Protein particle and soluble protein structure in prepared soymilk

Systematically characterizing soymilk protein is important for understanding the formation of soymilk-related products and may be beneficial for enhancing the qualities of these products. Field emission scanning electron microscopy showed that soymilk protein could be divided into three categories: large (40–258 nm) and small (20–40 nm) stable protein particles and <20 nm soluble proteins. Regardless of soybean variety, the large protein particles contained lipoxygenase, γ-conglycinin, lectin, and Kunitz trypsin inhibitor as well as glycinin and β-conglycinin. These large protein particles were comprised of 40-nm protein aggregates (around 40 nm) formed by heat-dissociated soybean protein subunits. In addition, the small stable protein particles, which accounted for about 10% of soymilk protein, increased with β subunits of β-conglycinin while the soluble proteins (<20 nm) existed as monomers and oligomers of α′, α and acidic polypeptides.