Evolution of the structure and rheology of processed seaweed Ulva spp. during in vitro digestion

Seaweed is a sustainable and nutrient-rich food source, but its complex cell wall architecture can physically shield its components from digestion, potentially limiting their release and utilisation. This study investigated how mechanical (blending) and thermal (40-100 °C) processing affect the structure, rheology, and digestive behaviour of Ulva spp. dispersions. Processing modulated particle size, softness, and polysaccharide solubilisation, influencing the viscosity and viscoelastic properties of the dispersions. During in vitro digestion, gastric viscosity increased over time for all samples, driven by particle swelling, while intestinal viscosity was lower and stable, except in the 100 ^°C-treated sample, where it increased, suggesting greater release of soluble components. Small-angle X-ray scattering (SAXS) indicated larger nanostructural disruption of the cell wall and release of cell wall components, potentially ulvan, in the 100 °C-treated sample, which might lead to enhanced digestibility. Large unheated particles (D_{[3, 2]} ≈100 μm) showed limited breakdown, whereas thermally treated particles exhibited greater degradation during simulated digestion. These findings demonstrate that processing governs both physical structure and digestive performance, enabling the design of seaweed-based foods with improved functionality.