In France, the consumption of spirulina is booming and is favourably received by the consumer due to its nutritional qualities (low in calories, antioxidant properties, rich in iron and vitamins). Its high protein content (60 to 70% of the dry matter) also makes it a product that is popular as an alternative source of proteins to meat and/or soya products. However, its use as an ingredient is having difficulty developing due to its specific organoleptic characteristics (smell, taste, colour). We do however note the heterogeneity of products on the market with significant variations in smell and taste, and flavour notes that are sometimes perceived negatively: hay/mud/‘fish food’. Farming methods can play a role in terms of the organoleptic quality of spirulina, as can stabilisation processes such as drying. However, there are currently no specific characterization tools for spirulina-based products.
The SPIGOU project’s aim was to develop a spirulina characterisation tool from the perspective of organoleptic properties and the characterisation of aromatic molecules. This project funded by the Carnot AgriFood Transition institute was carried out in collaboration between CEVA (Algae Technology and Innovation Centre), ENSCR (Ecole Nationale Supérieur de Chimie de Rennes) and Vegenov.
A tasting jury was trained by Vegenov and enabled a list of descriptors to be established:
- 8 smell descriptors: from hay/ammoniac to toasted bread and green/grass notes
- 6 aroma descriptors: flour/earth, mushroom, seaweed, sesame, smoked, green notes
- 4 flavour descriptors: salty, bitter, umami, astringent
The ENSCR identified 67 volatile compounds (VOCs) in the commercial spirulina samples. Only twenty compounds were selected based on their occurrence in the 28 samples analysed. Overall, acetic acid (AA), ethanol and methanol were the most present molecules in terms of quantities, with strong variability observed between the different samples, for different molecules.
Once the analytical tools were developed (trained jury, analysis and characterisation of volatile compounds) an analysis was carried out on commercial samples as well as on biomasses of fresh (frozen) and dried spirulina produced under different conditions by CEVA.
Without going into details of all the results obtained, we can draw a few general conclusions.
Drying has a notable impact on the smell more than on the aroma. In this way, the VOC content is higher when the spirulina is in dried, powder or compressed form. Only the iodine smell is weaker in dry samples.
When spray-drying, alcohol and ketones are predominantly released. When drying at low temperature, acetic acid is mostly released instead.
The correlations established in the volatile compounds and smells detected by the jury in the sensory analysis emphasise the complex character of smells linked to several molecules. Even if the stabilisation process has little impact on the taste, the mushroom note is more intense in frozen biomasses (in comparison to dried biomasses). Finally, there seems to be an impact of the nitrogen source on the smell, essentially with certain more marked descriptors in the presence of nitrate (Iodic and Maki seaweed) or urea (Tart).
To conclude, the results obtained confirm the complexity of spirulina’s smell. The perception of the smell is sometimes very complex with different perception thresholds from one compound to another, which are also variable between individuals, a matrix effect that is difficult to grasp, and synergy and masking effects between compounds. This complexity justifies the implementation of complementary sensory and chemometric tools within the framework of this project, which may be used in future work.