Preparation of pH-sensitive and antioxidant packaging films based on κ-carrageenan and mulberry polyphenolic extract

In this study, antioxidant and pH-sensitive kappa-carrageenan based films were developed by incorporating different amounts of mulberry polyphenolic extract (MPE). Due to abundant anthocyanin content, MPE showed pH sensitive property with solution color changed from red to purple and final gray when pH value increased from 2 to 13. When MPE was incorporated into kappa-carrageenan film, the composite films presented blue color. Notably, the incorporation of 2 and 4 wt% of MPE could significantly increase the thickness, tensile strength, thermal stability, antioxidant activity and pH-sensitive property of kappa-carrageenan film. However, the moisture content, water vapor permeability, UV-vis light transmittance and elongation at break were greatly reduced when 2 and 4 wt% of MPE were incorporated. In addition, kappa-carrageenan-MPE films exhibited heterogeneous and rougher surfaces as compared with kappa-carrageenan film. The existence of intermolecular interactions between MPE and kappa-carrageenan matrix was confirmed by infrared spectroscopy and X-ray diffraction. When applied to monitor the freshness of milk, kappa-carrageenan-MPE films showed evident color changes as milk deteriorated after storage at 40 degrees C for 8 h. Our results suggested that kappa-carrageenan-MPE films could be used as novel active and intelligent food packaging materials. (C) 2019 Elsevier B.V. All rights reserved.