Fabrication of citric acid-modified starch nanoparticles to improve their thermal stability and hydrophobicity.

Starch nanoparticles (SNPs) were reacted at 130 °C for 1.5 h in the presence of citric acid (30 %) to enhance their thermal stability and hydrophobicity. Citric acid content in SNP was controlled by washing with different concentrations of ethanol (95 %, 70 % and 60 %) for 2, 5 and 10 min and then subjected to heat treatment at 130 °C. After the modification, the peak at 1732 cm-1 representing ester bond was observed via FT-IR, and the intensity of the peak was decreased with a lower ethanol content in washing medium. For the 60 % ethanol condition, the granular structure was promptly fragmented into particles less than 50 nm in the aqueous solution. The modification enhanced the thermal stability and hydrophobicity of the SNPs. The modified SNPs was used as a nano-vehicle wall material for encapsulating beta-carotene as a model hydrophobic material. Approximately 80 % beta-carotene was encapsulated in the modified SNPs.