Phenols in Coffee

Ye et al. have determined catechin, rutin, ferulic acid, o-dihydroxybenzene, chlorogenic acid, caffeic acid, gallic acid, and protocatechuic acid in coffee by CE-AD [24]. The working electrode was a carbon disk electrode at an applied potential of -1-0.95 V (vs. SCE). Under the optimum conditions, the analytes can be well separated within 26 min in a 75-cm-long fused-silica capillary. The current response was linear over three orders of magnitude with detection limits ranging from 60 to 360ng/ml for all analytes. 

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Ramirez-Coronel, M.A. et al.. Characterization and estimation of proanthocyanidins and other phenolics in coffee pulp (Coffea arabica) by thiolysis-high-performance liquid chromatography, J. Agric. Food Chem., 52, 1344, 2004. 

Heinrich L. and Baltes W. (1987a) Determination of phenols in coffee. Z. Lebensm. Unters. Forsch. 185, 362-5. 

A high proportion of the aromatic compounds in coffee beans are phenolic and presumably they are derived from the lignin and tannin of the cell structure.2 Hydroquinone is present in coffee beverages, 0.3 ppm, either in the free form or as its p-D-glucopyranoside, arbutin.35... 

Some phenolic compounds found in coffee beans.3 TABLE 5... 

Crossing the boundaries of phenolic compounds and amino acids in coffee, caffeoyl tryptophan, and p-coumaiyl-(L)-tryptophan have both been identified recently in green Robusta coffee beans.51 A... 

The chemical origin of free radicals in coffee is attributed to the sugars or carbohydrates, rather than phenolic constituents100. 

Most alkaloids exist in nature not in their free-base form but rather as the salt of naturally occurring acids known as tannins, a group of phenol-based organic acids that have complex structures. The alkaloid salts of these acids are usually much more soluble in hot water than in cold water. The caffeine in coffee and tea exists in the form of the tannin salt, which is why coffee and tea are more effectively brewed in hot water. As Figure 12.19 relates, tannins are also responsible for the stains caused by these beverages. 

Wine, of course, is not the only food that contains phenolics. Phenolics are found in all foods, though at low levels in most. Notable foods that are high in phenolics include coffee and tea, chocolate, fruits and derived products, some oils, spices, and some whole grains. Although the following methods were developed for—and first applied to—analysis of wines and grapes, they can be adapted for other foodstuffs (also see Commentary). 

JR Ramirez-Martinez. Phenolic compounds in coffee pulp Quantitative determination by HPLC. J Sci Food Agric 43 135-144, 1988. 

Figure 1 Content (g/kg) of 5-caffeoyl- and 5-feruloyl-guinic acids in coffee Arabica and Robusta and their corresponding phenols (ppm) formed during roasting...

Woodman et al. (1968) developed a gravimetric method (by means of the sodium salts) for determining the total carboxylic acids present in infusions of Santos coffee. This quantity increased with the degree of roasting, a consequence of the destruction of phenolic acids. From the 12 identified acids, eight were said to be reported for the first time in coffee 2-furoic acid (1.103) (see Section 5.1), mesaconic acid (E.50), fumaric acid (E.47), citraconic acid (E.51), itaconic acid (E.52), lactic acid (E.30), succinic acid (E.44) and maleic acid (E.48). In fact, fumaric, lactic and succinic acids were mentioned by Schormtiller et al. (1961) (see above). 

Later, Tressl et al. (1976) also proceeded to the thermic degradation (2 h, 200 JC) of ferulic acid (H.87) and identified the same phenols as Fiddler et al., plus 4-isopropylguaiacol and vanillin alcohol (4-hydroxy-3-methoxybenzenemethanol) which have not been found in coffee. For isoeugenol (H.38), the formula is written as the (E)-( trans -) isomer, but nothing was specified in the text. Tressl et al. (1976) also published the results of thermal decomposition of cinnamic, p-coumaric (H.84) and sinapic (H.90) acids. Many of the simple phenols (and other aromatic compounds) formed have also been identified in roasted coffee volatiles. A thermic fragmentation of quinic acid (E.62) has shown that simple acids, phenols and polyphenols originate from this precursor (Tressl et al., 1978a). 

Fig. 5.8 Progressive identification of phenols in roasted coffee volatiles...

According to Winter et al. (1976e), at a concentration of 5 ppm in a syrup base, it has a phenolic, ground-coffee taste, becoming groundsy, cereal-like and enhancing the roasted note when tasted in a neutral, soluble coffee base. The threshold value is of 1 ppm in a bland edible oil (Evans et al., 1971). 

Identification and quantitation of phenols in cigarette MSS To date, the number of phenols identified in tobacco smoke exceeds 400 (see Table IX.A-22). While the number of phenols identified is significantly fewer than the number of PAHs identified in cigarette MSS, the number of identified tobacco smoke phenols is much greater than that identified in any other consumer product such as tea, coffee, or cocoa, again a reflection of the intense scrutiny directed at tobacco smoke vs. that directed at any other consumer product. 

First systematic studies aimed at characterizing the precursors of these radicals in green coffee beans evidenced that the radical in coffee is most likely generated upon thermal reactions involving carbohydrates, and excluded phenols as natural source for these radicals (14). 

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