The Effect of Molecular Size on Molecular Mobility in Amorphous Oligosaccharides

Abstract

The physical properties and especially the molecular mobility of amorphous carbohydrate matrixes directly influence the stability of foods, feeds, and pharmaceuticals and the dessication tolerance of animals and plants during anhydrobiosis. Phosphorescence of the sodium salt of erythrosin B was used to investigate the local molecular mobility in pure amorphous solids of a homologous series of malto-oligosaccharides (maltose, G 2 ; maltotriose, G 3 ; maltotetraose, G 4 ; maltopentaose, G 5 ; maltohexaose, G 6 ; and maltoheptaose, G 7 ); sucrose and maltodextrin DE18 (a hydrolytic fraction of starch) were investigated for comparison. Measurements of the temperature-dependence of the phosphorescence emission energy, an indicator of the extent of local dipolar relaxation, and the phosphorescence emission lifetime, an indicator of the rate of collisional quenching of the excited state by matrix molecules, demonstrate that the local matrix molecular mobility increases with molecular size, and thus, with an increase in T g , in these glucose oligosaccharides. Master curves of the spectroscopic measures of matrix mobility for each oligosaccharide, plotted against T-T g , were not superimposable, suggesting that local properties of the amorphous sugar matrixes, rather than T g per se, influence local matrix mobility. Indicators of spectral heterogeneity also varied with molecular size, indicating that dynamic site heterogeneity also increased with molecular size and thus, T g . These results emphasize the importance of additional research in developing appropriate "molecular rules" for designing amorphous matrix systems with better long-term stability for foods, feeds, or pharmaceuticals.

Surface photo-crosslinking of plasticized thermoplastic starch films

“…The bands at 1339 cm À1 were assigned to CAH bending [24]. The absorption peaks at 1149 cm À1 and 1076 cm À1 were attributed to stretching vibrations of CAO in CAOH groups [25,26].…”

Influence of glycerol on the molecular mobility, oxygen permeability and microstructure of amorphous zein films

“…Values of k o TS1 for Ery B reported in the literature vary from 0.3 Â 10 7 s À1 in ethanol and 6.5 Â 10 7 s À1 in water (Duchowicz et al, 1998) to 111 Â 10 7 s À1 in solid polyvinyl alcohol (Lettinga, Zuihof, & van Zandvoort, 2000). We estimated the maximum possible value for k o TS1 in zein with 20% glycerol by assuming that k TS1 (T) cannot result in values for k TS0 that decrease with temperature (You & Ludescher, 2010). This procedure thus estimated the minimum possible values of k TS0 (T).…”

“…The decay rate is expressed by k TS0 , which reflects the rate of quenching of the probe due to coupling of the excited T 1 state to a highly excited vibration of the ground S 0 state followed by dissipation of vibrational energy from the probe into the matrix. This value of k TS0 is thus a measure of overall matrix molecular mobility in the local region around each probe (You & Ludescher, 2010). The temperatureedependence of k TSO can be calculated from measurements of the Ery B lifetime under nitrogen using Eq.…”

Effects of Mono‐, Di‐, and Tri‐Saccharides on the Stability and Crystallization of Amorphous Sucrose

“…The delayed sucrose crystallization was attributed to the higher T cry and increased viscosity above the T g in the presence of fructose (Roos & Karel, ). In addition, the molecular mobility in thin films containing sucrose with glucose, maltose, and maltotriose was studied using phosphorescence of the sodium salt of erythrosin B (You & Ludescher, ). As the molecular size of the additive increased, the dynamic size heterogeneity in glasses was found to increase, which in turn was thought to indicate a broader distribution of molecular mobility (You & Ludescher, ).…”

“…In addition, the molecular mobility in thin films containing sucrose with glucose, maltose, and maltotriose was studied using phosphorescence of the sodium salt of erythrosin B (You & Ludescher, ). As the molecular size of the additive increased, the dynamic size heterogeneity in glasses was found to increase, which in turn was thought to indicate a broader distribution of molecular mobility (You & Ludescher, ). Fewer studies have succeeded in correlating the crystallization behavior studied at higher temperatures to amorphous sucrose stability in controlled RH and lower temperature environments that are more representative of common food storage conditions (Saleki‐Gerhardt & Zografi, ).…”