The effect of annealing and cryoprotectants on the properties of vacuum-freeze dried starch nanoparticles

Starch nanoparticles prepared through high pressure homogenization and mini-emulsion cross-linking technology were successfully vacuum-freeze dried. Annealing process was introduced in the drying process and the cryoprotectants (lactose and mannitol) were used in the sample matrix. The effect of the annealing and cryoprotectants on the moisture content, glass transition temperature (Tg), amorphous/crystalline nature, particle size, morphology and the redispersibility of these nanoparticles was investigated. The residual moisture content of the nanoparticles was 4–9% (w/w) and it was lower in samples which were unannealed and contained cryoprotectants. Mannitol as cryprotectant resulted into starch nanoparticles with uniform spherical shape. The Tg of these nanoparticles varied from 52 °C to 57 °C and the difference was due to annealing and cryoprotectants. The annealing process and the presence of cryoprotectant did not hugely affect the X-ray diffraction pattern and FT-IR spectra which revealed the fully cross-linked and amorphous glassy state of starch nanoparticles.