A Study on the Mechanical Properties of Pea Protein Isolate Films

Abstract

Effects of glycerol (Gly) (3–7% w/w) and sorbitol (Sor) (4–8% w/w) concentration, pH (7.0, 9.0, 11.0) and heating (90C, 20 min) of film-forming solutions (FFS) on the tensile strength (σmax), elongation at break (εb), elastic modulus (EM) and puncture strength (PS) of pea protein isolate (PPI) films were investigated in this study. The films plasticized with Sor exhibited significantly higher σmax, EM, PS and lower εb, in comparison with Gly-plasticized films. Incorporation of higher Gly and Sor amounts in the films led to decreases in σmax, EM and PS but did not affect εb. An increase of pH value from 7.0 to 11.0 resulted in improved σmax of Gly-plasticized films, while for films with Sor, this effect was not observed. In turn, εb and PS of the films were significantly increased by alkalization of FFS, regardless of the plasticizer type. Generally, an improvement in mechanical strength of PPI films produced from heated FFS was observed. X-ray diffraction analyses of Gly- and Sor-plasticized PPI films did not show any differences in their internal structure. Practical Applications Edible films may be used as selective barriers to gasses, carriers of antimicrobial agents or agents improving appearance and handling of many different food groups. Most studies suggest their application as edible coatings that may prolong the shelf life of unprocessed plant and animal products. Other possible uses include wraps and separation layers; pouches, bags, food casings, and labels; drug coatings, capsules and microcapsules; paper coatings. The Sor-plasticized PPI films can be promising materials for the applications, e.g., in the fields of fruit and vegetables quality preservation. Because of Sor recrystallization, these films are not suitable for low-water activity food, especially if stored for a long duration at ambient conditions.