Tailored nanocellulose structure depending on the origin. Example of apple parenchyma and carrot root celluloses

Cellulose is the major polysaccharide of cell walls in every plant, making it one of the most abundant natural polymers on Earth. However, despite many decades of investigations, the supramolecular structure of cellulose and especially its variation in the cell walls of different plants have still not been fully revealed. In the present study, cellulose from the parenchymatic tissue of apple fruits and carrot roots was isolated, and nanocellulose was further prepared by high-intensity ultrasonication. AFM revealed that the obtained nanocellulose differed in dimension between the two plant species. Compared with carrot cellulose, whose nanocellulose was obtained in the form of whiskers, apple cellulose had longer and thinner nanofibrils. Both nanocellulose types also differed in terms of their crystalline structure. XRD data indicated that, compared with the apple cellulose, the carrot cellulose had a higher degree of crystallinity and larger crystallites. Moreover, FTIR and Raman spectroscopy revealed differences between the cellulose types in terms of their methine environment, hydroxymethyl conformations and skeletal vibrations. Additionally, with respect to their mechanical properties, the less crystalline apple cellulose and nanocellulose films were more elastic than the stiffer carrot cellulose and nanocellulose films. The possible reason for such differences between the two cellulose types is related to differences in plant tissue morphology and function. During development, apple fruit cell walls must withstand increasing turgor, probably higher that in the case of carrot tissue; therefore, the cellulose scaffolding must be elastic and strong. On the other hand, carrot, a root vegetable, also has to be strong enough to penetrate the soil as well as for its own growth; thus, the cell wall and cellulose scaffold have to be stiff and tough. Thus the structure of nanocellulose depends not only on the treatment but also on the cellulose source.