Tannic acid: A versatile and effective modifier for gelatin/zein composite films

Zein particles (ZPs) fabricated by an in situ method were applied as fillers to produce gelatin (GA)-based biocomposite films. Tannic acid (TA) was used to modify the microstructure of GA/zein composites and the interactions between ZPs and GA matrix. Field emission-scanning electron microscopy results showed that TA addition could transform the size of ZPs from micron- level to small size (even to nano- level). These changes in the microstructure of composites strongly affected the mechanical properties and surface hydrophobicity of the obtained films. Results indicated that the mechanical properties and surface hydrophobicity of composite films filled with ZPs modified by TA were enhanced greatly compared with those of the neat GA or GA/zein films. The tensile strength and water contact angle value of the GA/ZPs/TA composite were improved from 41.79 MPa to 61.05 MPa and 90.53° to 133.83° with the introducing 10 % zein and 5 % TA into the GA matrix, respectively.