A promising microalga for the production of proteins with high nutritional qualities, Galdieria sulfuraria, is also characterized by the presence of C-phycocyanin, a protein with a characteristic blue pigment. Its cultivation is also being studied as part of the research project ProFuture, in Horizon 2020. (1)
Microalgae are one of the most precious sources of protein and Omega 3 fatty acids, fibers and micronutrients of vegetable origin to contribute to the needs of food safety e nutrition security. In addition to giving natural color to foods (food colouring). In addition to essential ecosystem services, such as CO2 sequestration (2) and bioremediation.
1) Galdieria sulfuraria. Introduction
Galdieria sulfuraria is a polyextremophilic microalga, able to survive in extreme acidity conditions (pH up to 0,2 and optimum of 2), temperature (up to 56-57 °C) and osmotic pressure (up to 400 g/L of sugars and about 180 g/L of salt). It is also able to synthesize:
– C-phycocyanin, a phycobiliprotein known to impart the azure-blue color to the cyanobacterium Spirulina (Arthrospira platensis), (one)
– vitamin E and glycerol.
Its use as food it is not yet authorized in the EU, as we have seen, pending an EFSA opinion expected on 28.3.23. (4) It is already being used in the meantime to produce biofuels and bioremediation works. (5)
su Galdieria sulfuraria progresses, also in Italy, thanks to the strain of G. sulfuraria ACUF (Algae Collection University Frederick II) 064 made available by the Algae Biology laboratory of the Biology Department of the Federico II University of Naples, under the responsibility of Prof. Antonino Pollio. Where a collection of over 800 microorganisms being studied for research and industrial purposes is kept. (6)
The main objectives of research pertain to the optimization of biomass production and the extraction of nutritional and functional substances, such as the same C-phycocyanins, already compared with spirulina to evaluate its production in terms of quantity and quality (e.g. stability).
3) Cultivation methods
mixotropism, i.e. the combination of photosynthesis and the use of carbon-based metabolites (e.g. sugars), is the test condition of Galdieria sulfuraria so far it has been found to be more efficient – compared to autotrophism (which instead only allows the carrying out of photosynthetic activity) – to optimize the production of biomass and bioactive components.
Cultivation it was carried out using a chemostat, to keep production constant over time, after having set the main operating parameters (e.g. substrate to be supplied and to be removed, light, temperature, gas). The system was also effective with high biomass concentrations (> 4 g/L), without undergoing photoinhibition (to which it is generally sensitive) at a concentration of 8 g/L.
The returns of conversion between carbon sources and biomass were very satisfactory, with values up to 89%, therefore only 11% of loss in the form of CO2. Thanks to mixotrophy, it is possible to balance O2 and CO2. To produce biomass without the need for aeration, so as to increase yields and yields as well as reduce production costs.
3.1) Availability of essential amino acids
The amino acids present in Galdieria sulfuraria the two cultivation methods were compared, without observing substantial differences in quantitative terms. Glutamate, aspartate and leucine are the most abundant amino acids, tryptophan, cysteine and histidine the limiting ones. And the presence of taurine, characteristic of animal tissues, is peculiar.
The protein concentration is very high, hovering between 63-65%. With a potential problem that deserves further research regarding the potential limits of bioavailability of these proteins linked to the rigidity of the cell wall, as can occur in the case of fungi. (7)
The profile of essential amino acids di Galdieria sulfuraria was compared with spirulina e Chlorella – two of the main microalgae studied in ProFuture – and soy, the main protein source of vegetable origin. G. sulfuraria demonstrated the best amino acid profile, capable of satisfying the requirement calculated by the FAO, followed by soy and the two microalgae.
3.2) Production of C-phycocyanin
The mixotrophic production di Galdieria sulfuraria allowed to obtain one of the highest yields of C-phycocyanin (10% w/w), although the difference with the autotrophic production was not significant. The yield is instead much lower (< 3% w/w) in heterotrophic conditions (through the sole use of carbon sources).
