Anthocyanins, the pigments that paint blueberries, blackcurrants, and purple sweet potatoes in vivid reds and blues, are among the most celebrated antioxidants in the plant kingdom. Decades of research have linked these water-soluble flavonoids to anti-inflammatory and protective effects, making them prized candidates for functional foods. Yet there is a stubborn problem: the human digestive tract is a hostile place for them. Stomach acid, fluctuating pH, and degrading enzymes destroy most anthocyanins before they ever reach the small intestine, where absorption actually occurs. The result is that the bioavailability of these compounds is dramatically reduced, and much of the nutritional promise of anthocyanin-rich foods is lost between the mouth and the bloodstream.
Food scientists have long tried to solve this with encapsulation, wrapping sensitive molecules in protective carriers that shield them in the stomach and release them further down the line. Gel-based delivery systems have emerged as a leading strategy, but most of them share a common flaw. They typically rely on differential swelling: the gel swells more in the intestine than in the stomach, allowing some cargo to escape. The problem is that the matrix itself often survives the intestinal stage largely intact, trapping a substantial fraction of the anthocyanins inside. Previous systems built from gelatin and gellan gum, or from peptides and whey protein isolate, achieved respectable but incomplete release, leaving a meaningful portion of the payload locked away in a structure that never fully fell apart.
A research team led by Wenjun Li and colleagues has now reported a solution in Food Chemistry: X that hinges on an unusual ingredient from the sea: fucoidan, a sulfated polysaccharide extracted from brown seaweeds. The key insight lies in electrostatics. In an earlier study, the group had built gelatin-pectin gels in which pectin’s carboxyl groups, with a pKa of roughly 3.5, flip from mostly uncharged in the acidic stomach to strongly negatively charged in the near-neutral intestine. That charge shift drove electrostatic repulsion and partial network collapse, releasing about 80 percent of the encapsulated anthocyanins. Impressive, but not complete. Fucoidan offered something better: its sulfate ester groups carry pKa values of only about 0.5 to 2.0, meaning they remain aggressively anionic across virtually the entire gastrointestinal pH range.
The team’s hypothesis was elegant. Gelatin, a protein derived from collagen, carries a positive charge under strongly acidic conditions. Pair it with fucoidan in the stomach, and the opposite charges attract, compensating one another and locking the network into a stable, self-supporting gel. Shift to intestinal pH, however, and fucoidan’s sulfate groups become massively negative while gelatin’s positive charge fades. The once-balanced composite turns strongly anionic, electrostatic repulsion takes over, and the network destabilizes, potentially disintegrating so thoroughly that nearly all of the anthocyanins are freed. To test this, the researchers prepared a systematic matrix of 25 formulations, varying total solid content from 2 to 10 percent and the gelatin-to-fucoidan mass ratio from 9:1 down to 5:5.
The characterization work revealed clear rules of composition. Rheological measurements showed that all gel-forming formulations behaved as true elastic gels, with the storage modulus exceeding the loss modulus, and that stiffness climbed steadily with solid content. Hardness testing with a texture analyzer confirmed the same trend: more solids meant more internal crosslinking and greater mechanical strength. Scanning electron microscopy of a representative 10 percent gel revealed the porous, interconnected three-dimensional architecture that gives hydrogels their capacity to harbor small molecules. Not every combination worked, however. The 5:5 gelatin-fucoidan mixtures failed to form self-supporting gels at any solid content, and the 2 percent formulations were too soft to measure reliably, establishing that a sufficient gelatin fraction is essential to build the continuous network in the first place.
Encapsulation performance was striking across the board. Every stable gel-forming formulation captured more than 95 percent of the added anthocyanins, with the best result, 98.77 percent, achieved by the 10 percent gel at a 6:4 ratio. Fluorescence microscopy showed the pigments distributed uniformly throughout the matrix with no aggregation. Storage tests over 14 days demonstrated that encapsulated anthocyanins retained far more of their color and content than free anthocyanins, particularly under light exposure, where unprotected pigments degrade fastest. The gel was not just a delivery vehicle but also a preservative, extending the shelf-life stability of the compounds it carried.
