Preparation process optimization and structural characterization of rapeseed peptide-ferrous chelate

To enhance the utilization value of rapeseed protein and develop chelates with high iron-binding capacity, rapeseed protein and ferrous chloride tetrahydrate were used as raw materials to explore the impact of six proteases on the iron-binding capacity of rapeseed peptide (RP) and rapeseed peptide-ferrous chelates (RP-Fe). Firstly, the effect of 6 types of proteases (alkaline, flavoring, trypsin, Protease M, neutral, and papain) on the iron-binding ability of RP-Fe was investigated, and then the chelation process was optimized through single-factor and orthogonal experiments. Finally, the structures of RP and RP-Fe were characterized using scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and fourier transform infrared spectroscopy (FTIR). The results of protease selection indicated that the RP-Fe prepared by Protease M for 3 h exhibited the strongest iron-binding capacity. The optimal preparation conditions were a peptide-to-iron mass ratio of 2∶1, a peptide concentration of 60 mg/mL, a temperature of 30 ℃, a reaction time of 50 min, and a pH of 7.0. Under these conditions, the iron-binding capacity of the chelates reached (120.40±0.59) mg/g. Compared to rapeseed peptides, the chelates exhibited smaller particles with rougher surfaces, and an absorption peak for Fe elements appeared in the energy dispersive spectrum. Additionally, the particle size of the latter is significantly smaller than the former. EDS showed that there was no signal peak of iron element in RP, while there were three in RP-Fe. FTIR showed that the positions and intensities of the absorption peaks for carbonyl, amino, and carboxyl groups changed significantly after the chelation. The research findings demonstrated that the chelation effect between rapeseed peptides and ferrous ions was satisfactory, with amino, carbonyl, and carboxyl groups serving as the primary reactive functional groups.