Comparative analysis of bacterial and microalgal natural astaxanthin: Part II — Biocompatibility, bioaccessibility, encapsulation, mutagenicity, and aquatic toxicity

Astaxanthin (AXT) is a potent antioxidant with applications in food, pharmaceutical, and cosmetic industries. While Haematococcus pluvialis (a microalga) is the only natural AXT source approved for human use, bacterial alternatives such as Paracoccus carotinifaciens are gaining attention for their sustainable production potential. This study, Part II of a comparative research analysis between AXT from H. pluvialis and P. carotinifaciens, explores key aspects of biocompatibility, bioaccessibility, encapsulation performance, mutagenicity, and aquatic toxicity. The HET-CAM confirmed that both AXT sources are non-irritant. In vitro digestion revealed that H. pluvialis AXT undergoes greater solubilization in the gastric phase but experiences higher losses in the intestinal phase, while P. carotinifaciens AXT demonstrates better retention. Nanoemulsions of both extracts showed high encapsulation efficiency (99 %) and colloidal stability, with bacterial AXT forming smaller, more stable droplets. Ames mutagenicity assays with five Salmonella strains showed no evidence of mutagenic activity. Additionally, no acute toxicity was observed in Daphnia similis, even at the highest tested concentrations. These findings reinforce the safety and functionality of both microbial AXT sources, supporting P. carotinifaciens as a promising alternative for future nutraceutical and pharmaceutical applications.