Publicação
Green strategies for the valorization of algae’s polysaccharides for food applications
| Resumo: | This thesis explores new approaches to valorize algae carbohydrates. Due to their higher carbohydrate content and recognized market value, red seaweeds (from the Gracilaria, Gelidium, Pterocladiella, and Porphyra genus) were used for process optimization. Sequential treatments using cold water (aimed at phycobiliprotein removal), ethanol (aimed at pigment removal), and mild alkali extraction (aimed at protein removal) were evaluated in several combinations. While the optimal sequence varies for each biomass, the recovery of an additional valuable fraction without compromising hydrocolloid texturizing properties was always achieved. Using Gelidium as a model seaweed (due to its higher-grade agar), the extraction of agar using autohydrolysis was evaluated. This methodology is based on the properties of water in the subcritical state (at high temperatures and pressures). Using it, it was possible to decrease the extraction time from hours (using the conventional boiling water) to minutes, without losing efficiency or affecting agar’s texturizing properties. Moreover, it was demonstrated that the outcome can be modulated by the severity factor (a calculation that considers the treatment’s temperature at each time point), with different time and temperature binomials of the same severity yielding similar outcomes. Due to the market for Gelidium seaweeds (and the subsequent residues produced from their processing), the valorization of their industrial agar-extraction residues was also assessed. Hydrothermal treatments were tailored towards carbohydrate (residual agar or oligosaccharides) and protein recovery. Sequential processing ensured that recovery of both carbohydrate and protein fractions was possible. Thus, a cascading biorefinery approach aiming at maximum functionality and minimal waste was proposed. Considering the promising results obtained, the approach was applied to the microalgae Phaeodactylum tricornutum, due to its rheological properties and bioactivity, and carbohydrate-protein extracts with both bioactivity and texturizing properties were achieved. The prebiotic effect of the oligosaccharide-rich fractions produced during the work was assessed, with all extracts showing the ability to be fermented by pure probiotics. Selected samples were fermented in vitro using fecal samples, and their gut microbiota modulation and production of beneficial short-chain fatty acids were validated. Overall, this work established a sustainable strategy for the valorization of algae fractions, demonstrating their potential for nutraceutical and texturizing applications. |
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| Autores principais: | Dias, Joana Sofia Gomes |
| Assunto: | Bioactivity Cascading biorefinery Hydrocolloids Prebiotics Texturizing Bioatividade Biorefinaria Hidrocolóides Prebióticos Texturizantes Ciências Agrárias::Biotecnologia Agrária e Alimentar |
| Ano: | 2026 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso embargado |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | This thesis explores new approaches to valorize algae carbohydrates. Due to their higher carbohydrate content and recognized market value, red seaweeds (from the Gracilaria, Gelidium, Pterocladiella, and Porphyra genus) were used for process optimization. Sequential treatments using cold water (aimed at phycobiliprotein removal), ethanol (aimed at pigment removal), and mild alkali extraction (aimed at protein removal) were evaluated in several combinations. While the optimal sequence varies for each biomass, the recovery of an additional valuable fraction without compromising hydrocolloid texturizing properties was always achieved. Using Gelidium as a model seaweed (due to its higher-grade agar), the extraction of agar using autohydrolysis was evaluated. This methodology is based on the properties of water in the subcritical state (at high temperatures and pressures). Using it, it was possible to decrease the extraction time from hours (using the conventional boiling water) to minutes, without losing efficiency or affecting agar’s texturizing properties. Moreover, it was demonstrated that the outcome can be modulated by the severity factor (a calculation that considers the treatment’s temperature at each time point), with different time and temperature binomials of the same severity yielding similar outcomes. Due to the market for Gelidium seaweeds (and the subsequent residues produced from their processing), the valorization of their industrial agar-extraction residues was also assessed. Hydrothermal treatments were tailored towards carbohydrate (residual agar or oligosaccharides) and protein recovery. Sequential processing ensured that recovery of both carbohydrate and protein fractions was possible. Thus, a cascading biorefinery approach aiming at maximum functionality and minimal waste was proposed. Considering the promising results obtained, the approach was applied to the microalgae Phaeodactylum tricornutum, due to its rheological properties and bioactivity, and carbohydrate-protein extracts with both bioactivity and texturizing properties were achieved. The prebiotic effect of the oligosaccharide-rich fractions produced during the work was assessed, with all extracts showing the ability to be fermented by pure probiotics. Selected samples were fermented in vitro using fecal samples, and their gut microbiota modulation and production of beneficial short-chain fatty acids were validated. Overall, this work established a sustainable strategy for the valorization of algae fractions, demonstrating their potential for nutraceutical and texturizing applications. |
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