Estrazione di astaxantina con approcci ecosostenibili da colture ottimizzate di Haematococcus pluvialis

A great interest in microalgae bioactive compounds is spreading internationally for numerous commercial uses. The present thesis involves the production and the extraction of a secondary ketocarotenoid, astaxanthin (3,3'-dihydroxy-β, β'-carotene-4,4'-dione), from Haematococcus pluvialis applying bio- and eco-compatible methodologies. Astaxanthin is naturally accumulated when the microalgae are submitted to environmental stress, changing from a green vegetative phase to a red cyst phase. The results showed that the polysaccharide content increases while proteins and fatty acids decrease by intensifying the production of astaxanthin in the red phase. Furthermore, the biochemical composition of cells in the two growth phases varies qualitatively and quantitatively in total lipids, especially in carotenoid content and composition. Various sustainable solvents have been here used for the development of astaxanthin extraction protocols. The highest yields were obtained with 2-methyltetrahydrofuran, dimethyl carbonate and ethyl acetate; however these solvents were not algae compatible, causing algal death. On the other hand, vegetable oil maintained algal vitality and provided modest yields of extraction. Re-inducing the vegetative phase and subsequently the red one in algal cells recovered from a first extraction process with oil, the yield in astaxanthin of the second extractive cycle was 3 times higher than the previous one. Astaxanthin is therefore potentially obtainable with two alternative approaches: i) with good extraction yields using sustainable solvents (eg 2-methyltetrahydrofuran) or solvents that are safe for humans (eg methyl isobutyl ketone, isoamyl-acetate, butanol, ethyl acetate), but incompatible with cellular vitality; ii) with lower yields and longer extraction time using vegetable oils, capable of maintaining algal vitality and suitable for applications in the nutraceutical, cosmetic and food industries.