A Chromatographic Study of Some of the Compounds in Roasted Coffee

Abstract

Flavor is the most important factor in coffee from the standpoint of the consumer. It is known that the green coffee itself, its handling, manner of roasting, grinding, storage, method of brewing and handling after brewing, all affect flavor ; yet, an understanding of the chemical nature of flavor and changes in flavor of coffee remains to be found. It was thought that some of the newer chromatographic techniques might be adapted to a study of compounds which might be important in coffee flavor and helpful in determining which substances are native to coffee and which are produced in roasting. There is also the possibility that information on the nature of staling, on flavor changes in boiling brewed coffee, and on some of the more subtle changes in flavor might be found. The methods employed indicated many compounds which have not been identified as yet; some of these are native to coffee and some are produced by roasting. Although some of these compounds are not yet even tentatively identified, the reproducibility and the characteristic nature of the chromatograms indicated the value of the methods developed. Also, the techniques appeared to be applicable to other food. Consequently, this report does not await complete identification of all unknown substances observed. EXPERIMENTAL Non-volatile acids and phenolsMaterials. Roasted Coflee. Unless otherwise specified, the analyses were performed on that coffee obtained from The Coffee Brewing Institute, Inc., and hereafter referred to as standard coffee. Other samples were purchased locally.Green coffee: A ground sample of Santos coffee was used. Chromatographic solvents: Dimethylformamide, cyclohesane, and t-butyl alcohol were technical grades. For heptane, Skellysolve-C was used. All other solvents were reagent grade. None of the solvents was further purified.Procedures. Preparation of estracts: A series of extracts was prepared as follows: Distilled water (500 ml.) was added to ground roasted coffee (100 9.) and the mixture was placed in a refrigerator (2" C.) for 2-3 days. The grounds were removed by filtration, and a second extraction of the same grounds was carried out at 85-90" C.The grounds were again removed and finally extracted with boiling water. Ecah of the above 3 extracts was divided into 2 portions, one of which was acidified and the other made alkaline. The 6 extracts were finally concentrated t o syrups by distillation under reduced pressure. I n addition t o these extracts, acidic and alkaline concentrates of green coffee (extracted at 85-90" C.) were prepared.Paper chromatography. The chromatographic procedure and indicators were essentially those of Buch et al.(3), with iso-amyl alcohol (rather than n-amyl alcohol) constituting the moving solvent.