@phdthesis{77994, type = "Thesis", year = "2020", title = "Évaluation des microalgues sélectionnées en Nouvelle-Calédonie comme source potentielle d'anti-oxydants naturels. Identification des molécules anti-radicalaires et stimulation de leur biosynthèse par orientation métabolique", journal = "", editor = "", volume = "", number = "", pages = "", author = "Coulombier Noémie", url = "https://archimer.ifremer.fr/doc/00668/77994/", organization = "", address = "FRANCE", school = "Université de la Nouvelle-Calédonie", abstract = "
The demand has increased for natural antioxidant as an alternative to synthetic antioxidant for food, cosmetic and nutraceutical industry. Most natural antioxidant currently available on the market are derived from terrestrial plant. However, microalgae, with their chemodiversity, productivity and controlled cultivation possibilities, are a promising source of antioxidant.
The objective of this thesis is to evaluate the potential of microalgae isolated in New Caledonia as a source of natural antioxidants. About thirty species of microalgae were isolated in the caledonian lagoon for their high growth rate by a dilution-exclusion method. A screening of antioxidant activity was then carried out on twelve species, grown at two light intensities (low and high), using four different antioxidant assays: DPPH (2,2-diphenyl-1-picrylhydrazyl), TEAC (Trolox equivalent antioxidant capacity), ORAC (Oxygen Radical Absorbance Capacity) and TBARS (Thiobarbituric Acid Reactive Substances). The results of the antioxidant screening showed the need to use several antioxidant assays and the significant impact of light intensity on antioxidant activity. The screening also highlighted two species of interest, Nephroselmis sp. and Tetraselmis sp.. The influence of some culture parameters on antioxidant activity was studied for these two species.
Nephroselmis sp. has a strong capacity to scavenge peroxyl radicals owing to its high carotenoid content. In addition, this species has a carotenoid of interest that is still little studied, siphonaxanthin. It has been shown that the cultivation of Nephroselmis sp. should not be limited in nitrogen to promote the production of antioxidant carotenoids, in particular siphonaxanthin.
Tetraselmis sp. has been shown to have a strong capacity to inhibit lipid peroxidation. The study of the influence of pH (6.5 and 8.5) and culture mode (batch vs. continuous) on the antioxidant activity and photophysiology of Tetraselmis sp. highlighted the importance of these two parameters on the antioxidant activity which is optimized when the microalgae is in a good physiological state.
These results reveal the potential of microalgae isolated in New Caledonia as a source of natural antioxidants, and the high impact of culture conditions on antioxidant activity. Knowledge of the different mechanisms must now be deepened on cellular models and the origin of the molecules involved must be characterized by a metabolomic approach.