This study focused on improving curcumin stability in various pHs and NaCl concentrations and reducing the strong scent of turmeric by the nanoemulsions system and further coating with water-soluble chitosan (WSC). Turmeric extract-loaded nanoemulsions (TE-NEs) were firstly prepared by mixing an oil phase containing turmeric extract, MCT oil, and lecithin, and an aqueous phase containing tween 80 using an ultrasonication method. TE-NEs were further coated with WSC in the ratio of TE-NEs and WSC (1:1 to 1:10). The optimum WSC-TE-NEs exhibited an average particle size of 182 nm, a PDI of 0.317, and a zeta potential of +30.42 mV when WSC-TE-NEs were prepared in the ratio of 1:1. The stability of the WSC-TE-NEs was also assessed by determining the remained curcumin content. The remained curcumin contents of the TE-NEs and the WSC-TE-NEs were higher than that of the turmeric extract (TE) at pH 2~7 and NaCl concentrations of 100~400 mM. Fourier transform infrared (FT-IR) spectra, transmission electron microscope (TEM), and confocal laser scanning microscope (CLSM) images confirmed that the TE-NEs were successfully encapsulated with a WSC coating. As a result of GC analysis, the content of aromatic-turmerone was significantly decreased in the TE-NEs and the WSC-TE-NEs compared to the pristine TE, but there was no significant difference between the TE-NEs and the WSC-TE-NEs. These results suggest that water-soluble chitosan-coated nanoemulsions may be suitable for improving the chemical stability and masking effect of curcumin to facilitate its application in food.
Keywords: masking effect; nanoemulsion; stability; turmeric extract; water-soluble chitosan.