Phenolic acids are a group of phytochemicals part of the wider polyphenol family. There are thousands of other polyphenols, the best known types being include flavonoids and stilbenes. Phenolic acids are very common in nature and can be found in most plants. The best sources for them are vegetable leaves and the seeds and skins of fruits.
A normal diet should provide a good amount of phenolic acids. If you consume whole cereals, fruits and vegetables, you will get all the phenolic acids needed by your body. Many foods are a rich source for these nutrients, for example whole cereal flour made from wheat, corn, oats and rice, red wine, tea, coffee and fruits like plums, cherries, kiwis, onions, mangos, berries, apples or citrus fruits.
Nature provides many varieties of phenolic acids, which are divided into the more common cinnamic acids and the rarer benzoic acids. Gallic acid is the best known of the benzoic acid derivatives, while the derivatives of cinnamic acid include caffeic acid, ferulic acid and many other similar compounds.
Black tea and grape seeds are very rich in gallic acid. Another very good source of phenolic acids is coffee, which supplies good amounts of caffeic acid and chlorogenic acid. Caffeic acid is also abundant in fruits like forest berries, apples, kiwis, plums and cherries. The husk of cereals, which is available as whole grains, provides ferulic acid. The best source for ferulic acid is whole corn flour, followed by flour made from whole wheat, rice or oats.
It has been known for a long time that foods rich in phenolic acids provide important health benefits. However, since these foods supply many other important nutrients, such as bioactive compounds and fibers, it isn't known if these benefits can be credited to phenolic acids or not. Most vegetables and fruits are very rich in fibers and other natural nutrients, as well as a separate category of polyphenols known as flavonoids.
While drinking coffee is often considered to be a vice, it is also linked with a lower risk of chronic diseases and cancer. This might be due to its content of caffeic acid and chlorogenic acid, but coffee is also rich in caffeine and other potentially beneficial substances. Red wine is rich in phenolic acids but also resveratrol, a compound that might have strong effects on human health.
Some dietary supplements with phenolic acids are available in specialized stores. These are often rich in gallic acid, since they are prepared from extracts of green tea or grape seeds. They are sold under the larger group of antioxidant supplements. However, modern nutritionists have established that consuming raw fruits and vegetables offers more antioxidants than commercial supplements.
Plants synthetize a number of bioactive compounds as secondary metabolites, including all types of phenolic compounds like flavonoids and phenolic acids. Their role is to pass signals between plants and various micro organisms. Since plants live in a symbiotic relationship with many useful microbes, this is a critical function that initiates and maintains the partnership.
Phenolic compounds can transmit various signals in this relationship. Legumes for example produce flavonoids that activate the secretion of nod factors by Rhizobia, a bacterium that can fix nitrogen. These nod factors also serve as signalling molecules, on the plant's roots. The leguminous plant is capable of recognizing these molecules and it reacts to their presence. This is the start of the symbiotic relations between the plant and bacteria, which benefits both of them.
Plants might also produce phenolic compounds as a defensive mechanism, in order to fight against various pathogens that can start diseases. Other phenolic chemicals have different roles. For example, salicylic acid is very important for photosynthesis and the development of the plant. Other phenolic acids are needed for the plan's reproduction cycle. Flavonoids are the compounds that give flowers their vivid color, which attracts insects that pollinate them.
Phenolic acids are digested very quickly, since they are absorbed straight through the intestinal tract. While their actual effects are not well understood, these phytonutrients are considered to be antioxidants that prevent the damage caused by free radicals. At the same time, they also have anti-inflammatory properties. Several major types of phenolic acids exist.
Ellagic acid is an effective anti-oxidant that reduces overall oxidative pressure. Studies have also revealed that it can protect human DNA from several major carcinogens. It is found in some nuts and fruits, especially raspberries, strawberries, walnuts, wolf berries, grapes, peaches, blackberries, cranberries, pecans or pomegranates.
Hot chilli peppers provide good amounts of a phenolic acid named capsaicin. It has a direct action when applied on the skin, treating diseases such as psoriasis and reducing pain. It can cure some types of headache when included as an ingredient in nasal sprays. When ingested, it causes a feeling of happiness by stimulating the production of endorphins. It also limits the expansion of prostate tumours and shields the stomach against ulcers.
Tannic acid is one of the best known phenolic acids. It has a strong action against toxins, pathogens, oxidants and mutagenic agents, so it is considered a possible preventive treatment for diabetes, cancer or Alzheimer's disease. It can also stop diarrhea due to its astringent effects. It if found in many foods, for example green tea, lemons, limes, melons, oranges, peas, pineapples, spinach, wine, apricots, asparagus, blackberries, broccoli, cabbage, chocolate, grapefruits and grapes.
THC, or Tetrahydrocannabinol, is a famous component of the marijuana plant, found in the highest concentration in the resin glands that cover female flower buds. It provides the well-known recreational drug effects of cannabis, providing relaxation as well as anti-emetic and appetite enhancing properties. It is also an effective natural analgesic and other effects on health include anti-inflammatory action, seizure control and the reduction of intraocular pressure. It has a strong action against cancer, inhibiting the expansion of lung cancers and brain tumors (glioblastoma).
Herbs usually supply a type of phenolic acids known as monophenols. They are also effective antioxidants that can scavenge and destroy harmful free radicals. Just like the other similar compounds, monophenols are considered a potential weapon against cancer.
Phenolic acids are known for their quick absorption and might provide useful health benefits. These are mainly due to their antioxidant effect, which stops free radicals from damaging or mutating cells. These compounds also have anti-inflammatory properties, but only when a constant amount is ingested.
Scientists have investigated phenolic chemicals for their potential use in the medical, biological and even agricultural fields. Most of these studies have revealed the already known effect of these compounds as strong antioxidants. Since free radicals are considered to be the root cause of many serious conditions, phenolic acids might be very important for health.
Free radicals are a normal product of the human metabolism and the body has some mechanisms to defend against them. However, if their level is allowed to increase unchecked, free radicals can react with cells and damage them, triggering lethal diseases like heart attacks or cancer.
The anti-inflammatory properties of phenolic acids are less powerful, but some of them can provide useful relief to people suffering from arthritis and other inflammatory conditions. A type of hydroxybenzoic acid, known as gallic acid, can reduce the intensity of inflammatory and allergic reactions by inhibiting histamines, cytokines and other chemicals that trigger them. This effect can prevent the worst symptoms associated with inflammation.
Phenolic acids and some other compounds from the larger phenolic family also have antiseptic effects. Defence against pathogens is actually one of the reasons why plants synthetize phenolic acids. They might provide the same benefits when ingested as part of a normal human diet. The same gallic acid can kill viruses and fungi, while cichoric acid was also found to be an effective antiviral agent.
Phenolic acids are also known for their use in cosmetics, and some of them are included as ingredients in various products: rosmarinic acid, caffeic acid, gallic acid or ellagic acid. Salicylic acid, 4-Hydroxybenzoic acid and other phenolic acids are used in both medicine and industry. Paraben, one of the most common chemical preservatives found in cosmetics, is produced from 4-Hydroxybenzoic acid. Salicylic acid can reduce skin problems like acne, warts, dandruff or psoriasis and is included in many products for this purpose. Phenolic acids might also be a good natural alternative to replace BHT (Butylated hydroxytoluene) and BHA (Butylated hydroxyanisole), which are the main synthetic antioxidants added to food.