Ultrafiltration for the assessment of supernatants and biomass from Spirulina cultures supplemented with L-tryptophan

Spirulina, a cyanobacterium renowned for its nutritional value, has recently gained attention as an agricultural biostimulant due to its plant growth-promoting properties. On the fifth day of cultivation, L-tryptophan (1.0 g/L) -a precursor to phytohormones like indole-3-acetic acid (IAA)-was supplemented, leading to the production of 100 mg/L of IAA and 3 mg/L of total carotenoids in the supernatant after 100 h. Ultrafiltration concentrated these molecules, achieving recoveries of 33 % for IAA and 31 % for carotenoids, along with a 12-fold concentration factor. The lyophilized retentate, rich in IAA and carotenoids, was applied to mung bean plants, where an application of 0.2 mg/L of IAA increased secondary root length by 18 % and the number of roots by 35 %. Additionally, the biomass was processed to produce a powder rich in phycocyanin, chlorophyll a, carotenoids, and proteins, making it suitable for cosmetic formulations. This dual approach enables the sustainable utilization of Spirulina, using the biomass for cosmetics and the supernatant in agriculture, with ultrafiltration effectively reducing water content and preserving active compounds.