Utilization of protein nanoparticles to improve the dispersibility, stability, and functionality of a natural pigment: Norbixin

Abstract

Norbixin is a natural plant-based pigment that can be used to replace synthetic yellow colorants in foods and other products. It is also being explored as a nutraceutical in functional foods and supplements due to its beneficial biological activities. However, the low-solubility and chemical instability of norbixin currently limit its application in many food products. In this study, the potential of biopolymer nanoparticles assembled from food proteins derived from either animal (sodium caseinate (SC) or whey protein isolate (WPI)) or plant (soy protein isolate (SPI)) sources to encapsulate and protect norbixin was examined. The encapsulation efficiency, loading capacity, size, charge, and interactions of the norbixin-loaded nanoparticles were characterized. All protein nanoparticles could successfully encapsulate and protect norbixin, with loading capacities of 26.8%, 31.5% and 17.0% for SC, WPI and SPI, respectively. Fluorescence, infrared spectroscopy, and X-ray diffraction measurements confirmed that norbixin was trapped within the protein nanoparticles in an amorphous form and that hydrogen bonding occurred between the norbixin and protein matrix. The ability of the norbixin-loaded protein nanoparticles to resist environmental stresses (heat, light exposure, and long-term storage) was ranked according as follows: SPI > SC > WPI. The possibility of using norbixin-loaded SPI nanoparticles as plant-based yellow pigments in cheese production to inhibit the leakage of norbixin into whey was also demonstrated. In summary, this study shows that protein nanoparticles can enhance the water-solubility and stability of norbixin, which may extend the application of this natural pigment in foods.