Design of a Smart Hydroxypropyl Methylcellulose (HPMC) Film and Red Cabbage (Brassica oleracea var. capitata f. rubra) Extract as a Quality Indicator in Rural Cheese

Through the development and application of a biodegradable film based on a commercial polymer such as hydroxypropyl methylcellulose with the addition of anthocyanin extract extracted from red cabbage ( Brassica oleracea var. capitata f. rubra ) as a pH indicator agent. The extraction of anthocyanins was carried out using an acidified solvent with an ethanol (70%)—HCl (0.1 M) solution at 80% (v/v), which was mixed with red cabbage powder at ratios of [1:10], [1:15], [1:20] (m/v). Undesired components were removed through vacuum filtration, centrifugation, and precipitation separation. The red cabbage anthocyanin extract (RCAE) was quantified by the differential pH method and characterized using UV–Vis and Fourier transform infrared spectroscopy (FTIR). Based on the total anthocyanin content (TAC), a working extract E3 [1:20] (m/v) was selected as it presented the highest TAC value with 46.78 ± 0.49 mg Cy3G/L. The films were prepared by casting using a standard formulation as a control (C), and the solvent content was replaced with RCAE at 10%, 20%, and 30% for each formulation. The films were characterized by measuring their water interaction properties, optical and structural properties using UV–Vis, FTIR, Colorimeter, Glossmeter, scanning electron microscope, and optical microscopy analysis. Finally, the film was applied to a food matrix (queso costeño, a fresh rural cheese typical of the Colombian Caribbean region), and physicochemical parameters such as pH, acidity, and color were measured over a total storage time of 12 days at 4°C. Additionally, the food matrix was microbiologically analyzed for deterioration through the viable mesophilic aerobes, molds and yeasts, and total coliforms count. The reaction of the film, which had its color measured on the working days, showed a significant change (∆ E ≥ 5), demonstrating the film's ability to indicate the pH of the food.