Development, characteristics and biological activities of bilayer composite film based on gelatin/-carrageenan loading curcumin and -polylysine

Using curcumin and epsilon-polylysine (epsilon-PL) as functional ingredients, one bilayer composite film was prepared by flow casting method using gelatin and kappa-carrageenan as the outer- and inner-film layers, respectively. Compared with the inner kappa-carrageenan film loading 3 wt% curcumin and 0.1% epsilon-PL (01CF) or 3 wt% curcumin and 0.3% epsilon-PL (03CF), the transparency, tensile, and water contact angle of the bilayer composite film were significantly increased. X-ray diffraction results revealed that the inner film matrix of kappa-carrageenan interacted well with curcumin and epsilon-PL. Scanning electron microscopy observed that the cross-sectional surface of the inner and outer layers in the bilayer composite film was smooth and had good compatibility. In atomic force microscopy image, the inner surface of the bilayer composite film had lower root mean square roughness and average roughness than the outer film surface. The crystallinity of curcumin in the bilayer composite film loading 0.3% epsilon-PL was dramatically reduced in confocal laser scanning microscope images compared to that of the composite film with 0.1% epsilon-PL addition. The bilayer composite film demonstrated good scavenging activity on DPPH radical with inhibition rate >65%, and showed strong inhibition effect on the spoilage bacteria derived from Penaeus vannamei. Furthermore, the bilayer composite film showed sensitive response to volatile amines by visible color changes from yellowish to reddish brown. In conclusion, the prepared bilayer composite film could have potential application prospects in the field of natural active food packaging materials for shrimp products.