Ultrasound-assisted extraction (UAE) of polyphenols from the brown seaweeds Ascophyllum nodosum leaves a solid phase where alginates can be extracted. This study characterizes alginates extracted after the UAE process, with and without an intermediate drying stage at different temperatures (50 and 90 °C) producing sequentially two bioactive compounds from a unique raw material. FT-IR and ¹H NMR analyses showed the high purity of alginates with features in the range of commercial alginates. Drying at high temperature decreased average block length and viscosity average molecular weight (M_v) of alginate from 428 to 133 kg/mol. Steady-shear curves (shear-thinning behaviour) and viscoelasticity (liquid like character) features depended clearly on M_v. Solutions of alginates with high M_v were more viscous and the elastic character was more relevant. Cox-Merz rule was only accomplished within the semi-dilute regimes of alginate concentration. Tested process conditions allow the production of alginates with different properties.

Seaweeds have gained considerable attention in recent years due to their potential health benefits and high contents of bioactive compounds. This review focuses on the exploration of seaweed’s health-promoting properties, with particular emphasis on phlorotannins, a class of bioactive compounds known for their antioxidant and antidiabetic properties. Various novel and ecofriendly extraction methods, including solid–liquid extraction, ultrasound-assisted extraction, and microwave-assisted extraction are examined for their effectiveness in isolating phlorotannins. The chemical structure and isolation of phlorotannins are discussed, along with methods for their characterization, such as spectrophotometry, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and chromatography. Special attention is given to the antioxidant activity of phlorotannins. The inhibitory capacities of polyphenols, specifically phlorotannins from Ascophyllum nodosum against digestive enzymes, such as α-amylase and α-glucosidase, are explored. The results suggest that polyphenols from Ascophyllum nodosum seaweed hold significant potential as enzyme inhibitors, although the inhibitory activity may vary depending on the extraction conditions and the specific enzyme involved. In conclusion, seaweed exhibits great potential as a functional food ingredient for promoting health and preventing chronic diseases. Overall, this review aims to condense a comprehensive collection of high-yield, low-cost, and ecofriendly extraction methods for obtaining phlorotannins with remarkable antioxidant and antidiabetic capacities.

Aqueous extracts fromAscophyllum nodosumbrown edible seaweeds were obtained after continuous ultrasound-assisted extraction. The effect of sonication time (from 2 to 6 min), sonication amplitude (from 80 to 100%) and solvent-solid ratio (from 20 to 40 g water g⁻¹dried seaweed) on the extracts features was studied employing a Box-Behnken experimental design. Extracts were characterised by polyphenols, carbohydrate and uronic acid content. Response surface method (by means of a quadratic model) was successfully employed to relate chemical composition of extracts and operation conditions. Optimal experimental conditions were established to obtain maximal polyphenols content and several polyphenols-carbohydrates ratios together with the conditions that minimise energy consumption per extracted polyphenols amount relationship. Antioxidant capacities of extracts were measured employing different methods (DPPH, FRAP and ABTS). Positive linear correlations between antioxidant activity and total polyphenols content were established.