Mechanical properties and water vapor permeability of edible films made from fractionated soy proteins with ultrafiltration

Soy protein isolates (SPI) were fractionated by ultrafiltration unit equipped with 100 and 300 kDa cutoff size membranes. Glycerol-plasticized fractionated soy protein films were developed by casting methods. Mechanical, moisture barrier and physical properties of films, as affected by molecular weight of soy protein fraction, were investigated. Tensile strength and percent elongation at break of films increased with molecular weight of soy proteins. However, molecular weight variation did not influence the water vapor barrier properties of films. Protein solubilities of fractionated films were in the range of 3.5-4.6 g/100 g of dry film, whereas 11.9 g of proteins were solubilized from 100 g of dry SPI film. Hunter b value of fractionated protein films decreased with molecular weight of soy protein. (C) 2004 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.