Short Coffee Break

Newspapers and magazines frequently mention how antioxidants 'fight free radicals'. Previously, vegetables and fruits were the most popular foods associated with these antioxidants. Then dark chocolate and coffee joined this group. But have you ever heard of "polyphenol antioxidants"? One Swiss food giant has also jumped on this trend. How? It has started selling a coffee called Green, which claims to contain naturally occurring polyphenol antioxidants that could help protect body cells from daily damage. This coffee contains roasted (green) coffee beans specifically intended to increase antioxidant levels. Coffee is actually one of the richest phenolic sources in Western diets. Sometimes the natural mechanisms that potentially protect body cells cannot keep reactive oxygen species levels under control. Coffee, as a powerful antioxidant source, can address this situation. Yet the story is far more complex than a simple battle between antioxidants and free radicals. Products rich in antioxidants have much lighter modes of action than previously thought, says Alan Crozier, plant biochemist at the University of Glasgow in England. You are accustomed to thinking that coffee is bad for our health. Most people do their best to indulge in this guilty pleasure. However, alongside some magazine articles that have prompted people to question their daily coffee intake and follow their health over the years, numerous epidemiological studies show that regular coffee drinkers have a lower likelihood of developing various cancers, including liver, colon, oral and esophageal cancers. In 2008, a research team from Harvard Medical School in the US and the University of Madrid in Spain evaluated data from two large US epidemiological studies that followed more than 125,000 people over 20 years. They concluded that regular coffee consumption "was not associated with increased mortality rates". In fact, adjusting for risk factors such as weight and specific diseases, the team suggested that people who consumed more coffee had lower cardiovascular disease risk. It has been claimed that coffee helps protect against gout (by lowering uric acid levels), tooth decay and gallstones. There is also strong evidence in particular that coffee provides some protection against type 2 diabetes. When coffee is mentioned, the first chemical compound that comes to mind is caffeine. The beneficial effects of caffeine on the brain are well documented. As for coffee's effects on our palate, is it not relative? Let us briefly mention the abundance of chemical compounds that affect coffee's taste. Coffee contains numerous chemical substances with more than 1,000 aroma compounds. Only a limited number of compounds in this chemical composition have had their structure elucidated. If you are looking for antioxidants, the most abundant phenolic compounds in coffee are chlorogenic acids (CGA), which correspond to 12 percent of the dry weight of green roasted coffee beans. Much of coffee's bitter taste, which sometimes causes reflux (acid reflux) in coffee drinkers, comes from CGAs. CGAs found in coffee are formed by esterification of hydroxyl groups on quinic acid with trans-cinnamic acids (especially caffeic, ferulic and p-coumaric acids). The resulting conjugated CGA structures are known as caffeoylquinic acid, feruloylquinic acid and p-coumaroylquinic acid respectively. Half of the CGAs in green coffee beans undergo some transformation during high-temperature roasting. Some of the CGAs are hydrolyzed to form free phenolic acids or are converted to chlorogenic acid lactones, a bitter sweetener (dehydration). Other CGAs participate in melanoidins, Maillard browning reactions. When toasting bread, we inadvertently cause the formation of the Maillard reaction. These reactions result in brown and very bitter-tasting antioxidant polymers. While CGA concentration in an average tea cup is 20-60 mg, in a brewed cup of coffee it varies between approximately 20-675 mg per cup. CGA levels depend not only on roasting time and temperature but also on the coffee bean itself - Arabica beans have lower CGA levels compared to Robusta and brewing method. According to Yi-Fang Chu, who directs a coffee and health research group in the US, decaffeinated coffee contains similar phenolic levels to caffeinated coffee. In fact, due to the concentration effect that occurs during decaffeination, higher levels of phenolic groups can be found. While writing this review article, I drank more coffee than I have in my life. But with pleasure… To whet your appetite, I have sprinkled a few photographs through the lens of my dear friend Zeynep Özyürek. Now it is time for a break… Make yourself a coffee and enjoy the taste of more than 1,000 aromas… You will only notice one or a few of them… I thank my dear friend Zeynep Özyürek for sharing the photographs with us and our master's student İbrahim Demirci for supporting us with coffee knowledge. Assistant Professor Sultan Funda Ekti Eskişehir Technical University Faculty of Science Department of Chemistry    

References 1. E Lopez-Garcia et al, Ann. Intern. Med., 2008, 148, 904 2. J. Yi et al, Arch. Oral Bio., 2016, 64, 51 3. Y-F Chu et al, Food Chem., 2011, 124, 914 4. Emma Davies, "Chemistry in every cup", https://www.chemistryworld.com. 5. "Why is coffee bitter?- The coffee chemistry", https://www.compoundchem.com