Abstract: The effects of microfluidization applied at different pressures (0, 42.5, 89.0, 123.5, 152.0 and 175.5 MPa) on the structure and solubility of black bean protein isolate (BBPI) from wild black beans were studied. The results showed that microfluidization enhanced the hydrophobic interaction between wild BBPI molecules and caused breakdown of unstable aggregates into soluble proteins. However, high shearing strength at pressure exceeding 123.5 MPa resulted in reaggregation of the soluble proteins. The emulsifying activity of BBPI increased initially and then decreased with increasing pressure, while the emulsion stability did not change significantly (P > 0.05). Raman spectroscopy analysis showed that compared with native BBPI, the contents of α-helical and β-sheet decreased in all simples subjected to microfluidization. Microfluidization resulted in partial unfolding of the proteins and exposure of tryptophan residues on the protein surface as demonstrated by a decrease in the intensity of tryptophan band at 760 cm-1, but it significantly increased the intensity of tyrosine band, indicating that the microenvironment around tyrosine residues was altered. The Raman intensity increased as the homogenization pressure increased, resulting in conformational transformation of disulfide bond from t-g-t to g-g-t.

Key words: microfluidization, wild black bean protein, solubility, surface hydrophobicity, emulsification, Raman spectroscopy