Structure-function relationships of pearl millet nano-starches prepared by different methods

In this study, starch nanocrystals (SNCs) and starch nanoparticles (SNPs) were developed from two pearl millet varieties (HHB 67 and ProAgro 9444) using acid hydrolysis (AH), ultrasonication (US), acid-assisted ultrasonication (AHUS), and gamma irradiation (GI). The obtained nano-starches were characterized and compared with native starch for particle size, zeta potential, morphology, functional properties, thermal stability, structure, pasting, and rheology. The median particle size ranged from 100 to 200 nm, with stable zeta potential values (-12 to -31.2 mV). Morphology revealed spherical particles with some aggregation. Swelling and solubility varied due to depolymerization and chain disruption. AH and AHUS samples showed higher thermal stability, attributed to tighter packing and stronger bonding, while US and GI samples exhibited reduced stability from granule damage and greater water penetration. X-ray diffraction confirmed an A-type pattern for all samples, with crystallinity increasing in AH and AHUS (21.43-37.47 %) and decreasing in US and GI (21.43-16.22 %). FTIR spectra were similar to native starch but with intensity variations. Pasting analysis indicated Type A behaviour for native, US, and GI samples, while AH and AHUS displayed Type D with restricted swelling. All samples exhibited shear-thinning, and US-SNPs uniquely showed weak gel-like behaviour due to molecular entanglements.