Hydrothermal Treatment Modifies the Chemical Profile of Coffee Pulp ( Coffea arabica ) Extracts and Improves Their Antibacterial Activity against Xanthomonas and Ralstonia

Coffee pulp is an abundant agro-industrial residue whose bioactive compounds could contribute to integrated valorization strategies. This study evaluated the in vitro antibacterial activity and chemical profiles of methanolic extracts from untreated and hydrothermally treated coffee pulp against bacteria of the genera Xanthomonas and Ralstonia associated with crops in Costa Rica. Coffee pulp was treated at 170 °C for 1 or 3 h, and the resulting solid residues were subjected to ultrasound-assisted extraction with 50% (v/v) aqueous methanol. After concentration, the extract obtained after 1 h of hydrothermal treatment showed the highest total polyphenol content (2,100 ± 300 mg of gallic acid equivalents per gram of dry biomass), whereas the extract obtained after 3 h exhibited the greatest inhibition against Xanthomonas (68 ± 5%) and Ralstonia (90 ± 7%), compared with 57 ± 7% and 58 ± 10%, respectively, for untreated coffee pulp. Chemical profiling by high-performance liquid chromatography coupled to high-resolution mass spectrometry indicated glycosylated flavonoids and triterpenes in untreated pulp extract, whereas the hydrothermally treated samples contained phenolic aldehydes, indoles, oxylipins, and amphiphilic lipids, which may be associated with their greater inhibitory activity. These findings show that hydrothermal treatment modified the chemical profile of coffee-pulp extracts and increased their inhibitory activity against Xanthomonas and Ralstonia, highlighting its potential as a pretreatment for the valorization of this agro-industrial residue.