Fermentation of Chlorella vulgaris and Aphanizomenon flos-aquae biomass improves the antioxidant profile

Microalgae, known for their rich nutritional profile and bioactive molecules, have promising potential in nutraceutical applications. However, their rigid cell wall often limits the bioaccessibility of bioactive compounds. Fermentation offers a viable approach to improve the nutritional and functional properties of microalgae by breaking down complex macromolecules enhancing antioxidant capacity. This study investigated the fermentation of Chlorella vulgaris (Cv) and Aphanizomenon flos-aquae (Afa) with Saccharomyces cerevisiae and Lactobacillus plantarum over 24 and 48 h. The results showed a significant time-dependent increase in total polyphenol content: from 2.41 ± 0.29 to 6.06 ± 1.54 mg GAE/g in Cv and from 10.7 ± 0.57 to 15.95 ± 2.38 mg GAE/g in Afa after 48 h, although the total flavonoid content decreased in both microalgae. Antioxidant activity, evaluated by DPPH and ORAC assays, exhibited different trends. Cv showed a 1.6-fold increase in DPPH and a 2-fold increase in ORAC at both times, while Afa showed improved DPPH and ORAC values only after 24 h. Particularly, the cellular antioxidant activity in human erythrocytes revealed a significant effect of Afa fermentation at both time points. These findings suggest that fermentation can improve the polyphenol content and antioxidant properties of microalgae, especially in Aphanizomenon flos-aquae, indicating its potential for functional and nutraceutical food formulations.