The chemistry of flavor development during the roasting of coffee is not well understood. Acidity is often considered an important factor in the flavor of brewed coffee. Consequently, a study of the acidic compounds of coffee might contribute to a better understanding of the taste and flavor of coffee beverages. Kaufman (8) made water extracts of both green coffee and successive samples withdrawn during roasting, and observed that the p H fell about one pH unit, and then began to rise. These changes were confirmed here. The optimum roast is often considered to terminate shortly after the p H of the water extract begins to increase. The titratable acidity is nearly doubled at this point (12,16). Kaufman (8) suggested that these changes were due to the formation and volatilization of acetic acid from decomposition of sugars, decarboxylation of acids formed by rearrangement of sugars and decarboxylation of chlorogenic acid. In a heavy roast approximately 50% of the original chlorogenic acid was reported to be destroyed (14). Since partition chromatography on silica gel was particularly adaptable for a separation of organic acids in coffee (9,11,19) a quantitative study of several organic acids in coffee during roasting has been carried out. EXPERIMENTALCoffee samples were obtained from the Coffee Brewing Institute, New York. The samples were vacuum packed in one-pound cans as whole beans and stored at -20" C. Table 1 describes the samples and gives the code.Methods. The weight of 100 beans was obtained as a mean value, weighing 4 groups of 200 beans each. One hundred grams of coffee beans were ground coarsely with a laboratory mill. Moisture was determined by drying 2 g. for 5 hours at 105'-110" C. Thirty-gram samples were shaken 5 minutes with 400 ml. distilled water of 95" C. in a 1000-ml. Erlenmeyer flask. Next, 100 nil. of distilled water was added by rinsing the walls of the flask; the flask was then cooled under running tap water. The extract was centrifuged for 20 minutes and the solution transferred to a 500-ml. volumetric flask and filled to the mark. Using 25 ml. of this extract the titratable acidity was detrmined by titrating with 0.1 N sodium hydroxide to pH 8.2 as indicated by a Beckman pH meter model G. The remaining extract was brought to pH 7.9 with 0.1 sodium hydroxide and after filling again to the mark 20 ml. aliquots were freeze-dried. The weight of solids was recorded and then the solid extract after acidifying to pH 1 was transferred to the top of a column of silica gel. The organic acids were then separated into 6 bands by a method similar to that reported from this laboratoe (11). The purity of these bands was checked by paper chromatographic methods using the Ri values of Table 2 in the case of phenolic acids. Some of the compounds were identified by physico-chemical methods.The individual fractions from the column were evaporated to dryness. If the presence of volatile acids was suspected, the fractions were neutralized with ammonia before drying. The residues were dissolved in ethanol or ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.