Storage-induced changes in functional properties of glycerol plasticized - Soybean protein concentrate films produced by casting

Aging of soybean protein concentrate (SPC) films plasticized by glycerol obtained by casting and stored at 25 +/- 2 degrees C and 65 +/- 2% relative humidity was systematically investigated over a period of 90 days. Aging promoted the reorganization of the secondary structure of protein fraction in SPC into others with prevalence of extended beta-sheet conformation. Stabilizing interactions also progressed to increasing contribution of disulfide cross-links and Maillard aggregates through the carbohydrate fraction of SPC. Such time-dependent structural changes were ineffective in retaining glycerol within the films. This caused increased strength and stiffness with time. Water vapor permeability values increased up to 90th day due to micro-cracks created by film contractions during storage, which create more permeable structures which hamper the determination of oxygen permeability on aged films. As a general trend, films functional properties remained stable for two weeks under specific storage conditions preserving enough mechanical and barrier properties to act as efficient protective food packaging materials. (C) 2014 Elsevier Ltd. All rights reserved.