SOY PROTEIN ISOLATE DIALDEHYDE STARCH FILMS

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 degrees C for 20 min) alkalin e (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 t ypes 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 degrees C f or 48 h, and total soluble matter (TSM) after immersion in water at 25 degrees C for 24 h were measured. DAS addition increased (P < 0.05) f ilm yellowness (+ b values) suggesting occurrence of cross-linking bet ween 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 ob served for DAS-containing films, most likely due to water absorption b y hydrophilic groups along the DAS polymer chains. TSM of SPI films wa s 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 poten tial for increasing resistance of SPI films to breakdown in water, thu s improving their functionality in envisioned packaging and mulching a pplications. (C) 1998 Elsevier Science B.V. All rights reserved.