Biochemical Characterization of Japanese Spirulina sp. Microalgal Powder: Pigment, β-Carotene, and Phenolic Profiling with Antioxidant Assessment

Background: Spirulina microalgae are filamentous, multicellular, blue–green cyanobacteria that serve as popular nutritional sources in medicine, the food industry and aquaculture. Spirulina has a high content of macro- and micronutrients, antioxidants and pigments such as carotene, chlorophyll and phycocyanin. Aims: This study aimed to determine the pigment, β-carotene, phenolic, and antioxidant profile of Japanese Spirulina microalgal powder as a basis for evaluating its relevance to future functional food and nutraceutical development. Materials and Methods: The characteristics of the powder were assessed by visual inspection and optical microscopy. Pigment (carotenoid and chlorophyll) contents were determined by UV-Vis spectrophotometry. β-carotene was quantified by reversed-phase HPLC using an isocratic elution programme with a mobile phase of dichloromethane:acetonitrile:methanol (40:45:15, v/v/v). Total phenolic content and antioxidant activity were assessed using the Folin-Ciocalteu and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays, respectively. Results: The microalgal powder was a uniform, homogeneous substance with a slightly fishy odour, appropriate for analysis. Total carotenoid and chlorophyll contents reached 3.306 mg/g DW and 6.471 mg/g DW, respectively. The retention time of β-carotene was approximately 11.827 minutes, and the linear regression equation showed statistical significance (R² = 0.9995); the β-carotene content of the microalgal powder was 2.677 mg/g DW. Total phenolic content was 0.444 mg GAE/g DW, and DPPH radical scavenging activity was 25%, equivalent to 2.487 µg/mL of vitamin C. Conclusions: The Japanese Spirulina sp. microalgal powder possessed a stable, well-characterised biochemical composition — carotenoids, chlorophylls, β-carotene and phenolics — together with measurable in vitro antioxidant activity. These findings support its potential as a biochemically characterised ingredient for further investigation in functional food and nutraceutical research.