Antibacterial Activity of Roasted Coffee Beans and Caffeine
A Potentially Healthy Beverage
Coffee is the beverage of choice for many people, who love its rich taste and aroma and its stimulating effect. The drink has been linked to a number of important health benefits. A new one may soon be added to the list. Researchers have found that under certain conditions roasted coffee beans and caffeine kill or hinder disease-causing bacteria.
Until quite recently, coffee wasn’t considered to be a health food. Coffee drinking was even considered to be a bad habit due to the drawbacks that some people experience. These include restlessness, inability to sleep, heartburn, stained teeth, and withdrawal symptoms when a person tries to stop drinking coffee. Now researchers are finding that coffee seems to have a variety of health benefits, including reducing the risk of type 2 diabetes, gallstones, liver cancer, Parkinson's disease, and Alzheimer's disease. Antibacterial action might be another great benefit of drinking coffee.
Most research into the antibacterial activities of roasted coffee beans has focused on effects in the mouth and the digestive tract.
Bacteria in the Mouth
Coffee may prevent the adhesion of Streptococcus mutans to teeth. This bacterium is the leading cause of tooth decay and forms a community called a biofilm on the surface of the teeth. The bacteria in a biofilm are surrounded by a protective coating of polysaccharides. Bacterial biofilms form in other places in the body, too. In the mouth, the film is also known as plaque.
The bacteria in the oral biofilm feed on fermentable carbohydrates that enter and remain in the mouth. As they break down the food they produce acid, which softens and destroys tooth enamel. Saliva has a limited ability to prevent the damage by washing the acid away, neutralizing it, and killing bacteria by enzyme action. Once plaque has formed, it must be removed by tooth brushing and dental floss. Once it hardens into tartar (also called calculus), a dental hygienist or dentist has to remove it.
The seeds inside the red coffee berries, or coffee cherries as they are sometimes known, are pale green. They become yellow after being dried in the sun. When they're roasted they turn brown and become the familiar coffee "beans" that we buy in stores.
Coffee and Oral Health
One team of Italian researchers tested different kinds of coffee to see if they could prevent Steptococcus mutans from adhering to simulated teeth. The researchers used hydroxyapatite beads that were coated with saliva in their experiment. Hydroxyapatite is the chief substance in tooth enamel.
The researchers found that both green (raw) and roasted coffee prevented the bacteria from sticking to the teeth, though the roasted product was more effective. Some isolated coffee compounds were also effective. The scientists think that certain chemicals in coffee bind to the tooth enamel, preventing the bacteria from attaching.
Some Brazilian scientists tested green, roasted, caffeinated, and decaffeinated forms of Arabica coffee (Coffea arabica) and Robusta coffee (Coffea canephora), as well as isolated coffee compounds. They found that specific coffee compounds acting together have a bacteriostatic effect on Stretococcus mutans. They didn't kill the bacteria but prevented them from growing and reproducing.
The caffeinated coffees did a better job at hindering bacteria than the decaffeinated coffees and the lighter roasts of coffee did a better job than the darker ones. In addition, the researchers found that the caffeinated Robusta coffee prevented bacterial attachment and biofilm formation.
The discoveries described above are very interesting and could be very important as well. Results in a living body may not be the same as those obtained in lab equipment, however.
Black Coffee Without Milk, Cream, or Sugar
It's probably important that coffee is drunk black, without any additives, if a person hopes to experience any oral health benefits offered by the beverage. Milk and sugar can be harmful to teeth. Sweet or milky coffee drunk slowly is especially dangerous, since the saliva doesn't get a chance to repair any damage to the tooth enamel before it encounters another onslaught of harmful fluid.
Some dentists have noticed an increase in tooth decay in people who spend hours in front of a computer screen, slowly sipping sweetened, milky coffee as they work. Even milky coffee without added table sugar (sucrose) can damage tooth enamel if it's drunk over a long period of time, since milk contains other types of sugars. This is the reason for baby bottle syndrome, also called baby bottle tooth decay, which can occur in babies who suck on a bottle of milk for a long time.
Hydrogen Peroxide Production
In a lab experiment, a group of German scientists found that a suitable concentration of coffee freshly made from roasted coffee beans inhibited the growth of two species of bacteria: Escherichia coli and Listeria innocua. When an enzyme called catalase was added to the coffee, its antibacterial ability was destroyed. The enzyme breaks down hydrogen peroxide. The researchers found that pure hydrogen peroxide (a very dangerous substance for humans) also killed the bacteria, though to a lesser degree than the coffee.
