*3.6. SEM Analysis*

The native PUL samples (prior to extraction) and those subjected to extraction with water, the DES synthesized from CC and malonic acid, and the DES synthesized from CC and GA were dried at 60 ◦C for 48 h. The surface characteristics of the samples were observed through a field emission scanning electron microscope (ULTRAPLUS, Carl Zeiss NTS GmbH, Oberkochen, Germany). The effects of different extraction solvents on the surface structure were analyzed.

## *3.7. Antioxidant Activity*

The antioxidant activity of the PUL extracts obtained using the DESs synthesized from CC and different dicarboxylic acids was evaluated using the DPPH assay. DPPH is a stable radical that exists as a purple solution, which turns bile yellow as the free radicals are eliminated by hydrogen or electron donors. The radical scavenging activity was estimated by measuring the change in absorbance [30,31]. L-ascorbic acid was used as a positive control to compare the scavenging activity. DPPH was dissolved in ethanol at a concentration of 100 μM. L-ascorbic acid solutions of 50, 100, and 200 ppm concentrations were prepared, and the samples to be tested were diluted to the desired concentrations. Each test solution (10 μL) was mixed with the same amount of ethanol in a 96-well plate. To each of these solutions, 190 μL of DPPH solution (100 μM) was added. After 30 min of reaction at room temperature, the absorbance was measured at 530 nm using a microplate reader. The DPPH free radical scavenging activity was calculated according to the following equation:

$$AA\% = 100 - \left\lceil \frac{\left(Abs\_{sample} - Abs\_{blank}\right) \times 100}{Abs\_{control}} \right\rceil$$

*Abssample* is the absorbance of the sample in which the extract and the DPPH solution are mixed, *Absblank* is the absorbance inherent in the extract, and *Abscontrol* is the absorbance of the DPPH solution.
