Insight into effect of pigment removal on leaf protein-based bionanocomposite film properties

Capsicum and alfalfa leaves contain numerous leaf proteins (LP) and cellulose resources, making them excellent raw materials for preparing protein-based bionanocomposites films (PBBFs). However, the pigment in LP leads to PBBFs with low light transmission, which limits their application in food packaging. Bleaching can remove pigments; however, its effect on LP and PBBFs remains unknown. This study investigates the effects of pigment removal on the physicochemical and material properties of PBBFs in three dimensions: raw materials, film-forming liquids (FFLs), and PBBFs. The results showed that pigment removal significantly reduced the lignin content of LP, while altering their amino acid composition and thermal properties. The apparent viscosity and stability of FFLs decreased after pigment removal. The PBBF microstructure also changed. The mechanical properties and water sensitivity of PBBFs decreased slightly after pigment removal. This was related to the strength of the hydrogen bonding interactions between the LP and cellulose nanofibers (CNFs), and also to the conformation of the protein and the degree of amino acid exposure within the PBBFs. Pigment removal significantly improved PBBF chromaticity values and light transmission. PBBFs block UV radiation before and after pigment removal and can be used for photochemically sensitive food packaging.