Isolation of micro- and nano-crystalline cellulose particles and fabrication of crystalline particles-loaded whey protein cold-set gel

Micro- and nano-crystalline cellulose (MCC and NCC, respectively) particles isolated from cellulose filter papers via acid digestion were characterised and loaded into a heat-denatured whey protein isolate (WPI) solution which was subsequently cold-set-gelled. Both the MCC and NCC particles were rod-shaped and had higher crystallinity degrees than had the cellulose source they were isolated from. The hydrodynamic diameter of NCC particles was ≈15 nm. Fourier transform infrared (FTIR) spectroscopy suggested more surface hydroxyl groups on the NCC than the MCC particles and complete digestion of hemicellulose on the cellulosic substrate by acid. MCC- and NCC-loaded WPI gel matrices were topographically less uniform and contained many more undulations in comparison to the crystal-free counterpart. It was found, using dynamic rheometry and penetration tests, that the crystal loading into WPI gels weakened the texture. Non-covalent interactions between the cellulose crystals and whey protein strands were proposed in the gel structure according to FTIR results.