Effects of different extraction methods on the phenolic profile, antioxidant and antimicrobial activity of the coffee grounds and coffee silverskin (Coffea arabica L.)

Abstract

Background

During coffee processing, a large volume of waste is generated. This study investigated the phenolic profile, antioxidant and antibacterial activity of coffee grounds and silverskin using different extraction methods.

Results

Ultrasound-assisted extraction (UAE), enzyme-assisted extraction (EAE), and ultrasound-assisted enzyme extraction (UAEE) were effective for extraction of polyphenols, with UAE being the method that promoted the highest extraction of polyphenols. The coffee ground and coffee silverskin extracts showed high antioxidant capacity for the three methods ABTS, DPPH, and ORAC (4013.36–3241.89 μmol Trolox/g; 1.82–2.06 IC₅₀ μg/mL; and 26.60–16.20 μmol Trolox/mL, respectively). The phenolic profile demonstrated that most of the compounds in both matrices were chlorogenic acid, caffeic acid, 2,4-DHBA, 2,5-DHBA, and 3,4-DHB. EAE promoted a greater release of polyphenols in the coffee ground (2676.42 μg/g), while UAEE was more effective for the coffee silverskin (2111.54 μg/g). The Principal Component Analysis grouped the samples according to the extraction method, based on their content and phenolic potential, for coffee ground and coffee silverskin. As for antibacterial activity, the most expressive result was for Gram-positive bacteria. For both matrices, when extracted by the UAEE method, they presented the minimum inhibitory concentration to inhibit the growth of Bacillus subtilis, Bacillus cereus, and Listeria monocytogenes.

Conclusion

The extraction methods used are environmentally safe alternatives, enabling the reuse of natural compounds and contributing to the circular economy, seeking to transform waste into raw material for the extraction of compounds of interest and possible subsequent application in agriculture as biofertilizers or bioherbicides.