1. China Agricultural University, Key Laboratory of Functional Dairy, Ministry of Education, Beijing 100083, China 2. Beijing Higher Institution Engineering Research Center of Animal Product, Beijing 100083, China 3. COFCO Limited, Beijing 100020, China 4. University of Alberta，Edmonton, Alberta, Canada
Abstract：The interaction between caffeic acid and milk protein (α-casein, β-casein, κ-casein, α-lactalbumin, β-lactoglobulin) were studied in this work. The binding constant KA, binding force, binding distance r0 and transfer efficiency E were evaluated by UV-absorption and fluorescence spectroscopy. The antioxidant capacity of the combination was determined using both 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and ferric reducing antioxidant power (FRAP) assay. The results showed that the interaction between milk protein and caffeic acid resulted in the endogenous fluorescence quenching of milk protein, which belongs to a static quenching mechanism. The negative sign of free energy meant that the interaction process was spontaneous. The strength between caffeic acid and α-casein was electrostatic attraction (ΔH<0, ΔS>0), and that between β-casein and α-Lactalbumin was hydrogen bonding (ΔH<0, ΔS<0). In addition, the strength of caffeic acid interacting with κ-casein and β-lactoglobulin was hydrophobic interaction (ΔH>0, ΔS>0). The binding distance (r0<7 nm) proved that caffeic acid lead to a static quenching mechanism of milk protein. The antioxidant capacity of caffeic acid was inhibited by milk protein to different degrees.
Key words：Caffeic acid;Milk protein;Binding;Fluorescence and UV spectrum;Antioxidant
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