Abstract: To investigate the effects and mechanism of Rhodomyrtus tomentosa polysaccharides (RTP) on the starch properties of Eleocharis dulcis, this study examined the effects of adding different concentrations of RTP to E. dulcis starch (EDS) solution on the gelatinization characteristics, thermodynamic properties, gel properties, and water distribution. The results showed that as the concentration of RTP increased, the peak viscosity, breakdown value, retrogradation value, and gelatinization temperature of EDS decreased, while its thermal stability increased. Moreover, the gelatinization enthalpy reached its maximum level at 0.1% RTP concentration. Low concentration of RTP (0.05%) had no significant effect on the hardness, gel strength or viscosity of EDS gels, while 0.1%–0.2% RTP significantly enhanced the gel strength and chewiness. Scanning electron microscopic (SEM) observation showed that RTP addition transformed the microstructure of EDS gels from disordered porous to honeycomb-like, and the pore wall became thicker with increasing RTP concentration. Low-field nuclear magnetic resonance (LF-NMR) analysis showed that RTP addition resulted in an increase in the proportion of bound water and a decrease in the proportion of free water. Fourier transform infrared spectroscopic (FT-IR) analysis showed that addition of 0.1% RTP caused changes in the vibration characteristics of functional groups in EDS. The X-ray diffraction (XRD) results showed that addition of 0.1%–0.15% RTP promoted the crystallization of EDS, while addition of 0.2% RTP destroyed the crystalline structure. In conclusion, addition of an appropriate amount (0.1%) of RTP can improve the thermal stability and gel strength of EDS, while excess RTP could destroy its crystalline structure. These findings provide a theoretical basis for the application of R. tomentosa polysaccharides in E. dulcis starch-based foods.

Key words: Rhodomyrtus tomentosa; polysaccharides; Eleocharis dulcis starch; gelatinization properties; water distribution; gel properties