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