Giustino, Enrica (2024) Algaceutical: when microalgae application meets innovation. [Tesi di dottorato]

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Abstract

Microalgae are unicellular photosynthetic microorganisms that inhabit a wide range of environments and play a significant role in global oxygen production. Their remarkable adaptability to extreme external conditions makes them perfect candidates for sustainable biomass production in regions unsuitable for conventional agriculture. Microalgae can produce a wide variety of bioactive molecules (i.e., phycobiliproteins, carotenoids, lipids, polysaccharides), many endowed with antioxidant properties. In recent years, the potential of microalgae has been increasingly recognized for various industrial applications, including nutraceuticals, cosmeceuticals, biofuels, and pharmaceuticals. In particular, research on the antioxidant potential of microalgae-derived compounds is gaining traction, as oxidative stress is now well recognized for its role in the alteration of cellular differentiation as well as in the modification of different metabolic pathways, like the lipidic ones, which can lead to the onset of a plethora of associated pathologies. The general aim of the present thesis was to evaluate the potential of antioxidant molecules derived from microalgae in different applications, such as the cosmeceuticals and nutraceuticals fields. Investigation was done with a specific emphasis on the impact of different antioxidant molecules on cellular differentiation in murine pre-adipocytes and on lipid metabolism in mature adipocytes and hepatocytes. Three microalgal strains were used: Porphyridium cruentum, a red marine mesophile microalga, Galdieria phlegrea, a red thermo-acidophilic microalga, and Pseudococcomyxa simplex, a green freshwater microalga. The first two strains were already the subject of a tailored biorefinery approach, which allowed obtaining different classes of bioactive molecules, characterized at chemico-physical and antioxidant level. In this study, sulfated exopolysaccharides and phycoerythrin from P. cruentum, and carotenoids from G. phlegrea residual biomass (i.e., after protein extraction) were used. Results showed that sulfated exopolysaccharides, phycoerythrin and carotenoids were all biocompatible and able to inhibit pre-adipocyte differentiation, but with a different extent. Interestingly, carotenoids from the residual biomass of G. phlegrea showed a regulation of lipid metabolism on mature adipocytes, whereas sulfated exopolysaccharides positively inhibited lipid build-up in the hepatic cells. For P. simplex, the study started with the design of a novel biorefinery, which enabled the extraction of carotenoids and lipids and the evaluation of the antiadipogenic activity of the extracted carotenoids. Finally, flocculation was explored as an alternative harvesting method, and its efficacy was evaluated through the biological characterization of the extracted molecules after flocculation.

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