Improvement of anti-inflammatory activity of salmon muscle peptides by conjugation with alginate oligosaccharide and recovery of the active fraction using ampholyte-free isoelectric focusing

Chum salmon myofibrillar protein (Mf) digested by pepsin-trypsin (dMf) was conjugated to alginate oligosaccharide (AO) through the Maillard reaction between the lysine residues in the dMf and the reducing end-groups of AO. The dMf-AO conjugate strongly suppressed the production of inflammatory cytokines, particularly tumor necrosis factor-α and interleukin-6, in lipopolysaccharide-stimulated murine macrophages. The anti-inflammatory effect was enhanced with increasing amounts of AO bound to dMf through the Maillard reaction, and the subsequent process of the Maillard reaction was involved in the enhancement of the anti-inflammatory activity. AO-conjugated peptides, the major anti-inflammatory components contained in the dMf-AO conjugate, were successfully recovered using isoelectric focusing without the use of carrier ampholytes (autofocusing); they were effectively concentrated in acidic peptide fractions, with the negative charge of the carboxyl groups of AO contributing to this separation. In conclusion, the combined use of AO conjugation and autofocusing is a useful method for producing novel anti-inflammatory peptides from fish Mf.