Biochemical and Antioxidant Characterization of Pigment-Deficient Chlorella vulgaris Flours and the Impact of Fermentation: Comparative Insights from Green, Honey, and White Variants

This study investigated the biochemical composition and antioxidant potential of flours from pigment-deficient <i>Chlorella vulgaris</i> variants (honey and white) and wild-type (green) and the impact of lactic acid bacteria-yeast co-culture fermentation. The three variants were characterized for composition, total polyphenol (TPC) and flavonoid (TFC) contents, antioxidant capacity (DPPH, FRAP, and ORAC assays), and reactive oxygen species production in HT-29 intestinal cells. All extracts were noncytotoxic up to 100 µg/mL. Among all variants, the green showed the highest native TPC, TFC, and overall antioxidant activity. TPC and TFC were similar between honey and white, while FRAP was higher in honey and ORAC was higher in white. Biomasses were subsequently fermented for 24 h using <i>Lactiplantibacillus plantarum</i> CR L1 or <i>Levilactobacillus brevis</i> L204 with either <i>Saccharomyces cerevisiae</i> TRE Y100 or <i>Kluyveromyces marxianus</i> MK Y55. Fermentation resulted in significant pH reduction and increases in titratable acidity and lactic acid production, particularly in co-cultures involving <i>K. marxianus</i>. However, the effects on antioxidant properties were strongly matrix-dependent, with significant increases in TPC and antioxidant activity observed only in the white variant. Overall, pigmentation and microbial pairing emerged as key determinants of metabolic outcomes. These findings highlight the potential of co-culture fermentation to enhance the bioactive profile of pigment-deficient <i>C. vulgaris</i>, supporting their application in functional foods.