Publicação
Valorisation of extremophilic microalgae isolated from lichens: development of cultivation and extraction strategies for high performance production of bioactive compounds
| Resumo: | Lichens are constituted by microalgae (the photobiont), associated with a fungus (the mycobiont), that are often subjected to extreme conditions, resulting in the production of a variety of bioactive compounds. However, lichens have not been considered as a potential commercial source of these compounds mostly due to their extremely low growth rates. In this work we propose a disruptive approach that can be a game changer in the prospection of sustainable sources of bioactive compounds. Eighteen lichens were collected in the north of Portugal. From those, it was possible to isolate and cultivate eight photobionts. The extracts of the eight photobionts showed relevant antioxidant activity. Photobionts that belong to the Coelastrella genus showed the highest hyaluronidase inhibition, anti-inflammatory activity, a high inhibitory power of α-amylase and α-glucosidase and a selective cytotoxicity, inhibiting the growth of cancer cells. The combined use of variations of temperature (10 and 40 °C), light intensity (10 and 250 μmol.photons.m-2.s-1), and pH (4 and 10) were evaluated to understand if these environmental parameters can interfere in the productivity and quantity of biochemical compounds produced by the Coelastrella sp. Temperature of 17.5 °C, light intensity of 250 μmol.photons.m-2.s-1 and pH 7 was the combination that promoted the highest biomass productivity (0.0469 g.L-1.d-1). Significant effects were achieved over pigments, proteins, carbohydrates, and lipids concentration. Proteins were the biochemical group of compounds that showed the highest production in Coelastrella sp. The influence of different photobioreactors (bubble column, flat panel and split cylinder airlift) on the growth and productivity of Coelastrella sp. was evaluated. The SCA presented the highest biomass productivity of 0.113 ± 0.019 g.L-1.d-1 and specific growth rate of 0.187 ± 0.00913 d-1. In order to maximize the extraction efficiency of bioactive compounds, five different cell disruption methods have been optimized: Freeze-Thaw cycles; bead milling; high-speed homogenization; microwave and sonication. Sonication and bead milling proved to be the most efficient processes in cell disruption and release of biochemical compounds, however, when considering also the energy consumption, bead milling was the most efficient method. The results obtained in this thesis proved that photobiont extracts isolated from lichens are a promising source of bioactive compounds, thus confirming the high potential of these microorganisms in the biotechnological field. |
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| Autores principais: | Loureiro, Luís Carlos Sá |
| Assunto: | Lichens Photobiont Bioactive compounds Cultivation strategy Cell disruption Líquens Fotobionte Compostos bioativos Estratégia de cultivo Rutura celular |
| Ano: | 2022 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Lichens are constituted by microalgae (the photobiont), associated with a fungus (the mycobiont), that are often subjected to extreme conditions, resulting in the production of a variety of bioactive compounds. However, lichens have not been considered as a potential commercial source of these compounds mostly due to their extremely low growth rates. In this work we propose a disruptive approach that can be a game changer in the prospection of sustainable sources of bioactive compounds. Eighteen lichens were collected in the north of Portugal. From those, it was possible to isolate and cultivate eight photobionts. The extracts of the eight photobionts showed relevant antioxidant activity. Photobionts that belong to the Coelastrella genus showed the highest hyaluronidase inhibition, anti-inflammatory activity, a high inhibitory power of α-amylase and α-glucosidase and a selective cytotoxicity, inhibiting the growth of cancer cells. The combined use of variations of temperature (10 and 40 °C), light intensity (10 and 250 μmol.photons.m-2.s-1), and pH (4 and 10) were evaluated to understand if these environmental parameters can interfere in the productivity and quantity of biochemical compounds produced by the Coelastrella sp. Temperature of 17.5 °C, light intensity of 250 μmol.photons.m-2.s-1 and pH 7 was the combination that promoted the highest biomass productivity (0.0469 g.L-1.d-1). Significant effects were achieved over pigments, proteins, carbohydrates, and lipids concentration. Proteins were the biochemical group of compounds that showed the highest production in Coelastrella sp. The influence of different photobioreactors (bubble column, flat panel and split cylinder airlift) on the growth and productivity of Coelastrella sp. was evaluated. The SCA presented the highest biomass productivity of 0.113 ± 0.019 g.L-1.d-1 and specific growth rate of 0.187 ± 0.00913 d-1. In order to maximize the extraction efficiency of bioactive compounds, five different cell disruption methods have been optimized: Freeze-Thaw cycles; bead milling; high-speed homogenization; microwave and sonication. Sonication and bead milling proved to be the most efficient processes in cell disruption and release of biochemical compounds, however, when considering also the energy consumption, bead milling was the most efficient method. The results obtained in this thesis proved that photobiont extracts isolated from lichens are a promising source of bioactive compounds, thus confirming the high potential of these microorganisms in the biotechnological field. |
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