Comparison of morphology and rheology of starch nanoparticles prepared from pulse and cereal starches by rapid antisolvent nanoprecipitation

Starch nanoparticles (SNPs) were produced from pulse (faba bean and field pea) and cereal (corn and wheat) starches by rapid nanoprecipitation under identical conditions. SNP morphological features such as shape and particle size distribution (PSD) were determined by field emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS) techniques. Static and dynamic rheological properties of the aqueous SNP suspensions were investigated by rotational and oscillatory rheometry. The SNPs from all starch sources were spherical in shape but varied in their size distribution. The viscosity and viscoelastic behavior of SNP suspensions when determined as a function of shear, frequency and temperature were dependent on starch source and SNP concentration. The SNP suspensions exhibited a viscous liquid-like behavior at low concentrations (i.e., 1% w/v), but an elastic gel-like behavior at high concentrations (i.e., 5% w/v). Interestingly, at a concentration of 5% (w/ v), SNP suspensions showed an excellent flow behavior, demonstrating their capacity to instantaneously recover from the applied shear deformation. However, pulse SNPs displayed relatively greater viscosities and a more elastic behavior than cereal SNPs, indicating their potential to form extensive inter-particulate associations. A schematic diagram has been proposed to explain the observed rheological behaviors, predicting inter-particulate network formation at room temperature and the biphasic molecular network formation during heating of aqueous SNP suspensions. A careful selection of starch type and processing conditions, such as temperature and shear conditions, is required to achieve specific desired functionalities for SNP in the food industry.