The extract di Galdieria sulfuraria it resists up to a pH of 3 and a temperature of 55 °C. Spirulina, which also contains C-phycocyanin, loses much of its chromatic intensity at higher pH conditions, as well as already at 45 °C. Galdieria sulfuraria it can therefore be used in the formulation of acidic foods (e.g. fruit juices, jams) and other foods that contain them, as well as in those subject to heat treatments (e.g. pasteurization).
4) novel food, food colouring, food additive?
The extracts obtained from food sources can be qualified in the EU as coloring foods, i.e. as food ingredients, when a number of conditions are met. In essence, when the primary extract maintains similar characteristics (in the balance between pigments, nutritional or flavoring constituents) to those of the raw material. In the different case of selective extraction, with a high concentration of pigments, the extracts qualify instead as food additives and are subject, in the EU, to a specific authorization procedure. (8)
G. sulfuraria it must first be authorized as novel food, for its use (also in the form of extract) as a food ingredient, pursuant to reg. EU 2015/2283. spirulina (Arthrospira platensis), instead considered as 'not novel', can already be used in the EU without particular restrictions. And its aqueous extract with phycocyanobiliproteins has also been approved in France as a traditional food ingredient (9,10).
5) Provisional conclusions
The extensive equipment of protein veg, essential amino acids (including taurine) and the characteristic blue pigment indicate Galdieria sulfuraria as a very promising microalgae for use in the food sector.
It awaits confidently your authorization as novel food in the EU to make the most of this potential, also in view of its use in innovative food products inspired by phycogastronomy, in the combination of health and taste. (11)
Dario Dongo and Andrea Adelmo Della Penna
Footnotes to the story
(1) Dario Dongo. ProFuture, microalgae to feed the planet. The EU research project. GIFT (Great Italian Food Trade). 18.6.19
(2) Prasad,R.;Gupta,SK; Shabnam, N.; Oliveira, CYB; Nema, AK; Ansari, FA; Bux, F. (2021). Role of Microalgae in Global CO2 Sequestration: Physiological Mechanism, Recent Development, Challenges, and Future Prospective. Sustainability 2021, 13, 13061. https://doi.org/10.3390/su132313061
(3) Abuses et al. (2022). Mixotrophic cultivation of Galdieria sulphuraria for C-phycocyanin and protein production. AlgalResearch 61: 102603, https://doi.org/10.1016/j.algal.2021.102603
(4) Dario Dongo, Giulia Torre. Microalgae for food use and regulation of Novel Foods, the state of the art in the EU. GIFT (Great Italian Food Trade). 29.1.22
(5) Perez Saura et al. (2022). Cell adaptation of the extremophilic red microalga Galdieria sulphuraria to the availability of carbon sources. Front. Plant Sci. 15: 978246, https://doi.org/10.3389/fpls.2022.978246
(6) See http://www.dipartimentodibiologia.unina.it/laboratoriobiologiaalghe/
(7) Dario Dongo, Andrea Adelmo Della Penna. Vegetable alternatives to meat, the nutritional challenges. GIFT (Great Italian Food Trade). 19.12.22
(8) Dario Dongo, Andrea Adelmo Della Penna. Coloring foods and their extracts. Ingredients or additives? GIFT (Great Italian Food Trade). 24.12.22
(9) Conseil Superieur D'Hygiene Publique De France. Rapport approved by the working group 'Aliments non traditionnels'. 30.9.86/XNUMX/XNUMX
(10) The use of the aqueous extract of Spirulina is authorized in France, but is not reported in the Novel Food Catalog. Therefore, to find out if its use is also allowed in the rest of Europe, it is necessary to send a request for consultation to the European Commission, according to the procedures set out in the reg. EU 2018/456
(11) Dario Dongo, Andrea Adelmo Della Penna. Algae and microalgae for food use in Europe, the ABC. GIFT (Great Italian Food Trade). 14.11.22/XNUMX/XNUMX