Purification and Characterisation of κ-Carrageenan Oligosaccharides Prepared by κ-Carrageenase from Thalassospira sp. Fjfst-332

κ-Carrageenan oligosaccharides (KCOs) are promising agents for treating inflammatory diseases. However, the lack of purification and structural elucidation of KCOs has limited structure-function evaluation. In this study, using a system coupling medium pressure liquid chromatography (MPLC) with an evaporative light scattering detector (ELSD), four types of KCOs were separated. The total yield of the four KCO powders was ∼5.02% after purification (KCOs/κ-carrageenan, w/w). Their structural identities were characterised by ESI-MS, CID-MS/MS and NMR, as κ-neocarrabiose (α-DA-1,3-G4Srα/β), κ-neocarratetraose (α-DA-1,3-β-G4S-1,4-α-DA-1,3-G4Srα/β), κ-neocarrahexaose (α-DA-1,3-β-G4S-1,4-α-DA-1,3-β-G4S-1,4-α-DA-1,3-G4Srα/β) and heterozygous κ/ι-neocarrahexaose (α-DA/DA2S-1,3-β-G4S-1,4-α-DA-1,3-β-G4S-1,4-α-DA-1,3-G4Srα/β). KCOs showed no cytotoxicity in RAW264.7 macrophages, and the anti-inflammatory activity was closely correlated with the degree of polymerisation and the number of sulfated groups. κ/ι-Neocarrahexaose exhibited the highest inhibition of ROS (Reactive Oxygen Species) production in LPS-induced RAW264.7 macrophages. The MPLC-ELSD system provides a platform for large-scale fabrication of purified KCOs and affords a route to these compounds that may regulate immune defense.