Effects of pH-shifting combined with mild heating process on structural and functional properties of broad bean protein isolateS(BBPI) were investigated. The BBPI underwent heat treatment (25 ℃, 37 ℃ and 55 ℃) at pH=1.5 for 0, 1.5 h, 3.5 h, and 5.5 h, respectively, followed by refolding at neutral pH. Changes in its solubility, emulsification, sulfhydryl/total sulfhydryl content, UV and fluorescence spectrum, surface hydrophobicity, secondary structure content, and microstructure were explored. The results showed that both solubility and emulsification decreased first and then increased with time. The sulfhydryl content increased first and then decreased at 37 ℃ and 55 ℃, respectively, and it remained almost unchanged at 25 ℃. At 37 ℃, total sulfhydryl content increased first and decreased rapidly. It remained almost stable at the beginning and reduced at 25 ℃ and 55 ℃, respectively. UV and fluorescence spectroscopy revealed that most of the tryptophan(Trp) residues were wrapped and located mainly in the hydrophobic area in the inner core of BBPI at 25 ℃. However, the Trp residues were found unfolded at 37 ℃. Surface hydrophobicity of BBPI increased first and then decreased at 25 ℃ and 37 ℃, respectively, but it increased and then fluctuated at 55 ℃. As temperature increasing, the α-helical and β-sheet of BBPI gradually transformed into β-turn and random coil, and the particles were spherical agglomerates with average diameter around 80-130 nm. Therefore, it was concluded that structural and functional properties of BBPI could be changed via pH-shifting combined with mild heating process to some extent.
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