Comparison of the physical and functional properties of food packaging films containing starch and polyphenols from different varieties of wolfberry

Wolfberry is a functional food rich in polyphenols. In this study, polyphenols from different colored wolfberry viz. red wolfberry (Lycium barbarum L.), yellow wolfberry (Lycium barbarum L. var. auranticarpum K. F. Ching) and black wolfberry (Lycium ruthenicum Murr.) were incorporated into starch/polyvinyl alcohol blend to develop food packaging films. The physical and functional characteristics of the films containing different wolfberry extracts were compared. Results showed the total phenolic content of red, yellow and black wolfberry extracts was 53.36, 45.72 and 234.61 mg GAE/g, respectively. Red and yellow wolfberry extracts improved the homogeneity of the film, while black wolfberry extract enhanced the compactness of the film. Hydrogen bonds were the main intermolecular interactions between wolfberry extracts and film matrix. Wolfberry extracts reduced the light transmittance, water vapor permeability and oxygen permeability of the film; however, increased the water contact angle, tensile strength, and antioxidant and antimicrobial activities of the film. The film containing black wolfberry extract showed the lowest light transmittance and oxygen permeability but the highest antioxidant and antimicrobial activities. Moreover, black wolfberry extract made the film show remarkable color changes under different buffer solutions and ammonia atmosphere. Results suggested the films containing wolfberry extracts were promising for food packaging.