The experiment was done in lab equipment, not living things. This means that the results may not apply to living organisms. They could still be significant, though. They give us more information about the antibacterial action of coffee. It's possible that scientists may eventually be able to make use of the discovery to help humans in some way, even if this benefit occurs outside our body.
Bacteria in the Digestive Tract
Strange as it may sound, the human body is thought to contain around ten times more bacteria than human cells. The bacterial population is often referred to as our microbiome. The bacteria in the microbiome live on our skin and inside internal passageways that connect to the outside world, including the respiratory tract and the digestive tract. The greatest number of bacteria reside in our large intestine.
Researchers are discovering that the bacteria in our large intestine have important effects on our lives, many of them beneficial. Depending on the species, they help to digest food, produce vitamins that we need, fight dangerous microbes, reduce inflammation, and boost immunity. They may also help to lower cholesterol and fight obesity.
Harmful bacteria may be present in our intestine as well as helpful ones, but the effects of the beneficial microbes seem to be dominant under most conditions. Some researchers say that since the intestinal microbiome is so important it should be thought of as an organ in our body.
Coffee and Intestinal Health
A 2019 study at the University of Texas found that coffee (caffeinated or decaffeinated) given to rats for three days decreased the number of bacteria in their feces. The researchers didn't identify whether the decrease was in "bad" bacteria (a group known as enterobacteria), good bacteria (the firmicutes group), or both. The researchers also found that when coffee was added to rat feces placed in a Petri dish, bacterial growth was suppressed.
An earlier study of sixteen people found that moderate coffee consumption (3 cups a day for 3 weeks) had little effect on bacteria in the subjects' large intestines except in reference to one type of bacterium. The coffee actually promoted the activity of Bifobacteria.
Bifobacteria are believed to have beneficial effects on human health. Their role in the intestine isn't known for certain, but they may digest polysaccharides and reduce the numbers of unfriendly bacteria in the gut. Their metabolic activities produce a variety of chemicals, some of which may boost our immune system. Understanding the role of our resident Bifobacteria and their companions is a very important pursuit.
Both of the studies described above have limitations. The first one involved rats instead of humans and didn't identify species of bacteria. The second involved only a small number of people. Nevertheless, the experiments do suggest that coffee may have the ability to affect intestinal bacteria.
Possible Benefits of Moderate Coffee Intake
Researchers have shown that roasted coffee may have many other benefits besides fighting (or perhaps in some cases supporting) bacteria. It's a very interesting beverage
Moderate Coffee Consumption for Health
The consensus of most researchers seems to be that moderate consumption of coffee is fine for someone who enjoys the drink and may provide important health benefits, but excess coffee intake should be avoided. The links between coffee and health are exciting, but some caution is needed when drinking the beverage. As the video above shows, a survey of a large number of people showed that moderate coffee consumption (2 cups a day) reduced the risk of heart disease, whereas heavy consumption (6 or more cups a day) actually increased the risk of heart disease.
Coffee beans contain many different chemicals. There seem to be several compounds responsible for coffee's effects on bacteria. Confusingly, while some researchers say that particular chemicals in the beverage are helpful, others say that these chemicals aren't helpful but that other ones in the drink are. It would be very interesting to know which chemicals are actually useful for controlling specific species of intestinal bacteria.
The identities of the useful chemicals, their effects, and their mechanisms of action need to be clarified. Hopefully researchers will soon learn more about the compounds and discover how to extract them. This may enable people who dislike coffee or who experience unpleasant results when drinking it to benefit from any protective effects that it offers.
- Coffee may help prevent cavities from the EurekAlert news service
- Coffee and Streptococcus adhesion from the NIH (National Institutes of Health)
- Coffee types and antibacterial effects from ScienceDirect
- Effect of coffee on oral bacteria involved in dental caries and periodontal disease (Abstract) from ResearchGate
- Hydrogen peroxide made from coffee from the Royal Society of Chemistry
- Coffee and healthy gut bacteria from the NIH
- Research documents effects of coffee on intestinal bacteria from the ScienceDaily news service
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2012 Linda Crampton