Study Of Cysteine Proteases Hydrolysis Of β-casein/theaflavin Complex Films

Objective: To investigate the hydrolytic rates of three kinds of cysteine proteases(papain, bromelain and ficin) to the complex films (dephosphorylated bovine milkβ-casein (β-CN (DP))/theaflavin (TF)) and the ability of TF adsorption for the secondtimes on the remnants films after being treated by enzymes. Methods: The β-CN (DP)film was built on the sensors of quartz crystal microbalance with dissipation (QCM-D)by self-assembled monolayers on where TF was adsorbed to form the β-CN(DP)/TFcomplex films. Inspecting changing curve of frequency and time for hydrolysis theβ-CN (DP)/TF complex films after papain, bromelain and ficin were injected into themeasurement cell. Data of frequency and time shifts were fitted by Boltzmannequation from which the hydrolysis rates (1/C) could be calculated in order tocompare the differences of the hydrolytic rates among different enzymes. Theroot-mean-square roughness, topography and hydrophilic-hydrophobic property of thecomplex films before and after hydrolysis were characterized by atomic forcemicroscope and contact angle measurement, respectively. The TF adsorption onresidual films for the second times after being treated with various enzymes wascarried out, and the relative parameters (Δm and Δh) were caculated and comparedwith those of TF adsorption on the β-CN (DP) film for the first time. Result: Thebehavior of TF adsorption onto the β-CN (DP) surface can be better interpreted by theFruendlich isotherm. The hydrolytic rates for three kinds of cysteine proteasesfollowed as ficin> papain> bromelain (P <0.05). The root-mean-square roughnesseson the residual film after hydrolysis were ficin> papain and bromelain (P<0.05), andThe roughness between papain and bromelain was no significant difference instatistics (P>0.05). The mass and thickness of TF adsorption on residual films weresmaller than those of TF adsorption for the first time (P<0.05), but there were nostatistically significant differences among three kinds of cysteine proteases (P>0.05).Conclusion: The β-CN (DP)/TF complex films can be hydrolyzed effectively by threekinds of cysteine proteases (papain, bromelain and ficin), and the hydrolytic rate officin was the highest among them. TF adsorption on residual films can be prevented insome extent utilizing hydrolytic action above cysteine proteases.