Characterization of Maillard-type lysozyme-galactomannan conjugate having immune-enhancing effects

•Lysozyme-galactomannan conjugate, LGC characterized with structural analysis.•High-molecular portion of LGC obtained by ion-exchange chromatography.•H-LGC improves immune activity via nitric oxide and cytokines.•The glycated site of conjugate is determined to be the Lys115 residue.•LGC solution shows shapes with a mean size of 337 nm in a monodispersion.

In the present study, lysozyme-galactomannan conjugate (LGC) was fractionated by ion-exchange chromatography, the immune activity of the fractions was confirmed, and a structural analysis of the glycoprotein was performed. A high-molecular-weight fraction of LGC (H-LGC), was characterized by using a method using matrix-assisted laser desorption/ionization time of flight mass spectrometry. The glycated site of H-LGC was determined to be the lysine (Lys)115 residue. In addition, about 1 mol of galactomannan (G) was linked to 1 mol of lysozyme (L) in LGC based on the binding weight ratio. Conjugation of L and G reduced the aggregation of particles, resulting in a monodispersion based on measurement of dynamic light scattering. LGC in solution showed heterogeneous shapes with a mean size of 337 nm. Therefore, we suggest that LGC improves the immune-enhancing activity as G conjugates the site of Lys115 on L, and provides higher solubility with reduced aggregation for the industrial use of LGC as a food constituent.