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- Zero-Waste Hydrogel Design via Integral Biomass Valorization of Protein-Rich Spirulina MicroalgaePublication . Aquino, Leandro Lima ; Silva-Pituco, Samara C.; Hernandez-Sosa, Alejandro; Ramalhosa, Elsa; Hernandez, Rebeca; Colla, Eliane; Santamaria-Echart, Arantzazu; Barreiro, FilomenaInterest in alternative protein sources has grown, with Spirulina, a microalga belonging to the genus Limnospira (formerly Arthrospira), emerging as a key option. Guided by sustainability principles, this study explored the gelling capacity and hydrogel-forming properties of integral Spirulina biomass (SpB), targeting applications in structured foods. Two experimental designs (DoE) were employed. One to identify key factors influencing hydrogel formation, and another to optimize the formulation (22 wt%, pH 5.6, thermal gelation at 90 °C). Syneresis analysis revealed that high SpB hydrogels experienced less water loss, with the 22% sample losing just 2.51% after 14 days, due to its dense, particulate morphology as observed by means of scanning electron microscopy. Rheological analysis confirmed the optimized formulation’s superior mechanical properties, with a storage modulus (G′) 24-times higher than the low concentration reference sample (~1890 Pa), remaining dominant over the loss modulus (G″) (G′ > G″) across the analysed frequency range, corroborating a strong elastic behaviour. Although the recovery tests showed partial recovery (27.1%) after high shear, the high residual stiffness (≈515 Pa) confirmed the material’s ability to maintain its shape. These results enabled successful 3D printing tests with the optimized hydrogel, pointing out its potential for innovative food applications in structured food design.
- Chitosan-xanthan gum-based hydrogels loaded with essential oil distillation by-products of Aloysia citrodora Paláu for antimicrobial systemsPublication . Almeida, Heloísa H.S.; Santamaria-Echart, Arantzazu; Amaral, Joana S.; Aquino, Leandro Lima ; Rodrigues, Alírio E.; Barreiro, FilomenaHydrogels, 3D hydrophilic networks formed by oppositely charged biopolymers like chitosan and xanthan gum, offer a safe, non-toxic, and biocompatible option for delivery applications. Essential oil (EO) by-products, such as hydrosols and wastewater, are sources of antioxidant and antimicrobial compounds, but their high dilution can limit direct applications. In this context, this work focused on the development of hydrogels via electrostatic complexation incorporating hydrosol and wastewater by-products from the steam distillation of Aloysia citrodora Palau, using a two-stage approach: (a) initial loading during hydrogel formation and (b) subsequent reloading of the hydrogels to further enhance the concentration of bioactive compounds. The effect of pH (4, 7, and 11) on polymer complexation was evaluated, as it influences polymer-polymer and polymer-bioactive compound interactions by modifying the protonation and deprotonation states of their functional groups. This effect was evident in swelling, release kinetics, morphology, and rheological properties. Fourier-transform infrared (FTIR) analysis confirmed the successful formation of the polymer complex. Neutral pH hydrogels showed the highest hydrosol entrapment (70.3%) and were selected as the most promising systems. Biological characterisation showed that the reloading process enhanced bioactivity. Wastewater-load-reload improved antioxidant capacity, driven by the high phenolic content. Moreover, hydrosol-loaded-reload systems exhibited antimicrobial activity, with bactericidal effects against Staphylococcus aureus and Escherichia coli, outperforming both unloaded and loaded systems. These findings highlight the potential of loading and reloading steps to valorise EO by-products, producing sustainable, functional hydrogels with high bioactivity, suitable for food, pharmaceutical, medical, and biotechnological applications.