Neutrons and Food 8 at MLZ

Seaweeds are increasingly recognised as sustainable, nutrient-dense candidates for future food systems, yet the mechanisms governing their gastrointestinal digestion remain unclear. Here, we show how the multiscale architecture of the red seaweed Porphyra umbilicalis (nori) governs protein bioaccessibility during digestion. Combining in vitro digestion with a multi-technique approach (microscopy, SAXS, SANS, X-ray holotomography), we tracked digestion-driven transformations from the nanoscale to the microscale. We found that Nori cell walls remain largely intact after gastric digestion, with a porphyran-rich dense matrix restricting pepsin access towards intracellular proteins. In contrast, intestinal conditions triggered pronounced cell wall disruption, enabling protein release and subsequent hydrolysis into peptides. Importantly, the released peptides and polysaccharides further interacted with bile salts, reshaping micellar assembly and suggesting an additional route by which seaweed components may modulate lipid digestion. Overall, our results demonstrate that protein–polysaccharide interactions in seaweeds not only control digestibility but also direct the self-assembly of digestion products. This structural–functional study provides a mechanistic basis for designing seaweed-based foods with improved nutritional performance and motivates future neutron-enabled studies linking the nanostructure of digestion to physiological outcomes, such as nutrient absorption and satiety