Physicochemical dynamic changes and differences of κ-carrageenan in different vehicles (aqueous and casein solution) during in vitro gastrointestinal digestion

To better understand the inflammatory mechanism of carrageenan in the gastrointestinal tract, the differences of κ-carrageenan (κ-CGN) in different vehicles (aqueous and casein solutions) and the physicochemical changes were investigated, including reducing sugar content, sulfate content, structural and conformational changes during in vitro digestion. Our results revealed that the reducing sugar content and FTIR characteristic peaks of κ-CGN hardly changed indicating the consistency of chemical structure during digestion. The exposed sulfate group content of κ-CGN solution in the digestive juice showed a downward trend and its physical conformation experienced coil-helix-coil transition due to the existence of pH and various electrolytes. While κ-CGN in κ-carrageenan-casein (κ-CC) solution maintained a stable helical structure due to hydrogen bonds and electrostatic interactions between κ-CGN and casein. Additionally, the exposed sulfate group content of κ-CC solution was always lower than κ-CGN solution. Overall, the presence of casein reduced the exposure of sulfate groups and improved the conformational stability of κ-CGN. Therefore, the differences of the conformation and exposed sulfate group content of CGN in different vehicles might contribute to the different inflammatory effects in the gastrointestinal tract, which has guiding significance to the safe consumption of CGN.