Coffee flavor studies

The first member of this class identified in a coffee flavor, and even in food, was 5-acetyl-2-methylox-azole (L.23) found by Stoffelsma and Pypker (1968) and Stoffelsma et al. (1968) but without mention of a reference compound. An intensive study on the presence of oxazoles in coffee aroma was conducted somewhat later by Vitzthum and Werkhoff (1974a,b). A coffee extract was obtained by steam distillation, enriched by adsorption/desorption and extracted with dilute hydrochloric acid. The compounds in this basic fraction were identified by classical GC/MS combination, among them 20 oxazoles in concentrations of the order of 1-10 ppb. The reference standards were prepared or purchased and their NMR spectra were measured. 

In other flavor perception studies, the PTR mass spectra of the headspace of seven different brands of mozzarella cheese held at 36 C have been first compared with the judge panel flavor profile [157]. A PCA of the mass spectral data was used to discriminate different cheese types. And a trained panel of sensory judge was employed to give qualitative and quantitative analysis of mozzarella cheese. It was found that there was an interesting and clear similarity between the classical sensory and the instrumental analysis. More recently, a robust and reproducible model was developed to predict the sensory profile of espresso coffee, and the model was derived from 11 different espresso coffees, which had been analyzed by a trained panel and PTR-MS, and further validated using eight additional espressos [158]. Flavor studies of whey [159], custard desserts [160], other types of cheeses [148,161], milk [162], wine [163,164], apples [165],olive oils [166],bread [167], and butter and butter oil [168,169] were also conducted by the PTR-MS system. 

In terms of key aroma components, Czerny et al. [59] conducted sensory studies using volatiles identified in previous studies as potential contributors to coffee aroma [60] to determine the odorants truly characterizing freshly brewed Colombian coffee. They found 2-furfurylthiol, 4-vinylguaiacol, several alkyl pyrazines, furanones, acetaldehyde, propanal, methylpropanal, and 2- and 3-methylbutanal had the greatest impact on the coffee flavor. 

Additionally, Villanueva et al. studied die eo-extraction of other valuable eom-pounds of coffee, such as phenolic compounds (mainly chlorogenic acids) and oils. These substances have an important role during coffee roasting as preeursors of key eompounds of coffee flavor and aroma and thus, their removal from natural matter during extraction should be minimized. 

Field spray studies have been carried on using benzene hexachloride and similar insecticides. In Brazil benzene hexachloride appeared to have a toxic effect on coffee trees. It has been the source of a bad flavor in coffee in Africa and also in Brazil, which was a further reason for abandoning its use. Work with so-called deodorized benzene hexachloride compounds and other insecticides is now in progress. 

Practical experience abetted by statistical surveys reveals a wide diversity of taste and odor preferences among peoples worldwide. For example, in studying preferences for flavored yogurt, strawberry is the clear winner in a majority of countries surveyed. Exceptions were a preference for cheny (Germany), citrus (Japan), coffee (Swiizerland). and blueberry (Austria). The least preferred flavors were orange, tropical, peach, and banana flavors. 

T. Hofmann, M. Czerny, S. Calligaris, and P. Schieberle, Model studies on the influence of coffee melanoidins on flavor volatiles of coffee beverages, J. Agric. Food Chem., 2001, 49, 2382-2386. 

In 1916 he began to study chemistry at the E.T.H. at Zurich and graduated in 1920. In 1922 he began a nine-year research project on the composition of the flavoring substances in roasted coffee. 

One challenge cing the flavor industry today deals witii the stability of process/reaction flavors to heat, UV-light, oxidation, binding to food mafrices, diffusion and interactions with the enviroiunent in v ch they find application. Seeventer et al. (75) studied the stability of thiols formed from model system ribose/cystein, and reported that 2-methyl-3-furandiiol, 2-furfiirylthiol, 2-mercapto-3-butanone and furaneol decreased during storage. In brewed coffee. 

Phenolic acids of dietary origin result essentially from such products as tea, cofFee, fruits, vegetables, and flavored beverages (NIO). Those acids which are end products of endogenous metabolism are, of course, particularly interesting the study of their pathological modifications can help to detect a number of diseases. 

The traditional equilibrium method of flavor release study mentioned above is extremely time consuming, and several weeks are commonly needed to obtain full release profiles of flavors from powders. Recently, thanks to the pioneering work of Dronen and Reineccius (2003), proton transfer reaction mass spectrometry (PTR-MS) has been used as a rapid analysis to measure the release time-courses of flavors from spray-dried powders. The PTR-MS method has been applied extensively to analyze the release kinetics of volatile organic compounds from roasted and ground coffee beans. The release profiles could then be mathematically analyzed by means of Equation 1.1 to obtain the release kinetic parameters, A and n (Mateus et al., 2007). 

Water had a relatively weak effect on the sensor array. This is helpful if we are trying to detect substances that are much more reactive than water. In fact, it might be possible to configure the sensor array to study flavor notes in aqueous substances such as coffee or tea. If, on the other hand, humidity measurement is desired, then the presence of more volatile constituents in the system may mask any response to humidity. 

Smith (1963a) and Feldman et al. (1969) underlined the importance of non-volatile compounds to the flavor of coffee. The comparison between the composition of green and of roasted coffee showed an important decrease in the content of proteins, chlorogenic acid and sucrose on roasting. Fractionation and analysis of the aroma precursors in green coffee have also been studied by Russwurm (1970) who considers that the non-volatile constituents of green coffee that may be involved in flavor formation are carbohydrates, proteins, peptides and free amino acids, polyamines and tryptamines, lipids, phenolic acids, trigonelline and various non-volatile acids. 

Bade-Wegner et al. (1998) studied the volatile compounds associated with the over-fermented flavor defect, considered to be one of the most objectionable organoleptic defects in coffee. They examined two defective samples of arabica and one sample of robusta green coffees, comparing them to reference products with a neutral flavor. As the off-flavor can be due to overfermentation of green coffee or to the presence of so-called stinker beans, the authors considered that the previous studies and identifications were more indicative than causative. By GC-olfactometry, three fruity odor notes were perceived, at different intensities, that were attributed to ethyl 2-methylbutanoate (Section 5,F.40), ethyl 3-methyl-butanoate (Section 5,F.41) and ethyl cyclohexanecarboxylate (Section 5,F.46). The three esters were considered to be the most important contributors to the over-fermented flavor defect. 

Schlich et al. (1987) proposed a new approach to selecting variables in principal component analysis (PCA) and getting correlations between sensory and instrumental data. Among other studies, Wada et al. (1987a,b) evaluated 39 trade varieties of coffee by coupling gas chromatographic data with two kinds of multivariate analysis. The objective classification was compared with the sensory data (cup test), directly or after statistical treatment. The results were concordant. Murota (1993) used qualitative sensory data to interpret further the results of GC data and canonical discriminant analysis. He could thus suggest which were the components responsible for the flavor characteristics in different coffee cultivars. 

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