Globin is an edible protein that is obtained in large quantity from animal blood. It can be used as an ingredient in a variety of meat products. However, globin showed a rather low solubility at neutral pH and little advantage compared with other proteins used in the food industry. The effective use of latent materials is an important research area in food science. This study succeeds in improving globin's functional properties and explaining the mechanism of gel formation. The hydrolysis of globin was performed with 0.8 M citric acid. The globin hydrolysates showed eight bands by tricine−SDS−PAGE having molecular masses that ranged from 5000 to 15 000 Da. The results of gel filtration chromatography indicated that the large aggregates were formed easily in the case of the globin hydrolysates. Physicochemical properties of aggregates of globin hydrolysates were studied by light scattering measurement and transmission electron microscope. It is clear that the aggregates were composed of two kinds of polypeptides, one of which, the β-chain, originated from the native globin and another, β-1, originated from the β-chain by cleavage between 99 (Asp) and 100 (Pro) of the β-chain through noncovalent bonding. By comparison with the position of standard protein (thyroglobulin, MW 669 000 Da), the molecular mass of the aggregate was estimated as above 700 000 Da. The aggregates of globin hydrolysate in solution approximated the thin rod-shaped model and had lengths of 130−140 nm by light scattering measurement. Electron micrography also showed the aggregates to consist of the thin rod aggregates. The molecular mass of the aggregates was determined to be 870 000 Da by light scattering measurement, indicating that the aggregate consists of 33−34 units because each unit was in the ratio of 1:1 complex of β-chain and β-1 with molecular masses of 16 000 and 10 900 Da, respectively. Keywords: Globin; globin hydrolysates; aggregates; light scattering; tricine−SDS−PAGE

Globin is an edible protein in a large quantity from animal blood. However, globin shows a rather low solubility at neutral pH and little advantage in comparision with other proteins applied to the food industry. To improve its functional properties and to make clear the mechanism of gel formation, the hydrolysis of globin was performed with 0.8 M citric acid. The peptide α-1 was obtained by cleavage of the peptide bond between Asp-94 and Pro-95 in the α-chain of globin with 0.8 M citric acid. Physicochemical properties and structural characterization of peptide α-1 of globin hydrolysates were studied by amino acid sequence analysis, hydrophobic interaction chromatography, and circular dichroism (CD) spectra. The peptide α-1 was very highly hydrophilic on hydrophobic chromatography. The concentration dependence of peptide α-1 indicated the dissociation and association behaviors analyzed by a light scattering method. Circular dichroism spectra showed that the content of the α-helix and β-sheet structures of peptide α-1 were very different from the intact α-chain. We have also found that peptide α-1 played a role in transformation of aggregates of globin hydrolysates to gel. These results suggest that peptide α-1 acts as a cross-linker between the aggregate of globin hydrolysates through the transformation process of gel. Keywords: Globin; globin hydrolysates; peptide α-1; CD spectra

To investigate the aggregation process of globin hydrolysates treated with 0.8 M citric acid and the transformation process of the resulting aggregates to gel mediated by addition of peptide α-1, the interaction between the aggregates of the globin hydrolysate and peptide α-1 was examined through the determination variation in diffusion coefficient D with reaction time by quasi-elastic light scattering technique. The results revealed that in the case of the aggregates of the globin hydrolysate alone the diffusion coefficient D showed no change, but in the case of the mixture containing the aggregates of the globin hydrolysates and peptide α-1 (the mixing ratio is 7:3, and the final total concentration is 20 mg/mL) the diffusion coefficient decreased sharply with reaction time. On the basis of these results a gelation model for the globin hydrolysates was presented as follows:  initially, 8 molecules of the randomly coiled peptide α-1 are involved in the initial complex of the globin hydrolysate and peptide α-1; next, the cross-linked structure was constructed by the interaction between peptide α-1 and the rod-shaped aggregates; and then a network structure was formed, and a gel was finally formed. Keywords: Globin; globin hydrolysates; aggregates; peptide α-1; quasi-elastic light scattering; circular dichroism