Spontaneous assembly of macromolecules in sour cherry (Prunus cerasus L.) fruit into nanocomplexes under cell disrupting conditions

Homogenization of sour cherry fruit in aqueous or alcoholic medium resulted in spontaneous assembly of cell wall components such as pectin, oligosaccharides linked to proteins, polyphenols and malic acid into spherical nanoparticles. These were detergent resistant, uniform spherical structures ranging in size from 25 to 50 nm in solution and appear enlarged when dehydrated into a powder. A different type of nanostructure resembling fibers, ∼5 nm in width, and several micrometers in length, was also isolated from ethanol-bleached cherry devoid of anthocyanins. The nanoparticles could be completely disrupted by treating them with polygalacturonase, indicating the presence of pectin among the constituent molecules. Also, treatment with cellulase and trypsin resulted in the removal of the outer fibrillar structures of the nanoparticles exposing an inner core. Both nanoparticles and nanofibers showed strong affinity to anti- arabinogalactan-protein complexes, and a far lower affinity to anti-extensin. The nanoparticles did not react with anti-homogalacturonan, while the nanofibers showed a very strong reaction. FT-IR spectra of the nanoparticles and the nanofibers showed absorption peaks characteristic to those of proteins and pectin. Both nanoparticles and nanofibers were internalized by cultured human cells efficiently. Treatment with nanofiber-paclitaxel adducts caused cytotoxicity in multidrug resistant colorectal cancer cells, suggesting that nanofibers may have applications in delivering bioactive molecules and materials with therapeutic potential into human cells.