Single-cell protein production potential with the extremophilic red microalgae Galdieria sulphuraria: growth and biochemical characterization

New food sources are urgently needed due to population growth. The production of microalgae biomass with high protein content is particularly of interest. Galdieria sulphuraria is an extremophilic red microalgae that can grow in acidic environments (pH 0 to 4) and above 40 degrees C. The aim of this work was to study the photoautotrophic growth and the biochemical composition of five G. sulphuraria strains to potentially produce single-cell protein. A kinetic study of cell growth and macromolecule content was performed in batch mode under controlled conditions: 42 degrees C, pH 2, constant illumination at 100 mu mol photons m(-2) s(-1), 150 rpm, 0.5 vvm, and atmospheric CO2 (0.04%). The G. sulphuraria CCMEE 5587.1 reached 2.33 g L-1 of dry cell weight (DCW) (similar to 9 x 10(7) cells mL(-1)) in 20 days, i.e., a productivity of similar to 110 mg(DCW) L-1 day(-1) was achieved. The biomass from this strain shows a high protein content (similar to 44% w/w(DCW)), 42.7% of essential amino acids, 4.7% (w/w(DCW)) of phycocyanin, 5.9% (w/w(DCW)) total carbohydrates, and 14.1% (w/w(DCW)) total lipids. A productivity of 21 t ha(-1) year(-1) could be attained assuming a straightforward scale-up in open ponds and reaching half the protein productivities obtained in the laboratory. This biomass composition is suitable for food purposes.