Low-molecular-weight carrageenan prepared by photocatalysis-freeze-thaw circle and its in vivo distribution after oral administration

Low-molecular-weight carrageenan has attracted great attention in the food and medical industries due to its excellent solubility and diverse biological activities. However, the development of environmentally friendly methods for low-molecular-weight carrageenan production is still in great need. In the present study, a photocatalysis-freeze-thaw circle degradation method of κ-carrageenan was developed based on its two-phase properties after freezing and thawing. Interestingly, the addition of KCl with the ability to enhance the gel strength could lead to the molecular weight decrease of the prepared low-molecular-weight carrageenan whose relative molecular weight could reduce to ≤2.8 kDa. Moreover, FT-IR, ESI-MS n , NMR, and TEM analysis results showed that the photocatalysis-freeze-thaw circle method could separate the degraded low-molecular-weight carrageenan in time to avoid overreaction during the reaction process, which could fully protect the sulfate groups of low-molecular-weight carrageenan from destruction and produce less by-products. In addition, the digestion and distribution of low-molecular-weight carrageenan in vivo were tracked after fluorescent labeling, and the results demonstrated that low-molecular-weight carrageenan could enter the liver and kidney after oral administration. Thus, the present study demonstrated a novel method to prepare low-molecular-weight carrageenan and revealed in vivo distribution after oral administration.