Color from Waste: Sustainable Pigment Extraction from Coffee Residues

The exploration of environmentally sustainable pigment sources has become a focal point in contemporary research as industries endeavor to discover alternatives that reduce ecological impact. Among the promising alternatives being examined is the use of coffee residues, which are abundant in bioactive compounds, including pigments [1], [2]. This study focused on the extraction of pigments from coffee pulp using innovative techniques such as microwave- and ultrasound-assisted extraction. The polyphenolic content and antioxidant potential of the extracted pigments were assessed. Extraction was conducted at various pH levels (2, 5, 7, 9, and 12) and ethanol concentrations (100:0, 25:75, 50:50, 60:40, 75:25, and 0:100). The process was performed at different temperatures (30–50 °C) and durations (30, 40, 50, 60, and 70 min). The polyphenolic content of the extracted pigments was characterized using Folin and HCl butanol assays, respectively. The antioxidant potential of the pigments was evaluated using DPPH and FRAP assays. The pigments were characterized using HPLC-MS. The highest concentration of hydrolyzable tannins, at 4.75 mg GAE/g, was achieved with the 60:40 ethanol/water mixture of UAE at 50 °C for 60 min, whereas the aqueous extract with pH 12 at 40 °C for 70 min yielded the highest concentration of condensed tannins, at 12.4 mg CE/g. The condensed tannin content increased with pH. The HPLC-MS analyses revealed the presence of Caffeic acid 4-O-glucoside, 1-Caffeoylquinic acid, 3-Feruloylquinic acid, HHDP-hexoside, 1,3-dicaffeoylquinic acid, 5-heptadecylresorcinol, and cyanidin 3-O-xylosyl-rutinoside. The polyphenolic composition increased with time and temperature. The antioxidant activity of the extracts increased with increasing polyphenolic content. This study highlights the potential of coffee residue-derived pigments as natural colorants. These pigments not only serve as sustainable additives, but may also enhance the shelf life of treated products through their bioactive properties.