Development and characterization of nano- microfibers for the encapsulation and release of bioactive phenolic compounds

Research output: Book/ReportPh.D. thesis – Annual report year: 2018Research

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In this PhD project, electrospun nano-microfibers of polysaccharides xanthan gum, and chitosan, as well as phospholipids were investigated as encapsulating matrices of phenolic bioactives, that are the most abundant bioactives in our diet.

The processing of electrospun xanthan gum nanofibers using formic acid as a solvent was reported for the first time (Paper I). Morphological studies by scanning electron microscopy show that uniform fibers with average diameters ranging from 128 ± 36.7 to 240 ± 80.7 nm are formed depending on the polysaccharide concentration (0.5 to 2.5 wt/vol%) (Paper I). At the polysaccharide concentrations where nanofiber formation was observed, an increase of the elastic modulus and first normal stress differences is observed. Fourier transform infrared spectroscopy and circular dichroism measurements indicated that an esterification reaction took place, where formic acid reacted with the pyruvic acid groups of xanthan. Therefore, formate groups neutralized the pyruvic charges, which in turn stabilized the helical conformation of xanthan.

The potential to utilize electrospun xanthan nanofibers as a delivery carrier system of bioactive phenolic compounds was investigated (Paper II). Gallic acid (GA) and ( ̶ )-epigallocatehin gallate (EGCG) were encapsulated within xanthan nanofibers, and their release was studied in relevant media at pH 6.5 and 7.4. A sustained release of the bioactives up to 60-80% was observed over 8h. Furthermore, the xanthan-GA and xanthan-EGCG nanofibers were incubated with Caco-2 cells, and the cell viability, transepithelial transport and permeability properties across cell monolayers were investigated. An increase of permeability of Ga and EGCG was observed when the polyphenols were loaded into xanthan nanofibers, comparatively to the non-

encapsulated bioactives. These results suggested that xanthan nanofibers have the ability to enhance the transepithelial permeation of phenolic compounds in vitro by inhibiting efflux transporters and opening the tight junctions.

Novel electrospun xanthan-chitosan (X-Ch) nanofibers were developed as a carrier for the delivery of curcumin (Cu), a model hydrophobic phenolic bioactive (Paper III and IV). Nanofibers stable in aqueous media were produced by the electrospinning of X-Ch viscoelastic gels with average diameter of 750 nm. The addition of curcumin led to the increase in average fiber diameters to 910 nm. A sustained release of curcumin of 8-10% from X-Ch nanofibers was observed over a period of 12 h for the different pH media (2.2, 6.5, and 7.4) at 37oC. However, after 120 h, 20% of Cu was released from X-Ch nanofibers in pH 2, while nearly 50% of Cu was released in neutral media, through a non-Fickian mechanism. The data support that X-Ch nanofibers could be used as a carrier for the encapsulation of hydrophobic bioactive compounds with long-term pH-stimulated release properties.

Furthermore, the potential to utilize X-Ch nanofibers to enhance the transepithelial transport and permeability of curcumin across Caco-2 cell monolayer was investigated (Paper IV). After 24 h of incubation, the exposure of Caco-2 cell monolayers to X-Ch-Cu nanofibers resulted in a cell viability of ~80%. A 3-fold increase of curcumin permeability was observed when the polyphenol was loaded into X-Ch nanofibers, compared to the free curcumin. This increased transepithelial permeation of curcumin was induced by interactions between the nanofibers and the Caco-2 cells that led to the opening of the tight junctions.

In the last study of the thesis (Paper V), electrospun phospholipid (asolectin) microfibers were investigated as an antioxidant and encapsulation matrix for curcumin and vanillin. Release

studies in aqueous media revealed that the phenolic bioactives were released mainly due to swelling of the phospholipid fiber matrix over time. Asolectin fibers were observed to have antioxidant properties, which were improved after the encapsulation of the phenolic compounds, as observed from total antioxidant capacity (TAC) and the total phenolic content (TPC) assays. Furthermore, the antioxidant capacity of curcumin/phospholipid and vanillin/phospholipid microfibers was observed to remain stable over time at different temperatures (refrigerated, ambient) and pressures (vacuum, ambient), while the non-encapsulated phenolic compounds decreased their TAC and TPC values. Therefore, this study confirms the efficacy of electrospun phospholipid microfibers as encapsulation and antioxidant systems.
Original languageEnglish
Place of PublicationKgs. Lyngby, Denmark
PublisherTechnical University of Denmark
Number of pages164
Publication statusPublished - 2018

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