Assessment of the Use of Coconut Water as a Cultivation Medium for Limnospira (Arthrospira) platensis (Gomont): Effects on Productivity and Phycocyanin Concentration

Due to the scarcity of sustainable inputs for photosynthetic microorganisms’ biotechnology, the search for natural substrates such as coconut water has gained prominence. This by-product is a substrate rich in macro- and micronutrients, as well as endogenous phytohormones that support microbial growth. In this context, this study aimed to use it as an alternative cultivation medium for Limnospira platensis (Gomont), formerly known as Arthrospira platensis, a high-value cyanobacterium. We evaluated growth parameters, phycocyanin concentration, purity, and biomass yield cultivated in coconut water and in SAG1x medium, a modified Zarrouk medium. Over 35 days of cultivation, both media efficiently supported cyanobacterial growth. In coconut water, the specific growth rate was 0.305 d−1, the maximum growth rate was 0.629 d−1, and the productivity was 0.256 g L−1 d−1. In SAG1x medium, the values obtained were 0.240 d−1, 0.676 d−1, and 0.218 g L−1 d−1, respectively. Phycocyanin obtained from cultivation in SAG1x medium presented food-grade purity (OD620/OD280 ratio > 0.7), while in coconut water, it was 0.6. The pigment concentration and yield in SAG1x (19.1 mg/L and 34.3%, respectively) also slightly exceeded those obtained with coconut water (14.3 mg/L and 25.5%, respectively). Despite this, the data reinforce the potential of coconut water as a viable and economically competitive alternative to conventional media for L. platensis production.