45D-4 |
Molecular dynamics of SPI (soy-protein isolate) films plasticized by water and glycerol |
S. G. CHOI1, W. L. Kerr1, K. M. Kim2, M. A. Hanna2, and C. L. Weller2. (1) Dept. of Food Science & Technology, Univ. of Georgia, Food Science Bldg., Athens, GA 30602-7610, (2) Industrial Agricultural Products Center, Univ. of Nebraska, Lincoln, 233 L.W. Chase Hall, Lincoln, NE 68583-0730 Edible films generally consist of a high molecular weight film-forming polymer and a plasticizer. Plasticizers, such as glycerol, are used in protein-based films to increase film flexibility and processibility, and to induce changes in mechanical and barrier properties. Water may also significantly influence the physical and functional properties as well as the plasticizing ability of an added plasticizer in edible films. Our objectives were to investigate the effects of water and glycerol in different levels on the molecular mobility and plasticizing ability of an SPI-based film, and to study the interaction between the water and glycerol molecules. SPI-films were prepared with glycerol at concentrations of 30%, 50%, and 70%, based on dry SPI weight. Film samples were equilibrated over 0~0.81 aw. Pulsed proton NMR was used to identify and quantify the molecular motion through the analysis of transverse (T2) and longitudinal (T1) proton relaxation. The distributed transverse relaxation of film samples showed two distinct components: a rapidly decaying component (T2s*; ranged 8.8 to 10.0 µs) and a slowly decaying component (T2m*; ranged 140 to 180 µs). T2s* increased with increasing glycerol content, indicating an increase in plasticizing effect. T2s* in films with low glycerol content increased gradually as water content increased, indicating further plasticizing effect of water. However, T2s* in films with high glycerol content showed no change with water content but decrease in integrated signal intensity of rapidly decaying component. All samples had a minimum T1 relaxation values at specific aw. As glycerol content increased, aw values having a minimum T1 decreased. These results suggest that studies on molecular dynamics of films may help to more accurately characterize the roles of glycerol and water in the formulation of protein-based edible films, as well as to better understand the changes in functional properties of the films under different relative humidity conditions.
Session 45D, Food Packaging: General
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