How does phytoglycogen loading improve curcumin solubility?

Curcumin

Curcumin (CCM) is a polyphenolic compound extracted from turmeric plants such as Curcuma longa, Curcuma longa, Ulmoides, etc. It is a natural edible yellow pigment allowed to be used both at home and abroad.
Meanwhile, CCM has various physiological and pharmacological activities, such as antibacterial, antitumor, anti-human immunodeficiency virus effects, antifibrotic effects, etc. It is heat-resistant and safe (no obvious toxic side effects on human body at the dose of 12g/d).
However, the water solubility of CCM is very low (11 ng/mL, 25°C), which leads to its poor absorption and low bioavailability in the body, and its application in the related fields such as food and medicine with water-soluble matrix is thus greatly limited. Therefore, improving the water solubility of CCM is the key to develop its potential application value.
Currently, methods to improve the solubility of CCM include a variety of techniques or systems based on liposomes, micelles, nanoemulsions, amorphous solid dispersions, chemical modification of CCM, and the formation of complexes, with carrier materials that include natural polymers (carbohydrates, proteins, and fats) as well as synthetic polymers.
However, most of the above methods are not easily applicable to food products, e.g., a large number of surfactants are required for liposome preparation; most of the natural polymers need to be modified, and synthetic polymers are usually of low biocompatibility. There are also problems of complicated preparation process and high cost.
Phytoglycogen
Phytoglycogen (PG) is a highly branched soluble α-D-glucan linked by α-1,4 and α-1,6 glycosidic bonds. Due to the short average chain length, high degree of branching, and the structural features such as tight outer and loose inner dendritic branching pattern, and small particle size, a large number of glucose residues are present on the surface of the molecule, and it is soluble in cold water due to the formation of hydrogen bonds with water molecules. It can form hydrogen bonds with water molecules and is easily soluble in cold water.
Studies have shown that PG does not contain a cluster structure, but forms a spherical structure with more and shorter branches and a tighter structure than branched starch, making it a natural nanoparticle.
Chen et al. loaded lutein and quercetin with PG and significantly increased the apparent solubility of lutein (0.56 μg/mL increased to 130.65 μg/mL) and quercetin solubility (4.32 μg/mL increased to 241.76 μg/mL). In this study, based on the characteristics that PG is easy to be dispersed and dissolved in cold water and has good dispersion stability, a certain amount of ethanol solution of CCM with high concentration was added to a certain concentration of aqueous PG solution using PG as the carrier, which made the system supersaturated with CCM.
Some of the free CCM molecules interacted with PG to form a phytoglycogen-curcumin (PG-CCM) complex, which improved the apparent solubility of CCM.
Conclusion.

PG is a novel nanoparticle carrier that loads CCM in a self-assembled manner to form PG-CCM complex nanoparticles. The loading method was simple and easy without any additives, and the apparent solubility of CCM could be increased about 2700-fold after loading.
PG and CCM may interact with each other through intermolecular hydrogen bonding, and there is no significant change in the particle size of PG loaded with CCM, with an average particle size of 70-75 nm, in which CCM exists in an amorphous and non-crystalline state in the PG-CCM complexes, and hydrogen bonding is the main force for the interaction between the CCM and carrier PG, and the CCM is shifted from the microenvironment of larger polarity to the region of smaller polarity in which the PG interacts.
Our results suggest that PG is an efficient carrier that can significantly increase the apparent solubility of CCM, and the PG-CCM complex is simple to prepare and is expected to be incorporated into functional foods to promote the pharmacological effects of CCM.