*Polyquercetin and Quercetin Copolymers and Antioxidant Properties*

Similar to quercetin, polyquercetin has superior antioxidant properties, depending on the synthetic route and ingredients. A facile and scalable micro-emulsion polymerization/crosslinking technique was developed by Sahiner [82], involved reacting quercetin molecules with glycerol diglycidyl ether (GDE) in the presence of l-α lecithin and cyclohexane, which act as the surfactant and organic phase, respectively. The process was proven to be useful in the synthesis of polyquercetin and quercetin copolymers with customizable antioxidant properties. In contrast to the methods proposed by Sahiner [82], Pivec et al. [83] explored an alternative technique comprising 0.5 g of flavonoid rutin (RU) hydrate in ultra-pure water. The mixture was subjected to enzymatic polymerization through the incorporation of Trametes Versicolor-based laccase (500 mg). The mixing was performed at room temperature, away from UV light for 24 h, after which ammonium sulfate was incorporated to enhance the precipitation process; this was followed by centrifugation, removal of the supernatant solution, and dialysis. A comparison of the two techniques shows that the microemulsion polymerization/crosslinking technique developed by Sahiner [82] was more facile and scalable compared to the lengthy procedures undertaken by Pivec et al. [83]. The focus on the synthetic route is grounded on the chemical structure–antioxidant activity relationship discussed in the preceding sections [77–79,82–85].

In contrast to quercetin molecules, which have found broad applications in targeted drug delivery and food packaging, polyquercetin has mainly been used as an electrode component for glass carbon electrodes modified by multi-walled carbon nanotubes; this was the case in studies conducted by Ziyatdinova et al. [84,85]. In both studies, the oxidation potentials of polyquercetin influenced the chronoamperometric determination of the antioxidant capacity and the quantification of gallic acid, catechin, and epigallocatechin gallate (EGCG) [84,85]. The variable industrial applications of quercetin and polyquercetin demonstrate the influence of polymerization and the choice of the crosslinking method.
