Soy protein isolate–dialdehyde starch films

Abstract

This study was conducted to determine the effect of dialdehyde starch (DAS) on selected physical properties of cast soy protein isolate (SPI) films. Films were cast from heated (70°C for 20 min) alkaline (pH 10) aqueous solutions of SPI at 5 g/100 ml water, glycerin (50%, w/w, of SPI), and DAS at 0, 5, 10, 15, or 20% (w/w) of SPI. For all types of films, Hunter color values ( L, a, and b), tensile strength (TS), percentage elongation at break (E), water vapor permeability (WVP), moisture content (MC) after conditioning at 50% RH and 25°C for 48 h, and total soluble matter (TSM) after immersion in water at 25°C for 24 h were measured. DAS addition increased ( P<0.05) film yellowness (+ b values) suggesting occurrence of cross-linking between SPI and DAS. Films with 5 or 10% DAS had increased ( P<0.05) TS compared to control films, whereas film E was not significantly ( P>0.05) affected by DAS. Small increases ( P<0.05) in WVP and MC were observed for DAS-containing films, most likely due to water absorption by hydrophilic groups along the DAS polymer chains. TSM of SPI films was significantly ( P<0.05) reduced by DAS by as much as 50% (from 28.6% for control films to 14.4% for films with 20% DAS). DAS showed potential for increasing resistance of SPI films to breakdown in water, thus improving their functionality in envisioned packaging and mulching applications.