Effects of pea protein on properties of cassava starch edible films produced by blown-film extrusion for oil packaging

Starch can be commercially prepared into edible and biodegradable packaging via plasticization and extrusion. However, plasticized starch has poor stability in blown-film extrusion processability and storage properties which can be improved by combinations with protein. Edible films were developed from acetylated cassava starch (AS) and pea protein isolate (PI) using conventional blown-film extrusion. Films with PI up to 20 % were determined for physical, thermal and barrier properties and stability for oil packaging. PI stabilized films during blown-extrusion but decreased flexibility due to strong inter- and intra-molecular interaction with non-homogeneity of AS-PI blend matrices. Protein dispersed in AS matrices at low PI and formed continuous networks at 20 % which led to increased tensile strength. Increase in PI decreased solubility and light transmission but increased protein aggregation and improved crystallinity, surface hydrophobicity and barrier properties against water vapor and oxygen. Increase in PI also reduced glass transition and relaxation temperatures of AS-PI blends. Heat-sealed AS and AS-PI sachets showed effective protection for soybean and olive oil stored for 3 months at different humidities. PI blending effectively prevented humidity-induced shrinkage of AS film (up to 55 %) and enhanced polymer-glycerol interaction which improved thermal stability. Blending of starch and plant-derived pea protein effectively improved blown-film processability and barrier properties for oil-based food products.