Abstract
Abstract This work aimed to study the effect of starch (acetylated di-starch phosphate and starch acetate) and maltodextrin (DE 10.2 and DE 15.6) on the properties of soy protein isolate (SPI) films. Films were cast from heated (70 °C for 20 min) alkaline (pH 10) aqueous solutions of soy protein isolate (8%) containing glycerol (50% of SPI) as a plasticizer and starch or maltodextrin (20% of SPI). For all types of films, water vapor sorption kinetics during 24 h at 25 °C and 75% relative humidity (RH), diffusion coefficient of water vapor, water vapor permeability at 25 °C for two relative humidity differentials (40–75 and 40–100%), tensile strength and elongation at break, color and microstructure were determined after conditioning film specimens at 25 °C and 53% RH for 7 days. Addition of starch and maltodextrin had a significant effect on water vapor adsorption of soy films and increase of diffusion coefficient from 1.73 to 2.60 m2 s− 1. Water vapor permeability increased as relative humidity differentials increased and observed results can be correlated with the plasticizing effect of water. All films demonstrated low values of tensile strength (~ 1.14–1.96 MPa) and elongation at break (~ 25.6–34.7%). All films obtained were opaque and homogenous. Industrial relevance Edible films based on proteins are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. There is a real need to find methods for production of soy films with properties accepted by the industry. One of the solutions is preparation of composite films based on protein and polysaccharide components. This work deals with the physico-chemical behavior of two types of carbohydrate polymers (modified starch and maltodextrins) on the physical–chemical properties of edible films based on soy protein isolate. Moisture sorption and kinetics, mechanical and barrier properties have been studied and related to structure. This paper suggests that physico-chemical properties of soy protein isolate films can be modified by the incorporation of modified starch and maltodextrins.
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