Modeling and Optimizing the Effect of Light Color, Sodium Chloride and Glucose Concentration on Biomass Production and the Quality of Arthrospira platensis Using Response Surface Methodology (RSM)

Abstract

Arthrospira platensis (Spirulina) biomass is a valuable source of sustainable proteins, and the basis for new food and feed products. State-of-the-art production of Spirulina biomass in open pond systems only allows limited control of essential process parameters, such as light color, salinity control, or mixotrophic growth, due to the high risk of contaminations. Closed photobioreactors offer a highly controllable system to optimize all process parameters affecting Spirulina biomass production (quantity) and biomass composition (quality). However, a comprehensive analysis of the impact of light color, salinity effects, and mixotrophic growth modes of Spirulina biomass production has not been performed yet. In this study, Response Surface Methodology (RSM) was employed to develop statistical models, and define optimal mixotrophic process conditions yielding maximum quantitative biomass productivity and high-quality biomass composition related to cellular protein and phycocyanin content. The individual and interaction effects of 0, 5, 15, and 30 g/L of sodium chloride (S), and 0, 1.5, 2, and 2.5 g/L of glucose (G) in three costume-made LED panels (L) where the dominant color was white (W), red (R), and yellow (Y) were investigated in a full factorial design. Spirulina was cultivated in 200 mL cell culture flasks in different treatments, and data were collected at the end of the log growth phase. The lack-of-fit test showed that the cubic model was the most suitable to predict the biomass concentration and protein content, and the two-factor interaction (2FI) was preferred to predict the cellular phycocyanin content (p > 0.05). The reduced models were produced by excluding insignificant terms (p > 0.05). The experimental validation of the RSM optimization showed that the highest biomass concentration (1.09, 1.08, and 0.85 g/L), with improved phycocyanin content of 82.27, 59.47, 107 mg/g, and protein content of 46.18, 39.76, 53.16%, was obtained under the process parameter configuration WL4.28S2.5G, RL10.63S1.33G, and YL1.00S0.88G, respectively.

The Assessment of the Real-Time Radiative Properties and Productivity of Limnospira platensis in Tubular Photobioreactors

“…Lastly, the calculated TPBR mean areal productivity oscillates around 2.48 ± 0.06 [g m −2 day −1 ]. The latter value is up to six times lower than the reported areal productivities for similar PBRs [ 40 ], confirming the fact that the amount of light collected by the TPBR may be high, but the amount of energy supplied could be increased to improve the biomass productivity [ 41 ].…”

“…On the other hand, the efficiency in the use of photons is associated with the size of the complex light-capture antenna, which, as was highlighted in previous sections, in L. platensis suffers morphological changes regulated at the molecular level triggered by the naturally occurring stratification of light [ 23 , 30 ]. Even though there exists a clear dispersion over the biomass cultivation values that could be attributed to variations in other growth factors (such as varying temperatures [ 9 ] or nutrient starvation [ 40 ], oxygen mass transfer limitations and toxic effects of the oxygen evolution within the tubes [ 26 , 41 ] and poor mixing regime [ 25 ]), the predicted values show good agreement with the experimental values and the notion that light availability is the controlling factor driving the growth kinetics in the system under study. Lastly, the calculated TPBR mean areal productivity oscillates around 2.48 ± 0.06 [g m −2 day −1 ].…”

Effect of light spectrum, salinity, and glucose levels on Spirulina morphology

“…The Spirulina strain L. platensis PCC7345 was obtained from the Pasteur collection (PCC, Paris, France). Stock cultures were kept in modified Zarrouk's medium (Nosratimovafagh et al, 2022), sterilized through a 0.2‐μm filtration on a rotary shaker (150 rpm), 26°C, light intensity of 75 μmol m −2 s −1 , and 16:8 h of light:dark.…”

“…The composition of three light conditions was adjusted based on Mao and Guo (2018) using 20 LEDs including white (430–600 nm), blue (470 nm), yellow (590 nm), red (625 nm), and green (525 nm) (3 W, 3.5–3.2 V, 700 mA, 120° radiation angle, World Trading Net GmbH & Co. KG, Germany). Three light spectrum conditions were established based on Nosratimovafagh et al (2022): “white” (100% white), “red” (80% red, 15% blue, and 5% green), and “yellow” (80% yellow, 15% blue, and 5% green).…”

“…Due to the limited space for flasks on the shaker, the tests related to each set of light conditions were performed in two separate runs (six runs in total). The cultures (50 mL) were incubated for 3 days on a rotary shaker (200 rpm), 30 C, light intensity of 150 μmol m À2 s À1 , and 16:8 h of light:dark (Nosratimovafagh et al, 2022).…”