Seasonal biochemical fingerprints of outdoor cultivated Spirulina (Limnospira platensis) and Microchloropsis gaditana: insights into compositional and functional shifts

Microalgae are increasingly recognized as sustainable bioresources with applications in food, feed, nutraceuticals, and aquaculture. Among them, Spirulina (Limnospira platensis) and Microchloropsis gaditana (formerly Nannochloropsis gaditana) stand out due to their rich biochemical composition with industrial applications and high market value. This study separately investigates the seasonal variability in the biochemical composition of L. platensis cultivated in open raceway ponds and M. gaditana grown in closed photobioreactors. The results suggest a response to seasonal changes. L. platensis exhibited higher protein content in spring (47.82%) and summer (45.48%), while carbohydrate accumulation peaked in winter (50.85%). M. gaditana showed increased lipid (21.67%) and carbohydrate (14.56%) content in autumn compared to winter and summer, but with lower variations in response to seasonal environmental changes. This microalga exhibited higher FA 20:5 n-3 (EPA) levels in winter compared to summer, suggesting its potential as a sustainable EPA source during colder months. The dominant carbohydrate residue in both microalgae, present throughout all seasons, was glucose, which could be associated with the presence of β-glucans, in addition to glycogen, reinforcing their bioactive potential. Pigment composition was also seasonally influenced in L. platensis, which accumulated more chlorophyll and phycocyanin in spring and summer, whereas M. gaditana showed elevated levels of neoxanthin in autumn and winter, and violaxanthin in spring. Although limited by a single sampling per season and the different cultivation systems size, this study provides preliminary observations of seasonal variations in biomass composition, highlighting that biochemical composition varies with season in a species-specific manner. Understanding these variations improves our knowledge of microalgal biochemical plasticity under outdoor conditions.