Nano-sized Starch: Preparations and Applications

Nano-sized starch is a kind of organic nanoparticles prepared from starch with the size of 50−200 nm, which has been extensively studied these years due to its characteristics of renewability, biocompatibility, low density, and high biodegradability. It can be roughly divided into the categories of starch nanoparticles (SNs) and starch nanocrystals (SNCs) based on its preparation methods and properties; a special distinction is emphasized in this chapter in order to get a better interpretation. Physical, chemical, enzymatic, or the combined methods are involved in the preparation of nano-sized starch and are classified into the top-down and bottom-up protocols, respectively. As the size of starch granules is decreased down to the nanometer scale, both the specific surface area and total surface energy increase. Therefore, a highly reactive surface with a greater number of hydroxyl groups is ready for modification so that new characteristics can be introduced. The strategies of chemical derivatization, “grafting onto,” “grafting from,” and enzyme modification are adopted to improve the dispersity, hydrophobicity, compatibility, or crystallinity of the nano-sized starch. Nano-sized starch or the modified nano-sized starch shows great importance in the applications of fillers, emulsion stabilizer, and delivery vehicles. Other applications such as adsorbents, binders, thermo-responsive materials, templates, biosensors, and biomarkers are receiving increasing attention and also reviewed accordingly. Nevertheless, further research is needed, especially regarding industrial-scale production and the dispersibility and re-dispersibility of powdered products of nano-sized starch.