Dehydration of protein lactoferrin-glycomacropeptide nanohydrogels

Abstract

Protein based nanohydrogels have recently gained interest due their high ability to carry and deliver active compounds. However, one of the limitations of using protein-based systems is their high sensitivity to physicochemical stresses during processing and storage. Protein-based formulations are commonly prepared as solid dosage forms once their stability can be achieved in the solid rather than in the liquid state. One of the methods to improve the stability of protein-based systems is drying, being freeze and spray drying the most popular methods. Nanohydrogels composed of lactoferrin and glycomacropeptide were developed by thermal gelation and dried using a freeze-dryer (CHRIST - Alpha 14 LD plus, Germany) and a nano spray dryer B-90 (BÜCHI Labortechnik AG, Switzerland). For nano spray-drying different experimental conditions were tested such as: the inlet temperature (80, 100 and 120°C) and the hole size of the vibrating membrane in the spray cap (4m and 7m), while for freeze drying the nanohydrogels where maintained at 40°C for a drying period of about 24h. The physicochemical properties of the resulting dried nanohydrogels were compared through different techniques: differential scanning calorimetry (DSC), thermogravimetry (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). DSC shows an endothermic peak ranging from 82 to 90°C, indicating that during the drying methodologies the second denaturation peak of lactoferrin (around 90°C) is maintained. No significant differences (p<0.05) for denaturation peak temperatures were observed when different inlet temperatures or spray cap size were applied during the nano spray-drying conditions. When compared with freeze-drying it is possible to observe that a denaturation peak around the same range of temperatures was detected, also indicating that this drying process did not affect the denaturation of the protein. XRD results of nanohydrogels dried by freeze-drying revealed that crystallinity is significantly higher when compared with spray-dried nanohydrogels, explaining the lower thermal degradation observed in TGA for freeze-dried nanohydrogels. Nanohydrogels morphology after the drying process was evaluated by SEM. Nanohydrogels obtained by nano spray dryer B-90 allowed identifying the presence of particles with spherical shape, while nanohydrogels obtained by freeze drying had a sponge-like appearance. This work shows the influence of the drying process of protein-based nanohydrogels in their physical-chemical properties, thus pointing at which will be the preferred technology to be used in a future industrial application.