Exploring the Development of a Clean-Label Vegan Burger Enriched with Fermented Microalgae

<i>Haematococcus pluvialis</i> and <i>Porphyridium cruentum</i> are red microalgae with high biotechnological potential due to their rich composition of bioactive compounds. However, their intense flavor limits their application in food products. This study evaluated the impact of fermentation with <i>Lactiplantibacillus plantarum</i> (30 °C for 48 h; LAB-to-biomass ratio of 0.1:1; 10⁶ CFU/mL) on the physicochemical and functional properties of <i>H. pluvialis</i> and <i>P. cruentum</i> biomasses. Particular attention was given to antioxidant activity (ABTS and ORAC assays), color, amino acid profiles, and volatile organic compound (VOC) profiles, all of which may influence sensory characteristics. Results demonstrated that non-fermented <i>H. pluvialis</i> exhibited significantly higher antioxidant activity (AA) than <i>P. cruentum</i>. After fermentation, <i>H. pluvialis</i> showed an ABTS value of 3.22 ± 0.35 and an ORAC value of 54.32 ± 1.79 µmol TE/100 mg DW, while <i>P. cruentum</i> showed an ABTS of 0.26 ± 0.00 and an ORAC of 3.11 ± 0.13 µmol TE/100 mg DW. Total phenolic content (TPC) of fermented <i>H. pluvialis</i> and <i>P. cruentum</i> was 1.08 ± 0.23 and 0.18 ± 0.026 mg GAE/100 mg DW, respectively. Both AA and TPC increased after fermentation. Fermentation also significantly affected biomass color. FTIR analysis showed intensification of protein and carbohydrate vibrational bands post-fermentation. GC-MS analysis of VOCs showed that <i>P. cruentum</i> contained 42 VOCs before fermentation, including <i>trans-</i>β-ionone, 4-ethyl-6-hepten-3-one, hexanal, and heptadienal, which are responsible for fishy and algal odors. Fermentation with <i>Lb. plantarum</i> significantly reduced these compounds, lowering <i>trans-</i>β-ionone to 0.1453 mg/L and eliminating 4-ethyl-6-hepten-3-one entirely. <i>H. pluvialis</i> contained 22 VOCs pre-fermentation; fermentation eliminated hexanal and reduced heptadienal to 0.1747 ± 0.0323 mg/L. These changes contributed to improved sensory profiles. Fermentation also induced significant changes in the amino acid profiles of both microalgae. The fermented biomasses were incorporated into vegan burgers made from chickpea, lentil, and quinoa. Color evaluation showed more stable and visually appealing tones, while texture remained within desirable consumer parameters. These findings suggest that <i>Lb. plantarum</i> fermentation is an effective strategy for improving the sensory and functional characteristics of microalgal biomass, promoting their use as sustainable, value-added ingredients in innovative plant-based foods.