• antioxidant microalgae
• carotenoid
• physiology

Carotenoids act as potential anti-oxidant, quenching excited energy of singlet oxygen and scavenging free radicals. It is well-known that under stress conditions photosynthetic organisms are able to synthesize large amount of carotenoids, which ca be considered as a natural source of antioxidant and anti-aging substances, i.e. astaxanthin, zeaxanthin, lutein, considered very powerful antioxidants. The microalgae Haematococcus pluvialis and Chlamydomonas reinhardtii are able to synthesize large amount of carotenoids and represent both a suitable source of antioxidant compounds. Under high light exposure and nutrient starvation both H. pluvialis and C. reinhardtii exhibited an increased capability to synthesize antioxidant carotenoids, such as astaxanthin, lutein and zeaxanhtin. In addition the screening of C. reinhardtii D1 protein mutants evidenced how the functionality of this protein was implicate in the photosynthetic activity of this microalga, promoting photoprotective responses at different level. In particular the mutant strains exhibited a strong induction of the xanthophylls cycle and lutein synthtesis under sulfur starvation and anaerobic conditions. The algal extracts exhibited an anti-inflammatory activity. The results indicated that these microalgae can represent a useful source of antioxidant compounds for application in human health.