Furfuryl alcohol is a precursor for furfurylthiol in coffee

•The aroma precursor role of furfuryl alcohol was studied by coffee in-bean experiments.•Spiking coffee beans with furfuryl alcohol increased the furfurylthiol levels.•Spiking with labelled d2-furfuryl alcohol produced d2-furfurylthiol upon roasting.•A pathway is suggested passing through furfuryl cation and protein-bound S-furfuryl-l-cysteine. This study investigated the role of furfuryl alcohol (FFA) in the formation of furfurylthiol (FFT), the most important odorant in roasted coffee, using in-bean and spiking experiments. Green beans were spiked with FFA, and after roasting FFT was quantified by stable isotope dilution analysis. The FFT level in the roasted beans increased dose-dependently with addition of FFA. Additionally, beans were spiked with isotopically labelled d2-FFA which generated isotopically labelled d2-FFT after roasting. However, no labelled furfural was observed. The results unambiguously show that FFA serves as a precursor of FFT in coffee. On the other hand, the data indicate that furfural stems not from oxidation of FFA and plays no major role as precursor for FFT formation during coffee roasting. The suggested formation pathway leads from FFA to the furfuryl cation, then protein-bound S-furfuryl-l-cysteine and by subsequent elimination to FFT.