The electrostatic story played out exactly as predicted. Zeta potential measurements showed that at pH 1.5, gelatin carried a positive charge of about +7 millivolts while fucoidan was mildly negative, and the composite sat near neutral at +2 millivolts, the signature of charge compensation. At pH 6.8, fucoidan plunged to −42.2 millivolts and the composite shifted to −20.6 millivolts, a distinctly anionic state primed for repulsion-driven collapse. Correspondingly, in simulated gastric fluid the gels swelled moderately but held their macroscopic shape for the full two-hour digestion, while in simulated intestinal fluid they dissolved dramatically, with the softest formulations vanishing within an hour. Control experiments at body temperature confirmed that the 10 percent composite gel remained self-supporting in gastric conditions yet disintegrated in intestinal fluid, showing the response was not merely an artifact of gelatin’s thermal softening.
The release data delivered the headline result. The standout formulation, containing 10 percent solids at an 8:2 gelatin-to-fucoidan ratio, leaked only 3.50 percent of its anthocyanins during the gastric stage, then released 99.94 percent of the total payload after intestinal exposure, essentially complete liberation within experimental error. Neighboring high-solid formulations at 9:1 and 7:3 ratios performed nearly as well, at 99.11 and 98.08 percent. For context, the team’s earlier gelatin-pectin system managed 87.87 percent intestinal release with 10.70 percent gastric leakage, and a dual-crosslinked apricot polysaccharide hydrogel reached about 87 percent cumulative release. The new system outperformed both benchmarks on gastric retention and intestinal delivery simultaneously, resolving the trade-off that had limited earlier designs.
Kinetic modeling added mechanistic texture to the findings. Fitting the release profile to five standard models showed that the Logistic model described the sigmoidal, stage-dependent behavior best, with an R-squared of 0.998, capturing the quiet gastric phase, the sharp surge after the pH transition, and the final plateau. The Ritger-Peppas exponent of about 1.07, though a weaker fit, pointed toward release governed by structural changes in the matrix rather than simple diffusion, consistent with the visual evidence of network disintegration coinciding with the release surge. Together, the kinetics and microscopy painted a coherent picture: anthocyanin liberation is driven not by passive swelling but by the active, pH-triggered dismantling of the gel network itself.
Beyond the immediate result, the study offers a design framework with broader implications. It demonstrates that the responsive element of a delivery gel can be tuned by choosing polysaccharides with different ionizable group chemistries, and that sulfate-rich marine polysaccharides deserve a central place in that toolkit. The composition rules matter too: more fucoidan is not automatically better, because the network-forming capacity of gelatin and the electrostatic responsiveness of fucoidan must be balanced. The authors note that the roles of digestive enzymes, bile components, and intestinal ions in modulating release still merit targeted investigation before such systems reach real foods. But the principle is now established: with the right polymer pairing and the right recipe, a food-grade gel can guard delicate plant pigments through the stomach’s acid bath and then dissolve almost completely where the body can actually use them.
Subject of Research: pH-responsive gelatin-fucoidan composite hydrogels for gastrointestinal delivery of anthocyanins
Article Title: Composition-guided design of Gelatin-fucoidan composite gels for gastric anthocyanin retention and intestinal release
Article References: Li, W., Li, J., Zeng, Q., Chen, W., Chen, X., Huang, Y., & Yang, W. (2026). Composition-guided design of Gelatin-fucoidan composite gels for gastric anthocyanin retention and intestinal release. Food Chemistry: X, 39, Article 104538. https://doi.org/10.1016/j.fochx.2026.104538
Image Credits: AI Generated
DOI: 10.1016/j.fochx.2026.104538
Keywords: anthocyanins, fucoidan, gelatin, hydrogels, drug delivery, bioavailability, pH-responsive, electrostatics, food chemistry, encapsulation, marine polysaccharides, simulated digestion
Neil Sanderson. (October 4, 2026). Sulfated Seaweed Polymer Helps Gels Protect Anthocyanins Until the Gut. Scienmag.
