Cell disruption of microalga Nannochloropsis oceanica using bead milling: Effect on recovery, composition, and bioaccessibility of partially disrupted biomass

The microalga Nannochloropsis oceanica is a promising source of valuable nutrients such as protein, omega-3 fatty acids, and vitamins. Unfortunately, these compounds are protected by a tough cell wall that hampers digestibility. The present study evaluated bead milling for cell disruption of N. oceanica, with focus on biomass recovery, composition, and in vitro bioaccessibility. Suspensions of lyophilized biomass were subjected to different milling severities while determining the disruption level and dry matter recovery. The concentration of amino acids, fatty acids, and vitamin K were determined before and after milling. Potential changes in vitamin K and fatty acid bioaccessibility were assessed using the INFOGEST 2.0 model, complemented with visual observations using scanning electron microscopy. With the chosen milling parameters (agitator speeds 6 m·s⁻¹ and 12 m·s⁻¹ + treatment times 1.0, 2.5, 5.0 min), 20–70 % cell disruption was achieved. Dry matter recovery decreased from 100 % (non-disrupted) to 69 % for the most disrupted sample. Bead milling showed no significant impact on the concentration of total amino acids, total fatty acids, EPA, and MK-4. These components remained relatively stable at 310–330 mg AA·g⁻¹ DM, 210–240 mg FA·g⁻¹ DM, 23–28 mg EPA·g⁻¹ DM, and 70–85 μg MK-4·g⁻¹ DM. Bead milling did not significantly influence the bioaccessibility of EPA and MK-4, which remained anchored at 8–12 %, despite clear structural alterations in the processed biomass. The results verify bead milling as an effective cell disruption method for N. oceanica but also indicate that this alone does not ensure improved in vitro bioaccessibility of intracellular nutrients.