Green and reagent-free synthesis of starch nanoparticles using normal corn starch via pyrolytic self-assembly method

This study developed a pyrolytic self-assembly (PSA) method to synthesize starch nanoparticles (SNPs) from normal corn starch, addressing the scalability limitations of conventional "bottom-up" approaches that rely on chemical reagents or enzymes. The multiscale structural characteristics and self-assembly mechanism of PSA-SNPs were systematically investigated, with particular emphasis on the effects of pyrolysis temperature (170-210 °C) on their physicochemical properties. Although higher pyrolysis temperatures improved SNPs yield, excessive thermal degradation occurred at 210 °C, as evidenced by extensive α-1,6 glycosidic bond cleavage, a substantially increased proportion of short (fa) chains, a sharp reduction in molecular weight (M_w), and the accumulation of acidic and carbonyl groups. These changes led to a broader particle size distribution and pronounced color darkening. In contrast, the optimal pyrolysis temperature of 190 °C favored preferential cleavage of α-1,4 glycosidic bonds, reducing M_w and radius of gyration (R_g) to 1/70th and 1/5th of their original values, respectively, while maintaining chain length distributions comparable to that of native starch. Following pyrolysis treatment, the subsequent hot-water dispersion step disintegrated the granular architecture of the pyrolyzed starch, enabling the release of molecular fragments that self-assemble into micelle-like SNPs through hydrophobic interactions. This distinct assembly mechanism conferred superior anti-retrogradation capability to PSA-SNPs. Compared with the classical nanoprecipitation method, PSA produced SNPs with smaller Z-average size (53.8 vs. 63.7 nm), higher yield (97.5 % vs. 90.7 %), and enhanced hot-water redispersibility (96.2 % vs. 82.4 %). Given its straightforward preparation process, the PSA method represents a novel, reagent-free and industrially scalable route for high-quality SNPs production.