| Summary: | Global problems including lack of food, clean water, and energy, are worsening, especially in aquaculture due to overfishing damaging ecosystems. Meanwhile, meeting a rising seafood demand while wild fisheries decline is a challenge. However, microalgae, highly adaptable and diverse microorganisms, could provide sustainable feed solutions, but to tap into their potential, it is necessary to optimize biorefinery processing methodologies. In this thesis, a novel microalga, Raphidonema monicae (previously known as Koliella antarctica), was selected to produce fractions enriched in high-value compounds. By combining high-pressure homogenization and enzymatic hydrolysis techniques, a methodology comprised of 1 cycle of HPH at 1068 bars followed by a 1h alcalase treatment at 5% concentration (w/w), 50 ºC, pH 8 was optimized, achieving 71% disruption efficiency. Using fractionation methodologies including micro and ultrafiltration, pH shifting and ethanolic extractions, six fractions were produced, found to be enriched in high-value compounds including PUFA, such as eicosapentaenoic acid (EPA), arachidonic acid (ARA), linoleic acid (LA), α-linolenic acid (ALA), and γ-linolenic acid (GLA), and certain bioactive pigments including lutein, neoxanthin, zeaxanthin and β-carotenes. These, and non-treated and disrupted fractions of R. monicae, to a total of 9 fractions, were evaluated in their potential to improve fish health by assessing the transcriptional response of genes related to the epithelial integrity (OCL and TJP2), antioxidant capacity (GPx and CAT) and immunostimulation (COX2 and IL1B) in the intestine. While these fractions were found to have no significant influence on the transcription response, some up and down-regulatory expression trends were noticed regarding the antioxidant and immunostimulation genes, suggesting the fractions potentially contributed to the protection of the intestine. Further studies are however needed, to fully ascertain if these fractions hold any potential as feed ingredients for the ...
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