Discovery of D-galactitol in Laminaria japonica and its role in enhancing moisture retention and texture of gluten products

Marine macroalgae are rich sources of bioactive substances with potential moisturizing effects. To screen for natural moisturizing agents, seven macroalgal species were extracted with methanol and further subjected to solvent partitioning. The ethyl acetate extracts of Grateloupia furcata and Sargassum sp., and the n-butanol and aqueous extracts of Laminaria japonica exhibited remarkable hygroscopic and moisturizing activities, comparable to or exceeding those of sorbitol and glycerol. Bioactivity-guided fractionation of the aqueous extract of L. japonica was further fractionated via silica gel chromatography to yield three subfractions (AD1–AD3), among which AD1 showed the strongest activities, superior to or close to sodium alginate, sorbitol and glycerol. Enriched in magnesium, sodium, iron and copper, AD1 improved the moisturizing effect and quality of scissor-cut noodles significantly. Combined IR, ESI–MS and NMR analyses identified AD1 as D-galactitol, isolated and characterized from Laminaria japonica (marine macroalgae) for the first time. Molecular docking analysis revealed that D-galactitol interacts specifically with gluten proteins, modulating the gluten network to enhance noodle moisture retention and elasticity, thus improving textural quality. This study first isolates and characterizes D-galactitol from L. japonica as a marine-derived natural humectant and elucidates its moisturizing mechanism, providing preliminary evidence for its potential application as a food-grade humectant in the food and cosmetic industries.