## 2 Materials and Methods
### Film Characterization  
**Optical and Morphological analysis. ** Images of WFFs with coffee silverskin particles, from Stereo zoom microscope (Kern Optics, Ballingen, Germany), were used to examine the dispersion of particles in the wheat flour matrix. A VIS2.0 Pro microscope was used for particle measurements. The scanning electron microscope utilized for films with coffee silverskin aqueous extracts was FESEM JSM 7610 PIPlus (JEOL) from JEOL in Tokyo, Japan, boasting an instrument resolution of 5 nm. In order to conduct a thorough analysis of the samples, it was imperative that they displayed conductivity. To facilitate this, a thin carbon-layer coating was administered to the samples to improve surface conductivity. **Color measurements. ** Measurements of the colorimetric indicators were performed using a Macbeth CE 3000 spectrophotometer under \(D_{65}\) illumination, 10\({}^{\circ}\) standard observer with ultraviolet (UV) included, and the specular component included. The color intensity of the films was assessed through testing. The Kubelka-Munk equation was utilized to evaluate the color strength (K/S) via a light reflectance technique:  
\[\frac{K}{S}=\frac{\left(1-R\right)^{2}}{2R} \tag{1}\]  
where \(R\) stands for reflectance at the maximum absorption wavelength, \(S\) stands for the scattering the coefficient, and \(K\) stands for the absorption coefficient. Water absorption (WC), Solubility, and Swelling Degree  
To quantify the water content of the films, a sample measuring 1 \(\times\) 1 cm was excised and weighed both before and after undergoing a 24 h drying process in an oven set at 105 \({}^{\circ}\)C. The samples were used after being left for one day in a desiccator with silica gel. The water absorption (%) was calculated by conducting three repeated measurements for each film and applying the specified equation:  
\[\text{Water absorption }(\%)=\frac{M_{o}-M}{M_{o}}\times 100 \tag{2}\]  
where \(M_{o}\) is the initial mass (g) and \(M\) is the bone-dry mass (g). Film specimens of dimensions 1 \(\times\) 1 cm underwent a desiccation process at 70 \({}^{\circ}\)C for 24 h in a vacuum oven to acquire the initial dry weight (\(M_{1}\)). Following this, the films were positioned in 50 mL beakers filled with 30 mL of distilled water, sealed with plastic covers, and stored at 25 \({}^{\circ}\)C for 24 h. Upon completion of the designated time, any remaining water in the beakers was removed, and the residual film specimens were gently dried using filter paper. The residual film specimens (\(M_{2}\)) were subsequently subjected to an additional round of desiccation at 70 \({}^{\circ}\)C for 24 h in a vacuum oven to determine the final dry weight (\(M_{3}\)). Three measurements were conducted for each film specimen to ensure precision and uniformity. Film solubility and swelling degree were computed using the following equations, respectively:  
\[\text{Film Solubility }(\%)=\frac{M_{1}-M_{3}}{M_{1}}\times 100 \tag{3}\]  
\[\text{Swelling degree }(\%)=\frac{M_{2}-M_{1}}{M_{1}}\times 100 \tag{4}\]  
**FT-IR (ATR). ** The Perkin Elmer Spectrum 1 spectrophotometer (Shelton, CT, USA), was used for the analysis. It was outfitted with an attenuated total reflectance (ATR) device and employed thin films for the measurements. Spectra were captured within the 4000-650 cm\({}^{-1}\) range at a 2 cm\({}^{-1}\) resolution, with 32 scans averaged to reduce noise. Spectrum v5.0.1 software was utilized to detect multiple peaks. **Gas Permeability. ** The gas permeability of the films that were prepared was assessed by means of a gas permeability analyzer, model N500 instrument (Guangzhou Biaoji Packaging Equipment Co., Biaoji, China), under the following conditions: a constant temperature of 23 \({}^{\circ}\)C, relative humidity of 0%, and a gas flow rate of 10 mL/min. **Water Vapor Permeability. ** Water vapor permeability was assessed in accordance with the ASTM E96 standard [28]. The experiment used glass Petri dishes filled with 10 mL of distilled water, creating 100% humidity.