The optimal culture media for crude protein and polyunsaturated fatty acid production from Isochrysis galbana and Nanochloropsis oculata for livestock and aquatic species nutrition

This study aimed to investigate the effect of different culture mediums based on the Walne medium on the growth rate, chemical composition, and fatty acid (FA) profile in I. galbana and N. oculata. This experiment was done in a factorial design with two culture media (Walne and modified Walne media) and two microalgae species, including I. galbana and N. oculata. The results showed that the modified culture medium increased total and daily fresh and dried biomass production of I. galbana and N. oculata. Modified culture media increased crude fat (CF) and crude protein (CP) content and total and daily lipid production in both the studied species. However, in both the studied culture mediums, N. oculata had higher growth and production performance compared to I. galbana. Modified growth media also affects the FA profiles of the studied microalgae species. Total saturated and unsaturated FA content was not influenced by the growth medium but modified media increased poly unsaturated FA (PUFA) at the expense of mono unsaturated FA (MUFA). Omega- 3 FA content (linolenic acid, Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA)) was increased as a result of the medium modification in both species. However, linoleic acid content was affected differently in I. galbana and N. oculata. The linoleic acid concentration was reduced in modified medium grown N. oculata but increased in I. galbana. Palmitic acid and stearic acid contents were also decreased in both of the studied species in the modified medium. This study develops microalgal cultivation using a modified Walne medium for higher CP, CF, EPA, DHA contents, the ratio of omega3: omega6 FA, and biomass production in N. oculata and I. galbana microalgae.
Microalgae species can produce oil and protein in non-cultivable lands, reducing the need for defrosting and can have an important role in reducing carbon foot-print of animal production. One of the most valuable products of microalgae is their oil, which ranges from 20 to 50% of the dry weight of microalgae (Brennan and Owende 2010; Leonga et al. 2018). The I. galbana is often grown on farms to produce oils that contain large amounts of PUFA rich in omega-3 long chain FA, such as EPA and DHA (Gouveia et al. 2008). Species of the genus N. oculata are also known to be rich in EPA (Kagan et al. 2014; Borges et al. 2016).
Factors such as nutrient quantity and quality, light, pH, turbulence, salinity, and temperature are the most important parameters on which, the growth of microalgae depends (Lavens and Sorgeloos 1996; Converti et al. 2009; Emmanuel and Nelson 2016). Vitamins regulate biochemical reactions in microalgae (Hakalin et al. 2014) and the growth rate of some microalgae species is highly dependent on some the vitamins such as cobalamin, biotin and thiamine (Tandon et al. 2017). However, the effect of vitamins on the growth, diversity, and productivity of microalgae has been poorly studied (Arif et al. 2019).
The effects of different Nitrogen and phosphorus concentration as the main limiting nutrients on growth performance and biomass production of I. galbana and N. oculata had been evaluated previously (Andersen 2005; Zarrinmehr et al. 2020). However, there was not any report about effects of modifying the availability of culture medium sources of nitrogen and phosphorus. In the composition of the Walne medium, No3-, Po4-, and Cl- are considered as anions, and Na+, Mn+, Co+, Zn+, and Cu+ are considered as cations. Cations chelating anions and making them less available to microalgae. So, we hypothesize that changing the concentration of cations in the culture media, without increasing the concentration of N and P sources, will change the availability of anionic compounds for microalgae and consequently affects microalgal production and composition. Therefore, the effects of lower levels of cations including ZnCl2, CoCl2. 6H2O, (NH4)6Mn7O24, and CuSo4. 5H2O and higher levels of B1 and B12 vitamin in Walne medium on the growth rate, biomass production performance, chemical composition, and fatty acid profile of I. galbana and N. oculata, were investigated in this study.

This study aimed to investigate the effect of different culture mediums based on the Walne medium on the growth rate, chemical composition, and fatty acid (FA) profile in I. galbana and N. oculata. This experiment was done in a factorial design with two culture media (Walne and modified Walne media) and two microalgae species, including I. galbana and N. oculata. The results showed that the modified culture medium increased total and daily fresh and dried biomass production of I. galbana and N. oculata. Modified culture media increased crude fat (CF) and crude protein (CP) content and total and daily lipid production in both the studied species. However, in both the studied culture mediums, N. oculata had higher growth and production performance compared to I. galbana. Modified growth media also affects the FA profiles of the studied microalgae species. Total saturated and unsaturated FA content was not influenced by the growth medium but modified media increased poly unsaturated FA (PUFA) at the expense of mono unsaturated FA (MUFA). Omega- 3 FA content (linolenic acid, Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA)) was increased as a result of the medium modification in both species. However, linoleic acid content was affected differently in I. galbana and N. oculata. The linoleic acid concentration was reduced in modified medium grown N. oculata but increased in I. galbana. Palmitic acid and stearic acid contents were also decreased in both of the studied species in the modified medium. This study develops microalgal cultivation using a modified Walne medium for higher CP, CF, EPA, DHA contents, the ratio of omega3: omega6 FA, and biomass production in N. oculata and I. galbana microalgae.