Structural and physicochemical properties of hydrophobically-modified phytoglycogen nanoparticles and its potential applications

Phytoglycogen (PG), a water-soluble glycogen-like α-D-glucan nanoparticles presented in the endosperms of the sugary-1 mutant corn, is considered as a promising solubility enhancer and delivery vehicle for lipophilic nutrients recently. However, the practical applications of PG as an oral delivery system in food and pharmaceutical field are limited by their poor stability against enzymatic digestion in small intestine relatively low encapsulation efficiency compared with other delivery systems. Therefore, the major objective of present study was to develop a serial of PG nanoparticles with different hydrophobicity and to investigate the physicochemical properties of obtained amphiphilic nanoparticles and evaluate the feasibility of modified PG as a carrier for hydrophobic bioactive compounds. PG nanoparticles were reacted with acetic-anhydride, valeric-anhydride, or N-caprylic-anhydride in order to obtain the PG nanoparticles with different hydrophobicity. The percentage of acylation was significantly affected by reaction conditions, with higher temperature and longer time resulting in greater substitution degree. Successful modification by acyl groups was evidenced by both fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The modified PG nanoparticles exhibited a more compact structure and homogeneous size distribution, as revealed by transmission electron microscope. Dynamic light scattering measurement indicated that modified PG had a relative larger particle size with a longer chain of anhydride. The contact angle of PG was increased from 40° to 48-96° after modification, indicating significant increase of hydrophobicity. Rheological measurement also indicated that the viscosity of modified PG was increased with the increase of degree of substitution, which was due to the hydrophobic association between nanoparticles. The in vitro simulated gastrointestinal test revealed that the increase of hydrophobicity of modified PG did not significantly improve the stability against enzymatic digestion. But in curcumin encapsulation test, the results showed that modified PG presented higher curcumin loading capacity and encapsulation efficiency compared with native PG. In the meantime, increased antioxidant ability and disappearance of crystalline peaks in X-ray diffraction results indicated the successful encapsulation of curcumin.