Mechanisms to enhance functionality of peanut-based biopolymer films

Peanut protein has a strong potential in replacing synthetic packaging based on environmental concern as an agricultural polymer. In this study, methodologies were developed to produce biopolymer films from peanut protein isolate (PPI), and film forming procedures with different treatments were investigated. Distilled water was added to the PPI, which was made from defatted peanut flour, to provide a 5% protein content in the film-forming solution. Ninety percent glycerol was tested as an optimal plasticizer. Film was formed at 90°C for 16 h, and then peeled off after cooling. Attempts were made to enhance the film properties by using physical (heat curing, ultraviolet, ultrasound) and chemical (anhydrides and aldehydes) methods.; Analyses of the films were performed with different techniques involving physical properties (color, thickness, solubility), tensile strength, barrier properties (oxygen and water vapor), rheological properties (stress relaxation), glass transition temperature, and microscope images (ESEM).; Optimal physical treatments were chosen based on the mechanical strength and barrier properties: heat curing for 30 min at 70°C, ultraviolet irradiation for 24 h, and ultrasound process (the probe with water bath method) for 10 min.; The degree of cross-linking was defined from the stress relaxation parameters. Films functionality was strongly affected by the degree of cross-linking. Effective treatment promotes cross-linking in the protein polymer network, and it made films stronger, more compact, and less permeable to water vapor and oxygen.; The glass transition temperature of peanut protein films ranged from 93.6 to 143.2°C. The relationship of the degree of cross-linking and glass transition temperature was described by a linear equation.; Heat curing was the most effective modification for peanut protein films, followed by the ultraviolet irradiation, aldehyde treatments, based on the improvement of increased mechanical strength, reduced water solubility, and reduced barrier properties. Anhydride treatments did not show any significant effect compared with the untreated (control) films in the exception of increased water solubility.