Fluorescence Quenching Properties of Vegetable Protein Caused by Potassium Sorbate with Non-covalent Bonding Interactions

The interaction between potassium sorbate(PSS) and soy protein isolate(SPI) or wheat gluten(WG) under different temperatures in solution was investigated by fluorescence spectroscopy. The quenching mechanism was analyzed referring to PSS against the fluorescence of the vegetable protein. The apparent binding constants and the binding sites were also determined simultaneously based on the fluorescence. The experimental results clearly indicated that static quenching occurred in these systems because of the formation of new complexes among vegetable proteins and potassium sorbate. The apparent binding constants(KA) between PSS and SPI were 1.58×104L/mol(281 K), 1.49×103L/mol(291 K), and 1.11×102L/mol(303 K), respectively. The corresponding binding sites values(n) were 1.25, 0.96 and0.78, respectively. The apparent binding constants between PSS and WG were 2.90×104L/mol, 2.53×104L/mol and 5.50×104L/mol at 281 K,291 K and 303 K, respectively. And the, corresponding binding sites values(n) were 1.04, 1.06 and 1.15, respectively. The changes of entropy and enthalpy indicated that the interaction of PSS and SPI was driven mainly by Vander waals force and hydrogen bonding, while the interaction of PSS and WG was chiefly driven by hydrophobic interaction and electronic force.