Properties of Peanut Protein Film: Sorption Isotherm and Plasticizer Effect

The objectives of this study were to determine the effect of type and level of plasticizer on film properties and determine their sorption isotherms. Peanut protein films were formed by using four types of plasticizer (glycerin, sorbitol, polyethylene glycol and propylene glycol) at three levels (0.67, 1.17, 1.67 g/g of protein content). Sorption isotherms of peanut protein at pH 6.0, 7.5 and 9.0 were determined. Glycerin showed the best performance as a plasticizer compared to the others. The concentration of glycerin between 0.67 and 1.67 g/g of protein did not affect the water permeability and oxygen permeability. However, tensile strength decreased (from 5.14 to 4.10 MPa), with an increase of glycerin from 1.17 to 1.67 g/g of protein and percent elongation increased (from 105 to 164%) when glycerin increased from 0.67 to 1.67 g/g of protein. Peanut protein was very hydrophilic, the equilibrium moisture content of film increased sharply at pH 7.5 and 9.0 (0.602 and 0.939 and 0.621 to 1.083 g/g of dry matter, respectively) with an increase in relative humidity (RH) from 75 to 93% RH. Film thickness depended on the RH, and film at pH 6.0 showed the greatest change in film thickness with increasing RH.