spoilage, contributes to fish and shellfish odours when present in small quantities. Present in seafood aromas, it is found in T. chui, R. salina and P. tricornutum. It is absent in macroalgae.
- Alkyl aldehydes and benzaldehydes: these are found in comparable quantities in fish, crustaceans and molluscs and in the microalgae T. chui, R. salina and P. tricornutum. They are present in smaller quantities in algae, with the exception of Palmaria palmata. The microalgae C. vulgaris, T. lutea and S. costatum contain more compounds with malty/coffee and nutty/almond notes.
Other compounds are present in microalgae and can be described as having atypical odours in relation to the characteristics of the seafood products sought:
- carotenoid derivatives: these contribute to floral and woody notes. They were found in greater quantities in D. salina, which had one of the strongest floral scents.
- Diketones and esters: microalgae have more 2,3-butanedione, a compound with a buttery note, and esters with fruity notes.
Microalgae have similarities with seafood flavours in their profiles of certain free amino acids that contribute to taste: glutamic acid (umami), alanine (sweet) and arginine (bitter/sweet). However, glycine (sweetness), which is found in seafood flavours, is absent (or in quantities below the detection threshold) in microalgae and algae. Microalgae also contain 5′-ribonucleotides that contribute to umami taste above the detection threshold, with the exception of D. salina and N. oceanica. The contribution of salts (Na+ and K+) is similar between the micoralgae Tetraselmis chui, Rhodomonas salina and Phaeodactylum tricornutum and the algae Palmaria palmata and Ulva laetevirens/rigida.
The authors calculated the umami equivalent concentration (EUC) from the amino acid content of 5′-ribonucleotides. D. salina, the least intense in umami, has the lowest EUC, while P. tricornutum and T. chui are among those with the highest EUC and a pronounced umami taste. However, S. costatum and T. lutea have equally high EUCs but with a less pronounced umami taste, which is probably linked to masking by bitterness.
In conclusion, this article identified three promising microalgae among the species examined to serve as plant-based alternatives to animal seafood products: R. salina, T. chui and P. tricornutum. These microalgae share important odour and taste compounds with seafood flavours (dimethyl sulphide (DMS), trimethylamine (TMA) and derived polyunsaturated aldehydes, alcohols and ketones). On the other hand, the presence of a higher bitterness in R. salina and especially in P. tricornutum, and a green note in T. chui, could be undesirable in these alternatives. T. chui and P. tricornutum also have a high umami potential.
Reference: Coleman, B., Van Poucke, C., Dewitte, B., Ruttens, A., Moerdijk-Poortvliet, T., Latsos, C., De Reu, K., Blommaert, L., Duquenne, B., Timmermans, K., Van Houcke, J., Muylaert, K., Robbens, J., 2022. Potential of microalgae as flavoring agents for plant-based seafood alternatives. Future Foods 5, 100139. https://doi.org/10.1016/j.fufo.2022.100139