Molecular Dynamics of Soy‐Protein Isolate Films Plasticized by Water and Glycerol

Abstract

ABSTRACT: The effects of water and glycerol on the molecular mobility of a soy‐protein isolate (SPI)‐based film were investigated using 1 H nuclear magnetic resonance (NMR). SPI‐films were prepared with different glycerol contents and equilibrated to various levels of water activity (a w ). The distributed transverse relaxation of film samples showed 2 distinct components: a solid‐like fraction (T 2s *) and a liquid‐like fraction (T 2m *). The peak T 2s * values of films with lower glycerol concentration were more sensitive to variation in a w . As a w increased, the change of solid‐like to liquid‐like fraction was observed in higher glycerol films. As glycerol content increased, a minimum longitudinal relaxation time (T 1 ) occurred at lower a w . Our results suggest that NMR techniques can be used to quantify the plasticizing effects on biopolymer films.