Background. Grounds generated during coffee brewing as waste produced in the world in millions of tons per year seem to be an interesting source of bioactive substances for further use. The aim of the study was to evaluate the content of bioactive components in coffee grounds obtained from coffee brewing using popular methods. Coffee grounds obtained as a result of brewing Arabica coffee using five methods: pouring, drip, crucible, coffee maker and espresso machine were tested. The content of phenolic acids and total phenols, as well as antioxidant activity (by means of DPPH• and FRAP methods) and caffeine (for the first time by means of high-performance thin layer chromatography (HPTLC) technique) were assessed.
Results and conclusion. A coffee brewing method significantly affects the residue of bioactive compounds in grounds. The results obtained allow to conclude that the methods in which the contact of a ground grain with water is short, and a grain is coarsely ground, leave the most polyphenols and caffeine in coffee grounds. Such techniques were those using a drip and espresso machine (total phenolic content up to 12.29 and 14.88 mg gallic acid equivalents/g, respectively) and pouring in the case of caffeine (21 mg/g). In turn, coffee grounds obtained from brewing coffee in a crucible, in which most of the determined substances were extracted into the infusion, had the least bioactive compounds. Out of all the extraction systems being evaluated, aqueous ethanol (50 %) was indicated as the most effective one. The use of spent coffee grounds as a source of bioactive substances may be a valuable way to valorize large amounts of gastronomic waste.
antioxidant activity, brewing methods, caffeine, coffee grounds, HPTLC