ANTIMICROBIAL AND ANTIOXIDANT POTENTIAL OF COFFEE HUSKS FERMENTED WITH LEMON PEEL

The study of natural compounds found in Brazilian plants with antimicrobial potential is one of the alternatives to replace the use of chemical preservatives and prevent antibiotic resistance. With this objective, the antimicrobial potential, total phenolic quantification, and antioxidant potential of three samples of dried coffee husks fermented for 36 hours were evaluated. The extracts from coffee husks fermented with kaffir lime peels (C1), coffee husks fermented with Sicilian lemon peels (C2), and coffee husks fermented without the addition of lemon peels (control – C3) were obtained by weighing in an Erlenmeyer flask and adding 80% ethyl alcohol in a 1:10 ratio. After weighing, the Erlenmeyer flasks were placed in an ultrasound water bath for 50 minutes at a frequency of 45 kHz, a power of 50%, and a temperature of 40 ºC. The solid part was discarded, and the liquid part was centrifuged at 5000 rpm for 20 minutes. The supernatant was rotary evaporated, sterilized using a 0.45 µm membrane, and frozen until use. Three pathogenic microorganisms, Escherichia coli ATCC 11229, Salmonella enteritidis ATCC 13076, and Staphylococcus aureus ATCC 25923, were incubated in BHI broth at 37 ºC for 24 hours. Then, pathogenic cultures (100 µL), extracts (100 µL), and double-concentration BHI broth (100 µL) were added to a 96-well Elisa plate. This plate remained incubated for 24 hours at 37 ºC in an Elisa reader and Multiskan SkyHigh microplate photometer – Thermo Fisher Scientific. Readings were taken every 2 hours at an absorbance of 600 nm. The total phenolic results were obtained using the standard curve of gallic acid, with readings performed in a spectrophotometer at 760 nm. The total phenolic results, expressed in gallic acid, were higher for the samples fermented with lemon: 115.08 ± 10.09 mg/100 g (C1), 125.66 ± 3.75 mg/100 g (C2), and 80.80 ± 2.13 mg/100 g (C3). The antioxidant capacity, measured by the ABTS and FRAP methods, showed greater potential in samples with the addition of lemon peel. Regarding antimicrobial potential, all samples showed inhibition of the growth of pathogenic microorganisms. This study demonstrated that extracts from dried fermented coffee husks, with or without the addition of lemon peel, exhibit antimicrobial potential against the tested pathogenic microorganisms. Further analyses, such as minimum inhibitory concentration and identification of the active inhibitory compound, are underway to elucidate the inhibition mechanism.