Development of green methodologies for the analysis of Coffea spp. processing residues

Brazil is the largest coffee producer, with an estimated production of 3.75 million tonnes of coffee grains per year 1. One of the first steps of coffee processing is the removal of its pulp and husk, and it is estimated that about 0.5 and 0.18 tonne, respectively, is generated per ton of fresh coffee 2. Approximately 2,55 million tonnes of these two wastes are generated per year in Brazil, making it a challenge to give a proper destination to these and other by-products. Some natural constituents of coffee fruits are chlorogenic acids, cinnamoyl‐amino and methylxanthines being caffeine the main component 3. This work aimed to investigate the chemical composition of nine different types of coffee-related residues collected in farms and in a major coffee processing company in the region of Botucatu, SP. A green approach was adopt during the whole investigation. After drying and grinding the residues were subjected to 4 types of extraction, in triplicate, using solution EtOH-H2O 7:3 (V/V) in a ratio 1:10 (plant/solvent), namely: (i) dynamic maceration (30 min, T = 30 º C and 1400 rpm); (ii) Vortex-assisted extraction (30 min, T. approx. 25 ºC, 3000 rpm); (iii) Ultrasound-assisted extraction in water bath (10 min, T = 25 ºC); (iv) Extraction in a Italian Moka coffee extractor until full percolation of the material. All hydroethanolic fractions were analyzed in UHPLC-PAD/UV employing water and ethanol as the mobile phase organic modifier. Number of peaks and total area of the chromatogram were the monitored responses. Ultrasound-assisted extraction led to higher average values in six of the nine investigated residues, followed by dynamic maceration (2 residues) and moka (1 residue). The latter showed very good performances in residues that are obtained after roasting process. Analysis of variance (ANOVA) with confidence level of 95% confirmed significant differences between the extraction methods only for two residues. Principal component Analysis (PCA) was performed to compare the chromatographic profiles of the residues under investigation. It was found low variance due to many particularities of the samples, which led to six clusters. A selected sample (a bagasse collected in an extraction company) was subjected to HPLC-PAD/UV-HRMS and HPLC-MS/MS analyses, leading to the identification of mono and di-caffeoylquinic acids and methylxanthines, such as 5-caffeoylquinic acid and caffeine. These compounds exhibit biological properties, such as hepatoprotective 4 and stimulating effect allowing cognitive function to be maintained 5, respectively according to the literature. The green procedure adopted in this work proved to be efficient and that phytochemical investigations of natural complex matrices can be efficiently done while reducing the environmental impact of the experimental procedures. In other words, it can be in line with principles of Green Analytical Chemistry (GAC).