|Ph.D Student||Semyonov David|
|Subject||Developing Nano-Sized Vehicles Based on Tailored|
Oligosaccharides and Polysaccharides Produced by
Organic and Enzymatic Synthesis
|Department||Department of Biotechnology and Food Engineering||Supervisors||Professor Shoham Yuval|
|Dr. Shimoni Eyal|
|Full Thesis text|
The overall goal of this research was to develop nano-size vehicles, for hydrophobic nutraceuticals of low solubility and poor bioavailability, based on new dendritic and polysaccharide architectures produced enzymatically. Our hypothesis was that potentially useful dextran based nano-sized structures can be obtained by the enzymatic synthesis of dextransucrase. To achieve this objective we explored two dextransucrase synthesis procedures for obtaining nano-size vehicles suitable for hydrophobic nutraceuticals. The first generation of enzymatically synthesized dextran nanoparticles contained genistein or stearic acid (SA). The first procedure was to generate dextran nano particles by applying dextransucrase polymerization reaction. Under optimal conditions (pH 5.2-6 and sucrose concentration > 0.5 M), dextransucrase generated spherical dextran nanoparticles (100-450 nm). Two inclusion methods were employed utilizing either DMSO or acidification. Optimization of the inclusion processes lead to nano sized dextran particles containing genistein and SA. The particles were characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray Diffraction (XRD) and cryogenic-transmission electron microscopy (cryo-TEM). The DMSO method was found to be more suitable for the inclusion of genistein in dextran resulting in higher content (5.7±0.1 g genistein /100 g), and higher % of nano-size particles (87%, 105-400 nm). The acidification method gave better results for inclusion of SA in dextran nano particles resulting in higher content (11.0±1.5 g SA /100 g) and higher area/volume ratio (38±15 m2/ml). For both protocols the freeze drying step exerts a dominant effect presumably due to the formation of new hydrogen bonds and Van der Waals interactions.
The second synthesis procedure involved the use β-cyclodextrins (CD) as an acceptor in the dextransucrase reaction. It was found that β-CD molecule can “accept” the glucosyl group to give a 6-o-α-glucosyl-β-CD product, and can “accept” the dextranyl group resulting in a dextranyl-β-CD product. Dextranase digestion of the acceptor reaction products produced water soluble substituted β-CD [(6-o-α-glucosyl)n-β-CD]. Enzymatically substituted β-CD was used to improve solubility of genistein and naringenin. Genistein and naringenin solubility at 37°C were increased upon complexation with (6-o-α-glucosyl)n-β-CD by 320-fold and by 120-fold, respectively. Phase solubility study pointed out the formation of 1:2 stoichiometric complexes between the flavanoids and the enzymatically substituted β-CD that were also influenced by temperature variations.