María Florencia Mazzobre

Combined effects of trehalose and cations on the thermal resistance of β-galactosidase in freeze-dried systems

The purpose of this study was to investigate the combined effects of trehalose and cations on the preservation of beta-galactosidase in freeze-dried systems and their relationship to physical properties. Differential scanning calorimetry was employed to measure the glass transition temperature (T(g)) and the endothermal peak area, related to the amount of crystalline trehalose dihydrate present in the samples. In systems in which the trehalose matrix was humidified to conditions which allowed a high proportion of trehalose to crystallize, the enzyme was rapidly inactivated upon heating at 70 degrees C. In these conditions the addition of CsCl, NaCl and particularly KCl or MgCl(2), improved the enzyme stability with respect to that observed in matrices containing only trehalose. For a given moisture content, addition of salts produced very little change on the glass transition temperature; therefore the protective effect could not be attributed to a higher T(g) value. The crystallization of trehalose dihydrate in the humidified samples was delayed in the trehalose/salt systems (principally in the presence of Mg(2+)) and a parallel improvement of enzyme stability was observed.

Microscopy and calorimetry as complementary techniques to analyze sugar crystallization from amorphous systems

A comparison of microscopic and macroscopic techniques to evaluate sugar crystallization kinetics is presented using amorphous lactose and lactose-trehalose mixtures. Polarized light video microscopy (PLV) and differential scanning calorimetry (DSC) were applied to measure crystallization kinetics, induction times and time for complete sugar crystallization at different storage temperatures (60-95 degrees C). DSC was also employed to measure the glass transition temperature (T(ag)) of the systems. PLV permitted direct observation, in real time, of growth of individual crystals and morphological aspects at a scale not detected by DSC. Taking the average of several microscopic observations, the results for temperature dependence of crystallization rate and time to complete lactose crystallization were similar to those obtained by DSC. Both PLV and DSC techniques showed that the presence of trehalose delayed lactose crystallization, without affecting the T(ag) value. For the analysis of sugar crystallization in amorphous systems, PLV and DSC proved to be complementary techniques. Validation of results obtained by PLV with results from DSC opens a new area of microstructural analysis of crystallizing systems.

Glass Transition and Thermal Stability of Lactase in Low-Moisture Amorphous Polymeric Matrices

The thermal stability of a commercial preparation of neutral lactase (β‐galactosidase) in low‐moisture amorphous polymeric matrices of maltodextrin (MD dextrose equivalent (D.E.) = 10.9) and polyvinylpyrrolidone (PVP; MW 40 000) stored at various temperatures (T) was studied. The main objective was to analyze the usefulness of the glass transition temperature (Tg) as a parameter for predicting the thermal stability of lactase in low‐moisture glass‐forming matrices. Loss of enzyme activity was observed during storage in glassy conditions (either in PVP or MD matrices), suggesting that, although molecular mobility may be significantly decreased in the glassy state, the protein molecule is still mobile enough to lead to enzyme inactivation. The results indicated that the change from the glassy to the rubbery state of the PVP matrix, where the enzyme was embedded, was not reflected in drastic changes in the temperature dependence of the thermal inactivation rate, as expected if it could be only predicted on the basis of physical changes of the matrices. The plasticizing effect of water is not the only factor to take into account when considering enzymatic stability in heated low‐moisture amorphous systems.

Prosopis alba exudate gum as excipient for improving fish oil stability in alginate-chitosan beads

The aim of the present work was to employ an exudate gum obtained from a South American wild tree (Prosopis alba), as wall material component to enhance the oxidative stability of fish oil encapsulated in alginate-chitosan beads. For this purpose, beads were vacuum-dried and stored under controlled conditions. Oxidation products, fatty acid profiles and lipid health indices were measured during storage. Alginate-chitosan interactions and the effect of gum were manifested in the FT-IR spectra. The inclusion of the gum in the gelation media allowed decreasing the oxidative damage during storage in comparison to the free oil and alginate-chitosan beads. The gum also improved wall material properties, providing higher oil retention during the drying step and subsequent storage. Fatty acids quality and lipid health indices were widely preserved in beads containing the gum. Present results showed a positive influence of the gum on oil encapsulation and stability, being the main mechanism attributed to a physical barrier effect.

Chitin hybrid materials reinforced with graphene oxide nanosheets: chemical and mechanical characterisation

Chitin hybrid materials reinforced with graphene oxide nanosheets (nGO) have been prepared. The chitin : nGO ratio ranged from proportions where chitin was the main component to ones where nGO exceeded chitin. SEM and TEM images showed that high proportions of nGO may result in nanosheet association. FTIR, 13C solid-state NMR and DSC analyses showed that the interaction among the components would not involve the formation of new molecular bonds. nGO was shown to act as a filler that induces structural rearrangements in chitin which lead to new hydrogen bonds among the chains. The mechanical stability proved to be higher when the nGO content in the hybrid was similar to or higher than that of chitin. The rheological behaviour of the material was shown to become more solid-like with increasing nGO content. The nGO did not interfere with lysozyme activity on chitin chains, indicating that these materials would be biodegradable.