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Abstract The intestinal barrier is critical in maintaining gut homeostasis and host health. The intestinal barrier dysfunction contributes to intestinal and systemic diseases like inflammatory bowel disease, colorectal cancer, and metabolic syndromes. This review summarizes the physicochemical properties of three main kinds of brown seaweed polysaccharides (BSP), laminarin, fucoidan, and alginate, along with their absorption and metabolism in the intestine and their effects on the intestinal barrier. The physicochemical properties of BSP were closely related to their beneficial effects on intestinal health. BSP were not digested directly in the upper gastrointestinal tract but could be utilized through fermentation by the gut microbiota. BSP kept the integrity of intestinal epithelium by ameliorating intestinal oxidative stress through the nuclear factor erythroid 2‐related factor 2 signaling pathway. They also reduced tight junction dysfunction and intestinal permeability and increased the expression of mucins. Moreover, BSP regulated the composition and abundance of gut microbiota and promoted the production of beneficial metabolites such as short‐chain fatty acids. This review will help to understand the gut health‐promoting functions of the natural compounds derived from brown seaweed and offer a new perspective on intestinal disease prevention and therapy with high effectiveness and safety.

Abstract An alginate (named P1) prepared from Sargassum fusiforme has been proven to have significant anti‐photoaging activity in our previous study. In this study, alginate lyase was used to obtain P1 hydrolysates with different molecular weights, and their structural characteristics and anti‐photoaging activity were compared. Results showed that alginate lyases could rapidly degrade the molecular weight of P1 and slightly changed its chemical composition. Fourier transform infrared spectra indicated that alginate lyase treatment did not change the main functional groups of P1. Moreover, the inhibitory effects of P1 on MMPs (MMP‐1, MMP‐3 and MMP‐9) and reactive oxygen species were also improved after hydrolyzed with alginate lyase, especially sample A‐30 (hydrolysis for 30 min). Methylation and nuclear magnetic resonance results indicated that the main chain of A‐30 was →4)‐β‐ManA‐(1→4)‐α‐GulA‐(1→4)‐β‐ManA‐(1→4)‐β‐ManA‐(1→4)‐α‐GulA‐(1→4)‐β‐ManA‐(1→3, 4)‐β‐ManA‐(1→, with the end group of α‐Fucp‐(1→ attached to the O‐3 position of →3, 4)‐β‐ManA‐(1→ on the side chain. It indicated that alginate lyase did not change the backbone of P1 but decreased the molecular or degree of polymerization at 30 min of hydrolysis. This is the first report on the anti‐photoaging activity of alginate hydrolysates. The results will provide effective theoretical support for improving the utilization and promoting the application of S. fusiforme.