Natural starches suitable for 3D printing: Rhizome and seed starch from Millettia speciosa champ, a non-conventional source

The demand for exploring and investigating novel starches for various applications has been high, yet starches abundant in Millettia speciosa Champ (M. speciose) plants have barely been studied. This study aims to investigate the multiscale structure and physicochemical properties, especially good hot-extrusion 3D printability of M. speciosa starches. MRS (rhizome starch of M. speciose) and MSS (seed starch of M. speciose) exhibited different structure comparing with CRS (cassava starch) and WCS (waxy corn starch), such as smaller granules, higher amylose content, weaker short-range ordered structures and lower crystallinity. MSS exhibited a high R_h,AP2 value of 2.50, the thickest lamellar repeating distance of 10.30 nm and the strongest interconnected structure. Correspondingly, MSS displayed low solubility and swelling power, along with the highest onset gelatinization temperature (T_o), gelatinization enthalpy (ΔH) and resistance starch (RS) content at 75.81 °C, 11.74 J/g and 29.91 %, respectively. Notably, MRS and MSS demonstrated hot-extrusion 3D printability with high printing accuracy(> 93 %) and stability (> 98 %). The significant differences in physicochemical properties between M. speciosa starches are presumed to be influenced by the content of amylose and the length of amylopectin. Starches from M. speciose exhibit potential as thermostable additives and 3D printing materials.