Effect of phosphorylated modification on natural inulin: structural characterisation and gel properties

To improve the gel properties of natural inulin (FI), in this study, FI was phosphorylated to prepare natural inulin phosphodiester (PDFI). The structures of FI and PDFI were characterised by Fourier transform infrared spectroscopy (FTIR), particle size and scanning electron microscopy. FI and PDFI gels (mass fraction 20%–40%) were prepared and stored for 0–7 days to study their effects on water-holding capacity, rheology and texture properties. The FTIR spectra showed absorption peaks of P-O-C and P=O bonds, indicating that some hydroxyl groups were replaced and phosphorylation was successful. Compared with FI, the specific surface area of PDFI was increased 7.7-fold and the microstructure was smoother. When the fraction of PDFI was 35%, the water-holding rate of PDFI gel was 21.2%, 23.3%, 19.7%, 19.1% and 19.3% higher than FI gel at different storage time, respectively. PDFI gel with higher mass fraction (25%–40%) had lower hardness. Rheological analysis showed that PDFI gels had stronger viscoelastic and solid-like properties. These results reveal native inulin phosphorylation improved gel properties.