Foods · 5 authors, 1 centre
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This study evaluated the marine microalga *Tisochrysis lutea* as a fermentation substrate for *Lactiplantibacillus plantarum*. Fermentation reduced carbohydrate and fucoxanthin content but improved pigment extractability and radical scavenging activity in diluted MRS medium. The microalgal biomass did not protect the probiotic bacterium during simulated digestion, but showed potential as a prebiotic substrate for further investigation.
**Background:** Microalgae are promising sources of high-quality proteins, polyunsaturated fatty acids, and bioactive molecules for functional foods. *Tisochrysis lutea* is a marine haptophyte rich in DHA, fucoxanthin, proteins, and fibers, but is not yet approved for human food use. Fermentation with lactic acid bacteria could improve the functional properties and organoleptic characteristics of microalgal biomass. This study aimed to evaluate *T. lutea* F&M-M36 as a substrate for lactic acid fermentation, investigate the prebiotic potential of its indigestible fraction, and assess the effect of fermentation on functional properties and probiotic survivability during simulated digestion.
**Methods:** *T. lutea* F&M-M36 lyophilized biomass was characterized for biochemical composition (protein, carbohydrate, lipid, ash, total dietary fibers, fucoxanthin, total carotenoids). Three lactic acid bacteria (*L. plantarum* ATCC 8014, *L. bulgaricus* LB28A, *L. casei* LB28B) were screened for growth rate and survivability to in vitro simulated digestion (pepsin at pH 2.0 followed by pancreatin at pH 6.5). *L. plantarum* was selected for fermentation trials. Fermentation was conducted over 72 h with raw biomass or post-digestion residue suspended in either water or MRS 1:3 (one-third strength MRS). Controls included MRS 1:1, MRS 1:3, and sodium alginate in MRS 1:3. Bacterial growth (CFU), pH, lactic acid, and acetic acid were monitored at 0, 24, 48, and 72 h. Fermented materials were analyzed for biochemical composition, digestibility (Boisen and Fernández method modified by Niccolai et al.), radical scavenging activity (DPPH assay), pigment content (chlorophyll a, chlorophyll c, total carotenoids), and total phenolic content (Folin-Ciocalteu). Bacterial survivability after fermentation was also tested.
**Key Results:** *L. plantarum* showed the highest growth rate (0.33 h⁻¹ by OD600, 0.48 h⁻¹ by Neubauer chamber) and the best survivability to in vitro digestion (2.6% after pepsin, 1.5% after pancreatin), compared to *L. bulgaricus* (0.3% and 0.01%) and *L. casei* (<0.01% and <0.001%). During fermentation, *L. plantarum* reached 8.8 log CFU mL⁻¹ with raw biomass in water (at 48 h) and 8.5 log CFU mL⁻¹ in MRS 1:3 (at 24 h). Post-digestion residue supported lower growth (max 7.8 log CFU mL⁻¹ in MRS 1:3). Lactic acid reached 4.9 g L⁻¹ with raw biomass in MRS 1:3, while in water it was ≤0.35 g L⁻¹. Acetic acid production was generally lower (max 1.7 g L⁻¹ with alginate). Fermentation significantly reduced carbohydrate content (from 12.6% to 7.2–7.9% dry weight) and fucoxanthin (from 5.86 to 1.88–2.00 mg g⁻¹) in raw biomass. Total carotenoids decreased from 20.8 to 12.3–13.3 mg g⁻¹. Digestibility of raw biomass was approximately 65% and did not differ significantly between unfermented and fermented samples. Radical scavenging activity in CHCl₃:MeOH 1:2 extracts was significantly higher in raw biomass fermented in MRS 1:3 (58% RSA) compared to unfermented (30%) or water-fermented (27%). Total phenolic content in CHCl₃:MeOH 1:2 extracts ranged from 20.8 to 35 mg GAE g⁻¹, with no significant differences among treatments. Bacterial survivability after fermentation was about 1% (MRS 1:3) and 6.6% (water) after pepsin, decreasing to <0.01% and 0.06% after pancreatin, with no significant differences between matrixes.
**Clinical Implications:** This study provides foundational data for developing *T. lutea* as a functional food ingredient through fermentation. The biomass supports *L. plantarum* growth and fermentation improves extractability of pigments and antioxidant activity, particularly in a diluted organic medium. However, the microalgal biomass did not protect the probiotic bacterium during simulated digestion, and survivability was low (<1% after full digestion). The post-digestion residue showed limited prebiotic potential for *L. plantarum*, but further testing with colon-resident bacteria is needed. The reduction in fucoxanthin during fermentation (68% loss) is a limitation. The authors note that fermentation appeared to reduce the strong smell of *T. lutea*, which could improve palatability. Regulatory approval of *T. lutea* as a food ingredient would facilitate further research and commercial development of fermented microalgal products.