Plant melanin as a microcapsule wall component for flaxseed oil oxidative stability improvement

Flaxseed oil is very susceptible to oxidation due to high α-linolenic acid (ALA) content. Encapsulation is a widely used method to stabilize ALA. The aim of the current study was to compare the oxidative stability of flaxseed oil capsules made using black cumin and black sesame melanin extract. The prepared emulsions were spray-dried, and the particle size, shape, color, Carr's index, and oxidative stability of the obtained powders were measured. Oxidative stability was measured using the Rancimat, DPPH, and ABTS tests and by measuring the peroxide value and thiobarbituric acid reactive substances (TBARS) after UV irradiation of the powders. The results showed that the addition of melanin does not determine morphology and slightly enhanced the flowability of the powders. The longest induction period was recorded for 1% of black sesame melanin in the wall material. Black sesame melanin was also a good protective agent of flaxseed oil against oxidation under the influence of UV irradiation (the peroxide value was about 30% lower in the variant with 1% addition compared to the control sample) and showed a better antioxidant capacity in the ABTS assay. On the other hand, black cumin melanin showed a higher antioxidant capacity in the DPPH test. The results confirm the possibility of adding plant melanin to the material encapsulating flaxseed oil where they can act as light shielding and antioxidant agent.