Hydrodistillation fractions of coffee (green and roasted) and coffee by-product (silver skin and spent grounds) as a source of bioactive compounds

Coffee silver skin (CSS) and spent coffee grounds (SCG) produced during green coffee roasting (GC) and roasted coffee brewing (RC) are usually disposed of into the environment. In search of alternatives for their use in the form of hydrolates and water residues obtained by hydrodistillation, this work examines their analysis by GC-MS and UPLC-MS2 for bioactive compounds, in addition to GC and RC. The results show that the proportions of volatile compounds in the hydrolates are different, so that each hydrolate has a unique composition, which is crucial for further use. GC and ground GC contained phenols, aldehydes, alcohols, and ketones, while RC and ground RC contained pyrazines, phenols, aldehydes, and furans. Aldehydes (21.45 and 47.56%, respectively) and caffeine (15.13 and 11.65 mg/L, respectively) predominated in the hydrolates from CSS and SCG. Hydrolates from RC had the highest levels of caffeoylquinic acids, followed by CSS and SCG. The GC water residues contained the highest amounts of caffeoylquinic acids, with 5-caffeoylquinic acid (399.02 mg/L) dominating along with 3-p-coumaroylquinic acid, caffeic acid, and p-coumaric acid. Thus, it can be emphasised that the hydrodistillation fractions are a valuable substrate for the isolation of bioactive compounds and should be further investigated for their future potential applications.