Cytotoxicity of coffee in human intestinal cells in vitro and its inhibition by peroxidase

On-line HPLC analysis of the antioxidant activity of phenolic compounds in brewed, paper-filtered coffee

Caffeoyl-, feruloyl- and dicaffeoylquinic acids (chlorogenic acids) in infusions from green and medium roasted coffee beans were identified and quantified by reverse phase HPLC with photodiode array and MS³ detection prior to assessment of the antioxidant activity using an HPLC system with post-column on-line antioxidant detection based on 2,2'-azinobis-3-ethylbenzothiazoline-6-sulphonic acid radical scavenging activity. Caffeoylquinic acids were the most abundant antioxidants and roasting induced isomerisation with a decline in 5-O-caffeoylquinic acid and concomitant increases in the 3- and 4-O-derivatives. This did not affect the level of caffeoylquinic acid-derived antioxidant activity in the roasted coffee. Roasting did, however, result in the appearance of additional unidentified HPLC peaks with antioxidant activity. Because of this and an increase in the antioxidant activity of components that did not elute from the reversed phase HPLC column, the antioxidant capacity of the beverage derived from medium roast beans was double that of the unroasted coffee. The antioxidant activity of coffees that have undergone different degrees of roasting would, therefore, appear to be due to combinations of different components. The effect of roasting on chlorogenic acids in coffee beans is considered, and the possible contribution of Maillard reaction products to the antioxidant capacity of roasted coffees is discussed.

The inhibitory effects of coffee on radical-mediated oxidation and mutagenicity

Hydrogen peroxide (H2O2) has been implicated as a major contributor to coffee mutagenicity and genotoxicity in vitro. We have used three assays to show the gradual formation of H2O2 in freshly prepared roasted ground coffee and in instant coffees over time reaching levels of 400-450 microM after a 1-h incubation period. Formation of H2O2 occurs through an auto-oxidation process where polyphenolics, in the presence of transition metals, reduce atmospheric oxygen. However, because of these polyphenolics, coffee also possesses in vitro antioxidant activity as shown by its capacity to inhibit lipid peroxidation in Fenton-catalysed hydroxylation reactions. The pro- and antioxidative effects of coffee are also reflected in its mutagenic and antimutagenic activity in the Ames test. Coffee is directly mutagenic in strains TA100 and TA102 due to H2O2 formation. However, coffee is also an antioxidant and antimutagen. This beverage exerts a strong protective effect against the mutagenicity and cytotoxicity induced by the oxidant t-butylhydroperoxide (t-BOOH). Thus, coffee, like many antioxidants, exhibits dual effects in vitro which are highly dependent upon parameters such as dose, atmospheric oxygen, transition metals as well as the biological and chemical endpoints used for measurement. Consequently, the data obtained on the pro- and antioxidant properties of foods and beverages from in vitro bioassays must be interpreted with caution and the results are not easily extrapolated in vivo to assess the impact on human health.

Potential genotoxic, mutagenic and antimutagenic effects of coffee: a review

Coffee and caffeine are mutagenic to bacteria and fungi, and in high concentrations they are also mutagenic to mammalian cells in culture. However, the mutagenic effects of coffee disappear when bacteria or mammalian cells are cultured in the presence of liver extracts which contain detoxifying enzymes. In vivo, coffee and caffeine are devoid of mutagenic effects. Coffee and caffeine are able to interact with many other mutagens and their effects are synergistic with X-rays, ultraviolet light and some chemical agents. Caffeine seems to potentiate rather than to induce chromosomal aberrations and also to transform sublethal damage of mutagenic agents into lethal damage. Conversely, coffee and caffeine are also able to inhibit the mutagenic effects of numerous chemicals. These antimutagenic effects depend on the time of administration of coffee as compared to the acting time of the mutagenic agent. In that case, caffeine seems to be able to restore the normal cycle of mitosis and phosphorylation in irradiated cells. Finally, the potential genotoxic and mutagenic effects of the most important constituents of coffee are reviewed. Mutagenicity of caffeine is mainly attributed to chemically reactive components such as aliphatic dicarbonyls. The latter compounds, formed during the roasting process, are mutagenic to bacteria but less to mammalian cells. Hydrogen peroxide is not very active but seems to considerably enhance mutagenic properties of methylglyoxal. Phenolic compounds are not mutagenic but rather anticarcinogenic. Benzopyrene and mutagens formed during pyrolysis are not mutagenic whereas roasting of coffee beans at high temperature generates mutagenic heterocyclic amines. In conclusion, the mutagenic potential of coffee and caffeine has been demonstrated in lower organisms, but usually at doses several orders of magnitude greater than the estimated lethal dose for caffeine in humans. Therefore, the chances of coffee and caffeine consumption in moderate to normal amounts to induce mutagenic effects in humans are almost nonexistent.