The Effect of pH on Contamination Reduction and Metabolite Contents in Mass Cultures of Spirulina (Arthrospira platensis Gomont)

The microalgae Spirulina (Arthrospira platensis Gomont) is already cultured commercially using open ponds. The obstacle to mass cultivation of Spirulina is maintaining the monoculture without any contamination that can affect biomass products and their metabolites. The tolerance of Spirulina to environmental changes, such as changes in pH conditions, can be used as a method to overcome contamination in Spirulina mass cultivation. The growth contaminant can be avoided or controlled by giving mechanical stress by modifying the pH to alkaline levels. The efficient use of cost-effective materials in mass cultivation prevents contamination and maintains Spirulina's productivity. This study investigated the optimal pH parameters of 7–11 for 10 days. Cell density and dry biomass were measured daily using a hemocytometer and filter paper Whatman. The growth rate of contaminant microorganisms was carried out every five days along ten days of cultivation using the Total Plate Count (TPC) method. Using pH 9 effectively increased the cell density significantly (9.12±1.02%) and dry biomass (17.31±4.19 g.mL−1), reducing the contaminants in Spirulina mass cultures. The metabolite content was measured, including total protein using the Kjeldahl method, total lipid using the Soxhlet method, and pigmentations (such as chlorophyll, carotene, and phycocyanin) using spectrophotometry. The pH scale 8–10 can increase protein, lipid, and pigmentations. However, the pH 11 decreased almost entirely as a result of the metabolite contents of Spirulina.