Bottom-up synthesis of amorphous starch nanoparticles via dry-heat pyrolysis and hot-water dispersion

Pyrolytic self-assembly (PSA) was developed to synthesize starch nanoparticles (SNPs). • PSA eliminates enzyme and chemical dependence of traditional bottom-up methods. • PSA produces amorphous, micelle-like SNPs via hydrophobic self-assembly. • PSA at 170 °C achieves 96.93% yield of SNPs with Z-average size of 72.56 nm. • PSA-SNPs show exceptional cold-water redispersibility and anti-retrogradation ability. This study developed a pyrolytic self-assembly (PSA) method that produces starch nanoparticles (SNPs) through a two-step physical processing. Waxy corn starch underwent dry-heat pyrolysis at 170 °C to fragment amylopectin, followed by hot-water dispersion to release the molecular fragments that spontaneously self-assembled into amorphous SNPs via hydrophobic interactions. The resulting SNPs exhibited high cold-water redispersibility (93.3%) and enhanced anti-retrogradation capability. Although increasing the pyrolysis temperature (150–210 °C) improved SNP yield, temperatures exceeding 190 °C caused excessive molecular degradation, characterized by sharp declines in molecular weight, increased proportion of short-chain amylopectin branches (DP 6–12), extensive α-1,6 glycosidic bond cleavage, and elevated acidic and carbonyl content, leading to broader particle size distributions and pronounced color darkening. The optimal pyrolysis temperature of 170 °C yielded 96.9% SNPs with an average particle size of 72.6 nm. The PSA method eliminates dependence on chemicals or enzymes required by conventional bottom-up approaches, offering a scalable route for industrial SNP production. Download: Download high-res image (350KB) Download: Download full-size image