title: Screening of raw coffee for thiol binding site precursors using "in bean" model roasting experiments.
abstract: The purpose of the following study was to investigate the influence of coffee roasting on the thiol-binding activity of coffee beverages, and to investigate the potential of various green bean compounds as precursors of thiol-binding sites by using promising "in bean" model roast experiments. Headspace gas chromatographic analysis on coffee brews incubated in the presence of the roasty-sulfury smelling 2-furfurylthiol for 20 min at 30 degrees C in septum-closed vessels revealed that the amounts of "free" thiol decreased drastically with increasing the roasting degree of the beans used for preparation of the brews. A half-maximal binding capacity (BC(50)) of 183 mg of 2-furfurylthiol per liter of standard coffee beverage was determined for a roasted coffee (CTN value of 67), thus demonstrating that enormous amounts of the odor-active thiol are "bound" by the coffee. Furthermore, biomimetic "in bean" precursor experiments have been performed in order to elucidate the precursor for the thiol-binding sites in the raw coffee bean. These experiments opened the possibility of studying coffee model reactions under quasi-natural roasting conditions and undoubtedly identified chlorogenic acids as well as thermal degradation products caffeic acid and quinic acid as important precursors for low-molecular-weight thiol-binding sites. In particular, when roasted in the presence of transition metal ions, chlorogenic acids and even more caffeic acid showed thiol-binding activity which was comparable to the activity measured for the authentic coffee brew.
authors.affiliation: Institut für Lebensmittelchemie, Universität Münster, Corrensstrasse 45, D-48149 Münster, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Müller
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofmann
mesh_terms: D001665:Binding Sites; D002726:Chlorogenic Acid / Q000032:analysis; D002849:Chromatography, Gas; D040503:Coffea / Q000737:chemistry*; D005511:Food Handling / Q000379:methods*; D005663:Furans / Q000032:analysis; D006358:Hot Temperature; D009812:Odorants / Q000032:analysis; D012639:Seeds / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000032:analysis / Q000378:metabolism*
chemical_list: D005663:Furans; D013438:Sulfhydryl Compounds; C455106:furfuryl mercaptan; D002726:Chlorogenic Acid