Abstract:

Soybean is a good food resource of plant protein. Processing characteristics of soybean have been found to have a close relationship with the subunit composition of soy protein. Mutant soybean lines lacking α, α′ subunits or with lower ratio of β subunit were induced by γ-ray irradiation. China has a wide natural soybean germplasm variation in terms of cultivars with different properties including anti-disease, high oil content, high protein content, respectively. However, systematic evaluation of this occurrence on protein composition had been rarely investigated. The aim of this work was to identify the soybean germplasm variation with certain subunits absence therefore enable a deeper insight of its relationship with functional properties of soy protein.
Based on Laemmli’s(1970) method, the subunit composition of soy protein extracted from 1 624 Chinese soybean cultivars was analyzed by SDS-PAGE electrophoresis, and a simplified sample pre-treatment method was proposed(Fig.1). This qualitative analysis revealed that there were many native aberrant varieties having a lower proportion of or lacking A3, A5, γ, β-subunits in the 1624 soybean cultivars (Table 1). The SDS-PAGE patterns of some distinct soybean cultivars lacking certain subunit were shown(Fig.2-a, Fig.2-b). In addition, the result of Western Blot analysis proved the finding of a unique soybean cultivar lacking the β subunit in β-conglycinin(Fig.3, Fig.4), which was first reported among Chinese soybean cultivars. Thus it provides an essential material for further breeding experiments to improve the functional quality of soy protein.

Key words: Soy protein, Subunit lacking, β-subunit