A comparison on the binding mechanisms of zein and gliadin with curcumin to guide the self-assembly of nanoparticles for delivery purpose

Using prolamins to prepare delivery systems is promising for pharmaceutical and food industries. It is very necessary to find a reliable strategy to probe the assembly-release mechanisms of prolamin-based delivery sys-tems, which could accelerate the screening of fabrication conditions. In this study, interactions of zein and gliadin with curcumin at different temperatures and ethanol concentrations was investigated by fluorescence quenching and other spectroscopic methods. It was found that the binding affinity between curcumin and gliadin gradually decreased with increasing ethanol concentration, but that of curcumin-zein gradually increased with increasing ethanol concentration. Zein and gliadin showed highest binding constant values (Ka) of 2.29 x 105 L mol-1 at 80% ethanol and 293K, 2.0 x 105 L mol-1 at 60% ethanol and 293 K, respectively. The temperature -dependent thermodynamic parameters were calculated. And the main driven forces were determined to be electrostatic interactions for gliadin-curcumin complexation, while van der Waals forces and hydrogen bonding were also involved in the binding of zein with curcumin in low ethanol conditions (60-70%). The curcumin-encapsulated zein/gliadin nanoparticles were prepared at various conditions, and their physicochemical prop-erties were compared. The highest EE and LC values of zein nanoparticles were observed at 80% ethanol (95.8% and 19.2 & mu;g/mg), while those of gliadin were observed at 60% ethanol (95.7% and 19.1 & mu;g/mg). The change of encapsulation efficiency and loading capacity of nanoparticles was basically consistent with the binding affinity tendency between curcumin and zein/gliadin, confirming that the fluorescence quenching method is applicable to guide the screening of encapsulants and fabrication conditions.