Coffee chemistry in your cup
Coffee has a diverge repute - is it a guilty pleasure or a lifesaving brew? We gulp down an shot of espresso and investigate.
It’s hard to miss snippet stories about the latest favorite food to join the anticancer team. Initially it was select greens and fruits, then niche wine, cocoa, chocolates and now Coffee. We frequently read and hear that coffee poly-phenol oxidants combat the cells from day to day damage.
Coffee is one of the richest sources of carbolic acid, phenolics in the modern diet and packs a strong antioxidant boost. Breaking down this sentence means that it protects the body’s organic mechanism fail to keep levels of active oxygen under control. Yet, the fact is more complex than a simple battle between antioxidants and phenolics. Antioxidant-rich products, from coffee to wine (red) has far subtle modes of work than previously thought, says Dr,Manjunath GS, a neurosurgeon at Apollo Hospital, Mysore.
Coffee is a powerhouse of chemicals, with over 1000 aroma compounds. The most abundant phenolic compounds in coffee are chlorogenic acids (CGS’s), which account for up to 12% of the dry weight of green un-roasted coffee beans. . Much of coffee’s bitter taste comes from CGAs, which also cause the acid re flux that is sometimes experienced by coffee drinkers.
CGAs form in the coffee plant by esterification of trans-cinnamic acids (mainly caffeic, ferulic and p-coumaric acids) with hydroxyl groups on quinic acid. The resulting conjugated CGA structures are known as caffeoylquinic acids, feruloylquinic acids and p-coumaroylquinic acids respectively.
Up to half of the CGAs in green coffee beans degrade during high-temperature roasting, which causes a host of chemical reactions. Some of the CGAs hydrolyze to form free phenolic acids or dehydrate to bitter-tasting chlorogenic acid lactones. Others are involved in Maillard browning reactions to give a wide range of compounds including brown colored and very bitter-tasting antioxidant polymers called melanoidins.
The concentration of CGAs in a cup of brewed coffee varies hugely, from about 20-675mg per cup - compared with 20-60mg in an average cup of tea. CGA levels not only depend on roasting time and temperature, but also on the coffee beans - Arabica beans have lower levels of CGAs than Robusta - and the brewing method. Decaffeinated coffee contains similar levels of phenolics to caffeinated coffee, and can contain higher levels, thanks to a concentration effect that occurs during decaffeination.
Carcinogens in coffee
Of course, there are negatives. For example, coffee contains 4-methylimidazole, which the US National Toxicology Program (NTP) has identified as a carcinogen. The compound is used to manufacture many products, from dyes to agricultural chemicals and rubber. But it can also form through the Maillard reaction in foods and drinks, particularly those with a caramel flavor such as Cola.7 The levels of 4-methylimidazole in cola drinks are similar to those in coffees.
Caffeine in the bloodstream
Caffeine is known to improve memory and the speed with which our brains process information. It binds to some of the same receptors as adenosine, a compound that promotes sleep, amongst other things. Caffeine is a non-selective antagonist at A1 and A2A adenosine receptors in the heart and the brain, having an opposite effect to adenosine and producing a stimulant effect.
There is also a suggestion that caffeine can perhaps benefit those suffering from Alzheimer’s disease. The theory is that blocking the A2A receptors weakens the damage caused by beta-amyloid, the peptide that accumulates in the brain with Alzheimer’s. Giving caffeine to mice engineered to have the disease limited their levels of beta-amyloid and increased adenosine levels.4 Human studies have not brought out strong links between caffeine and Alzheimer’s although analysis of Finnish data on 1409 people over 21 years led at the University of Kuopio, Finland, suggested that people who drank 3-5 cups of coffee per day had a greatly reduced risk of developing Alzheimer’s or dementia.
CGAs in coffee are absorbed in the small intestine to appear in the circulatory system mainly as glucuronidated (coupled with glucuronic acid, a common way the liver solubilises compounds to prepare them for excretion via the kidneys), sulfated and methylated metabolites, explains Crozier. ’It seems as if the compounds trigger events and depart. The body gets rid of them pretty quickly.
It is also becoming clear that the large intestine (colon) plays a crucial role in getting GCAs and their metabolites into the bloodstream. Crozier’s team has collected evidence for this by analysing ileal (small intestine) fluid samples from people who have had their colons removed (ileostomists). In such people, only 30 per cent of CGAs were absorbed in the small intestine, suggesting that 70 per cent would have passed to the colon in healthy people. 2
Crozier’s team used liquid chromatography-mass spectrometry (LC-MS) to analyse urine samples from the ileostomists and from people with healthy colons. The ileostomists excreted only 8 per cent of their intake of CGAs in urine while healthy volunteers excreted 30 per cent. The CGA compounds absorbed in the colon ’must have been in the circulatory system in relatively high concentrations compared to the compounds that are absorbed in the small intestine.
Crozier’s coffee work whose chemists synthesised CGA metabolites to help understand the reaction and degradation pathways in the body. The theory is that quinic acid cleaves from the CGA in the small intestine to release caffeic and ferulic acids, which go on to form glucuronides and are also metabolised to sulfates. We know from analysing the ileal fluid that a mixture of the parent compounds and some of the metabolites pass from the small to the large intestine,’ explains Crozier. ’In the colon, some are absorbed as parent compounds, together with sulfates and glucuronides, but most are chopped up by colonic bacteria to form simple phenolic acids.
The ferulic and caffeic acids form phenolic acids such as dihydroferulic acid or dihydrocaffeic acid. People are starting to get interested in the impact of these things on colonic health. There are some suggestions that the compounds could act as prebiotics, stimulating the gut bacteria.
There is growing evidence that compounds broken down in the colon form a key part of the bioavailability equation of flavonoids and related compounds that not only occur in coffee, but also in vegetables and other beverages, says Crozier. What is more, the colon-derived phenolic acids appear to have in vitro anti-inflammatory activity, and to protect human nerve cells against oxidative damage, says Crozier. Some of the phenolic acids are also thought to be involved in helping to prevent regular coffee drinkers from developing type 2 diabetes.
Swings and roundabouts
So many chemicals to think about. If you already enjoy drinking coffee, it is nice to think that you might be doing yourself some good. Do you take milk? Or sugar? If so, you may be changing the antioxidant chemistry. Crozier has already shown that adding cream to strawberries slows absorption of antioxidants and studying the effects of additives on the bioavailability of coffee’s antioxidants is next on the agenda for many coffee chemists.
Whatever the science may be, coffee certainly gets the brain into gear in the morning and gives much pleasure. Just remember the key word that is never far from a nutritionist’s lips when it comes to red wine and coffee.