Effect of melting point and drying technique on encapsulation of hydrophobic active compounds by coprecipitation with starch nanoparticles

This study aims to optimize the coprecipitation method for the encapsulation of hydrophobic active compounds using starch nanoparticles (SNP). Saturated fatty acids with varying chain lengths (8, 18, and 22) were used as model compounds. Differential scanning calorimetry analysis revealed that various reaction conditions influenced the encapsulation efficiency of fatty acids, with 30% ethanol, an addition level of 10 mg/mL, heating for 30 min, and a cooling rate of 10 k/min, producing the highest melting enthalpy of the shifted thermal transition peak. Specifically, heating near the melting point of the guest compound resulted in substantial structural modifications between the guest compound and the SNP. D-δ-tocopherol, coenzyme Q10, and curcumin were then encapsulated under optimized conditions and dehydrated via spray- and freeze-drying. Transmission electron microscopy, Fourier transform-infrared spectroscopy, and X-ray diffraction analyses revealed that each compound underwent spherical aggregation with SNP in an amorphous state via hydrogen bonding and hydrophobic interactions. Freeze-drying generally resulted in higher encapsulation efficiency than spray-drying. For D-δ-tocopherol and curcumin, freeze-dried composites exhibited higher storage stability under varying pH, UV irradiation, and thermal treatment conditions. However, for coenzyme Q10, spray-drying resulted in higher storage stability.