A promising microalga for producing proteins with high nutritional qualities, Galdieria sulphuraria is also characterized by the presence of C-phycocyanin, a protein with a characteristic blue pigment. Its cultivation is also being studied under the ProFuture research project in Horizon 2020. (1)
Microalgae are one of the most valuable sources of protein and omega-3 fatty acids, fiber, and plant-derived micronutrients to contribute to food security and nutrition security needs. As well as to give natural color to foods(coloring food). In addition to essential ecosystem services, such as CO2 (2) sequestration and bioremediation.
1) Galdieria sulphuraria. Introduction
Galdieria sulphuraria
is a polyestremophilic microalga, capable of surviving extreme conditions of acidity (pH down 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 capable of synthesizing:
– C-phycocyanin, a phycobiliprotein known to impart blue-blue color to the cyanobacterium Spirulina(Arthrospira platensis), (3)
– Vitamin E and glycerol.
Its use as a food is not yet authorized in the EU, as noted, pending an EFSA opinion due on 3/28/23. (4) It is already being used to produce biofuels and bioremediation works. (5)
2) Research
Research on Galdieria sulphuraria is progressing, also in Italy, thanks to G. sulphuraria ACUF(Algae Collection University Federico II) strain 064 made available by the Algae Biology Laboratory of the Department of Biology, University Federico II of Naples, under the responsibility of Prof. Antonino Pollio. Where a collection of more than 800 microorganisms being studied for research and industrial purposes is kept. (6)
The main research objectives pertain to the optimization of biomass production and the extraction of nutritional and functional substances, such as the C-phycocyanins themselves, which have already been compared with spirulina to evaluate their production in terms of quantity and quality (e.g., stability).
3) Cultivation methods
Myxotrophism, i.e., the combination of photosynthesis and the use of carbon-based metabolites (e.g., sugars), is the test condition of Galdieria sulphuraria hitherto found to be more efficient-than autotrophism (which instead allows only photosynthetic activity to take place)-in optimizing the production of biomass and bioactive components.
Cultivation was carried out using a chemostat to keep production constant over time, after setting the main operating parameters (e.g., substrate to be supplied and removed, light, temperature, gas). The system was also effective at high biomass concentrations (> 4 g/L), without undergoing photoinhibition (to which it is generally sensitive) at a concentration of 8 g/L.
The conversion efficiencies between carbon sources and biomass were very satisfactory, with values up to 89%, so only 11% loss in the form of CO2. Due to mixotrophy, O2 and CO2 can be balanced. 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
Amino acids in Galdieria sulphuraria were compared between the two cultivation methods, and no substantial differences in quantity were observed. 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 issue that warrants further research regarding the potential limits of bioavailability of such proteins related to cell wall rigidity, as may be the case with fungi. (7)
The essential amino acid profile of Galdieria sulphuraria was compared with Spirulina and Chlorella-two of the main microalgae studied in ProFuture-and soy, the main plant-based protein source. G. sulphuraria showed the best amino acid profile, meeting the requirement calculated by FAO, followed by soybean and the two microalgae.
3.2) Production of C-phycocyanin
Mixotrophic production of Galdieria sulphuraria resulted in one of the highest yields of C-phycocyanin (10% w/w), although the difference with autotrophic production was not significant. In contrast, the yield is much lower (< 3% w/w) under heterotrophic conditions (through the use of carbon sources alone).
Galdieria sulphuraria extract withstands up to a pH of 3 and a temperature of 55 °C. In contrast, that of spirulina, which also contains C-phycocyanin, loses much of its color intensity at higher pH conditions, as well as already at 45 °C. Galdieria sulphuraria can therefore be used in the formulation of acidic foods (e.g., fruit juices, jams) and other foods containing them, as well as in those subject to heat treatment (e.g., pasteurization).
4) Novel food, coloring food, food additive?
Extracts obtained from food matrices can be qualified in the EU as coloring foods, i.e., food ingredients, under a number of conditions. In essence, when the primary extract maintains similar characteristics (in the balance of pigments, nutritional constituents or flavorings) to those of the raw material. In the different case of selective extraction, with a high concentration of pigments, the extracts, on the other hand, qualify as food additives and are subject, in the EU, to a special authorization procedure. (8)
G. sulphuraria
must first be authorized as a novel food, for its use (including in the form of an extract) as a food ingredient, under Reg. EU 2015/2283.
Spirulina
(Arthrospira platensis), on the other hand considered as ‘not novel‘, can already be used in the EU without special restrictions. And its aqueous extract with phycocyanobiliprotein has also been approved in France as a traditional food ingredient (9,10).
5) Interim Conclusions
The ample supply of veg protein, essential amino acids (including taurine) and characteristic blue pigment indicate Galdieria sulphuraria as a very promising microalga for use in the food sector.
Its authorization as a novel food in the EU is confidently awaited in order to make the most of this potential, also with a view to its use in innovative food products inspired by phycogastronomy, in the combination of health and taste. (11)
Dario Dongo and Andrea Adelmo Della Penna
Notes
(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,S.K.; Shabnam, N.; Oliveira, C.Y.B.; Nema, A.K.; Ansari, F.A.; 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) Abiusi et al. (2022). Mixotrophic cultivation of Galdieria sulphuraria for C-phycocyanin and protein production. Algal Research 61:102603, https://doi.org/10.1016/j.algal.2021.102603
(4) Dario Dongo, Giulia Torre. Microalgae for food use and Novel Foods regulation, 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. Plant-based alternatives to meats, 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 approuvé par le groupe de travail ‘Aliments non traditionnels’. 30.9.86
(10) The use of Spirulina aqueous extract is authorized in France but is not listed in the Novel Food Catalogue. Therefore, in order to find out whether its use is also allowed in the rest of Europe, it is necessary to send a request for consultation to the European Commission, in the manner prescribed by reg. EU 2018/456
(11) Dario Dongo, Andrea Adelmo Della Penna. Algae and microalgae for food use in Europe, ABC. GIFT (Great Italian Food Trade). 14.11.22
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
Graduated in Food Technologies and Biotechnologies, qualified food technologist, he follows the research and development area. With particular regard to European research projects (in Horizon 2020, PRIMA) where the FARE division of WIISE Srl, a benefit company, participates.
