Physical properties of egg white-dialdehyde starch films

Films were cast from heated (40 degrees C for 20 min) alkaline (pH 11.25) aqueous solutions of egg white (EW) solids (9 g/100 mL of water), polyethylene glycol 400 (60% w/w of EW), yolk solids (10% w/w of EW), and dialdehyde starch (DAS) at 0, 2.5, 5, 7.5, or 10% (w/w) of EW. For all types of films, tensile strength (TS), percentage elongation at break (E), Hunter color values (L, a, and b), total soluble matter (TSM) after immersion in water at 25 degrees C for 24 h, and protein solubility (PS) after immersion for 12 h in buffers (pH 8) containing urea and urea/2-mercaptoethanol were determined. DAS addition increased (P < 0.05) film TS and yellowness (+b values) and reduced (P < 0.05) film TSM and PS in both buffer systems. These modifications in film properties suggested occurrence of cross-linking between EW protein and DAS. This was further supported by SDS-PAGE patterns. Such patterns for DAS-containing films revealed bands of aggregates, increasing in intensity with increasing amounts of DAS, which were absent from patterns of control EW films.