Controlled Loading and Release of Beta-Lactoglobulin in Calcium-Polygalacturonate Hydrogels.

We show here how the structure of polygalacturonate (polyGalA) hydrogels cross-linked by Ca2+ cations via external gelation controls the loading and release rate of beta-lactoglobulin (BLG), a globular protein. Hydrogels prepared from a polyGalA/BLG solution are found to be similar to those obtained from a polyGalA solution in our previous study (Maire du Poset et al. Biomacromolecules 2019, 20 (7), 2864-2872): they exhibit similar transparencies and gradients of mechanical properties and polyGalA concentrations. The nominal BLG/polyGalA ratio of the mixtures is almost recovered within the whole mixed hydrogel despite such strong concentration gradients, except in the part of the hydrogels with the largest mesh size, where more BLG proteins are present. This gradient enables one to tune the amount of protein loaded within the hydrogel. At a local scale, the proteins are distributed evenly within the hydrogel network, as shown by small-angle neutron scattering (SANS). The release of proteins from hydrogels is driven by Fickian diffusion, and the release rate increases with the mesh size of the network, with a characteristic time of a few hours. The specific structure of these polysaccharide-based hydrogels allows for control of both the dosage and the release rate of the loaded protein and makes them good candidates for use as oral controlled-delivery systems.

Altered Thermal and Mechanical Properties of Spruce Galactoglucomannan Films Modified with an Etherification Reaction.

Native hemicellulose lacks many of the properties that make fossil fuel-based polymers excellent for use in today's industrial products and processes. The mechanical and thermal properties of the hemicellulose can, however, be modified, and its processability increased. We functionalized galactoglucomannan to lower its glass transition temperature (Tg) and thereby increase its processability. The functionalization was achieved through an etherification reaction with butyl glycidyl ether used at three molar ratios. Films were produced, and their mechanical and thermal properties were evaluated. Thermogravimetric analysis showed that increased substitution increased the degradation temperature and decreased the water content in the sample, implying increased hydrophobicity upon modification. Dynamic mechanical analysis indicated that butyl glycidyl ether functionalization alters the thermal properties of the modified films both in the absolute values of Tg and in the strength of the films. The etherification reaction resulted in a more ductile material than the unmodified galactoglucomannan (GGM).

Periodate oxidation of xylan-based hemicelluloses and its effect on their thermal properties.

Hemicellulose from pulp mill process water and crop residuals from food production often end up in waste streams or burnt for energy contribution. These waste products contain valuable biopolymers but lack many attributes needed for use in applications such as food and medical or consumer products. This study reports on an investigation of the periodate oxidation of hardwood xylan and arabinoxylan (AX) from wheat bran to produce materials with new functionalities. The study explores how to control the oxidation degree and describes structural differences between the two xylan-based polymers. For the xylan samples, the oxidation resulted in a lowering of the glass transition temperature (Tg), indicating a more flexible chain due to ring-opening of the xylan anhydro-sugar units. For the AX samples, the arabinose side-groups were instead oxidized, hindering oxidation on part of the xylose units, which resulted in a crosslinked network with an unchanged Tg but reduced intrinsic viscosity.

Branching of hemicelluloses through an azetidinium salt ring-opening reaction.

During the last century there has been a steady increase in the number of publications on practical applications of hemicellulose. Due to the water and moisture sensitivity, poor film-forming ability and lack of thermal processability most of the hemicelluloses need to be chemically modified prior to processing into materials. Within this study we present the results of azetidinium salts as a new functional group for conjugation to polysaccharides. The reactivity of three azetidinium salts on xylan, arabinoxylan and galactoglucomannan was investigated. Carbonyl groups were found to be favorable for the reaction with azetidinium salts and thus the glucuronic acid content in the hemicellulose determines the degree of substitution. TEMPO-oxidation of the hemicelluloses was done which successfully increased the degree of substitution. The highly reactive azetidinium salts are easily synthesized from secondary amines and epichlorohydrin and can be used as a new tool toward functionalization of hemicelluloses into the after sought properties.