Coffee pulp is one of the most abundant residues in the coffee agroindustry. Its inadequate handling and disposition produce contamination of water and soil. However, this waste contains high levels of tannins and other phenolic compounds, which could be extracted, getting added value. A vertical rotational composite design was used to optimize procedures for obtaining total polyphenols and tannins, based on temperature and concentration of sodium hydroxide in the extraction solution, at a fixed time of 30 minutes of contact. The optimal values for the extraction of total polyphenols were obtained at a temperature of 55.8°C, using sodium hydroxide solutions of 2.55 M, achieving the extraction of 116.59 mg GAE/g (mg of gallic acid equivalent per gram of pulp). These values are significantly higher than those reported in other studies. The optimum conditions for the extraction of tannins were a maximum temperature of 64.14°C for the test and concentrations of sodium hydroxide of 2.58 M, which obtained the extraction of 66.07 g GAE per gram of pulp in tannins. Most favorable values for antioxidant capacity were close to those obtained for both polyphenols and tannins. The increase in the concentration of sodium hydroxide of the extraction solution above 2.7 M caused the reduction of the contents of total polyphenols, and tannins. Results show the possibility of valorizing coffee pulp by extracting tannins and other polyphenols and reveal possible uses of process streams. These would allow the formulation of strategies framed within the concepts of green chemistry, circular economy and biorefineries.
Keywords: tannins, antioxidant capacity, alkaline extraction, DPPH assay,