Production of starch nanoparticles using normal maize starch via heat-moisture treatment under mildly acidic conditions and homogenization

• The starch nanoparticles (<50 nm) were prepared via combination of the HMT under mildly acidic condition and homogenization.
• Over 80% of starch substance was recovered as nanoparticles.
• The treatment time for the starch nanoparticle was reduced relative to traditional acid hydrolysis processes.

Normal maize starch was subjected to heat-moisture treatment (HMT) under mildly acidic conditions (0.000, 0.050, or 0.075 M H2SO4) for various treatment times (3, 5, or 8 h) followed by homogenization up to 60 min to prepare nanoparticles. The combination of HMT (0.075 M, for 8 h) and homogenization (60 min) produced nanoparticles with diameters of less than 50 nm at a yield higher than 80%. X-ray diffractometry and size-exclusion chromatography revealed that HMT under mildly acidic conditions selectively hydrolyzed the starch chains (especially amylose and/or long chains of amylopectin) in the amorphous region of the granules without significant damage to the crystalline structure, however, modification of the molecular structure in the amorphous region increased fragility of the granules during homogenization. Homogenization for 60 min caused obvious damage in the long-range crystalline structure of the HMT starch (0.15 N, for 8 h), while the short-range chain associations (FT-IR) remained intact.