Molecular Packing in Amorphous Carbohydrate Matrixes

Abstract

The molecular packing of bidisperse matrixes of amorphous carbohydrates consisting of a fractionated maltopolymer supplemented with various amounts of the disaccharide maltose is investigated by combining Positron Annihilation Lifetime Spectroscopy (PALS) with specific volume measurements. The maltopolymer-maltose blends are equilibrated at a range of water activities between 0 and 0.75 at 25 degrees C in order to investigate the effect of water content and carbohydrate molecular weight distribution on the size of the molecular free volume holes in both the glassy and rubbery states. In the rubbery state, the size of the intermolecular holes is only very weakly dependent on the carbohydrate molecular weight, provided that the carbohydrate blends are analyzed at the same water content. In contrast, in the glassy state, significant differences in the size of the free volume holes are observed between the various blends at constant water content. Both the specific volume and the hole volume decrease with increasing maltose content, initially rapidly up to a maltose content of about 40 wt % on total carbohydrate. In addition, we find that the role of water as a plasticizer and matrix constituent is a complex one. At very low water contents, water acts by filling the free volume holes between the carbohydrate molecules. This hole-filling mechanism could well be related to the phenomenon of anti-plasticization observed before. At higher water contents, corresponding generally to water activities above 0.11 at 25 degrees C, water conversely increases the average hole volume in the carbohydrate matrixes, most likely caused by water interfering with the hydrogen bonding between the carbohydrate molecules, leading to a local expansion of the molecular packing.

Differences in Free Volume Elements of the Carrier Matrix Affect the Stability of Microencapsulated Lipophilic Food Ingredients

“…As discussed above, the average hole size increases linearly with τ o-Ps . The values presented in the present study are similar to values obtained in the literature 29 . Although the difference within the measured series of samples was small, it is still significant with respect to lipid oxidation especially when taking into consideration that the diffusivity is exponentially related to the radius of the free volume elements.…”

Proteins in Saccharides Matrices and the Trehalose Peculiarity: Biochemical and Biophysical Properties

“…dextrans) may also have biopreserving effects because of their high Tg, despite their lower ability to interact directly with protein or membrane surfaces [26]. They are indeed largely excluded from the biomolecule surface, because of their large free volumes and steric hindrance [56,57]. In this respect, it is to be observed that the basic working mechanism of polymeric sugars is more or less the same as that of all the high molecular components in vivo, i.e.…”

“…In this case, the solvent appears like a porous medium where smaller biomolecules can diffuse, despite the high viscosity of the solution [63]. In this scenario, mono-or disaccharides could synergistically contribute to bioprotection, because they can settle in the oligosaccharide matrix, enhancing the matrix capability to interact with embedded structures [57,64]. Actually, disaccharides combined with long chain maltopolymers (e.g., maltodextrin or starch) are widespread as glass formers in food industry.…”

Free Volume, Molecular Mobility and Polymer Structure: Towards the Rational Design of Multi-Functional Materials

“…[1012, 21,22]. In addition, plasticisation is commonly accompanied by a signicant increase in the diusional mobility of small molecules (e.g.…”