Use of gamma-irradiation cross-linking to improve the water vapor permeability and the chemical stability of milk protein films

gamma-irradiation was used to produce free-standing cross-linked milk proteins. Film forming solutions were prepared according to a method previously developed in our laboratory using calcium caseinate (cas) with various proportions of whey protein isolate (wpi) or whey protein concentrate (wpc). The following caseinate-whey protein (cas:wp) ratio were prepared: 100:0, 75:25, 50:50, 25:75, and 0:100. The WVP of the films was determined gravimetrically at 23degreesC using a modified ASTM procedure. Molecular properties characterization was performed by size exclusion chromatography (SEC). Results showed significant (p,less than or equal to0.05) reduction of the WVP of protein films for the following formulations: cas:wpi or cas:wpc (100:0); cas:wpi (25:75); cas:wpc (25:75); and cas:wpc (0:100). Mixture of cas and wpi produced a synergistic effect. The strongest combined effect was obtained for cas:wpi (25:75) formulation with permeability values of 2.07 and 1.38 g mm/m(2) dnm Hg for unirradiated and irradiated samples, respectively. gamma-irradiation also induced a substantial increase of high molecular weight protein components in film forming solutions. The predominant fraction was greater than or equal to 10 x 10(6) Da for irradiated film forming solutions, compared to less than 0.2 x 10(6) Da for native unirradiated solutions. (C) 2002 Elsevier Science Ltd. All rights reserved.