Microbial decontamination and enhanced extraction of value-added compounds from Spirulina platensis using gamma radiation

Spirulina platensis has garnered increasing attention as a valuable source of proteins, lipids, and pigments, with applications in the food, feed, and nutraceutical industries. However, large-scale cultivation in open pond systems is liable to microbial contamination, posing risks to product quality and productivity. This study evaluated the effects of gamma (γ) irradiation up to 10 kilogray (kGy) as a dual strategy for microbial decontamination and enhanced extraction of bioactive compounds from dried Spirulina powder. A dose of 4 kGy resulted in a substantial reduction in microbial populations, while irradiation at 6 kGy reduced microbial counts to levels below the detection limit of the applied culture-based methods, indicating effective decontamination. The D₁₀-values obtained for Bacillus sp. (0.44 kGy), Staphylococcus aureus (0.41 kGy), and Pseudomonas aeruginosa (0.58 kGy) demonstrate species-dependent radiosensitivity. Analyses using electron spin resonance (ESR), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and lipid peroxidation assays demonstrated that γ-irradiation preserved the structural integrity of key biomolecules. Biomass irradiated at 6 kGy exhibited the highest recovery of lipid (60.83 ± 1.38 mg g⁻¹), protein (547.43 ± 2.97 mg g⁻¹), and carbohydrates (275.60 ± 2.50 mg g⁻¹). Pigment extraction also increased, yielding elevated levels of chlorophyll a (11.40 ± 0.10 mg g⁻¹), carotenoids (3.48 ± 0.30 mg g⁻¹), and phycobiliprotein (125.20 ± 0.70 mg g⁻¹). Antioxidant activity peaked at 69.61 ± 1.47% at the same dose, associated with enhanced phenolic content. Overall, γ-irradiation represents a promising biotechnological tool for producing microbiologically safe Spirulina biomass while improving the extraction of value-added bioactive compounds for nutraceutical and pharmaceutical applications.