A Study on the Stoichiometry of Casein/Chitosan Gel Complexes as a Delivery System for Quercetin

As a well-known plant flavanol, quercetin possesses a diverse range of biological properties. These include its ability to act as an antioxidant, reduce inflammation, and exhibit anticancer effects. Consequently, it finds extensive application in numerous models related to wound healing. However, the poor physicochemical characteristics of the molecule (which include low solubility, stability, and permeability) eventually reduce its bioavailability at the targeted sites. A variety of nano formulations with great therapeutic potential have been created in order to get around these obstacles on the way to successful therapy. The current investigation aims to examine the properties of nano- and micro-sized casein/chitosan gel polyelectrolyte complexes (PECs) with respect to their potential for quercetin loading and release. Four different types of hydrogel particles at pH 6 and different casein/chitosan charge ratios were synthesized; namely, 1:1, 2:1, 4:1, and 6:1 in excesses of casein. The attractive electrostatic interactions between the oppositely charged polyelectrolytes were proved by FT-IR spectroscopy. The process yield increased from 37.5% to 72.5% in excesses of casein. The gel particle’s size varied between 377 nm and 5.72 µm depending on the casein/chitosan stoichiometry. The morphology of the obtained gel polyelectrolyte complexes was found to be spherical, based on scanning electron microscopy and atomic force microscopy analysis. The quercetin loading efficiency was above 95% for all investigated hydrogel complexes. Investigation of the physical state of the loaded polyphenol by the differential scanning calorimetry and X-ray powdered diffraction technique suggested the occurrence of partial recrystallization phenomena. The quercetin release test was performed in phosphate buffer (pH 5.5) at 32 °C and permanent stirring at 50 rpm. A zero-order model was used to describe in the best way the release kinetics. The reported casein/chitosan complexes loaded with quercetin may find application in wound healing as a concomitant treatment.