Phenolic acids

Phenolic acids are a group of secondary plant substances that belong to the polyphenol family. They are found in a variety of foods and play an important role in human nutrition and plant physiology. These compounds are known for their antioxidant, antimicrobial and anti-inflammatory properties. Phenolic acids have the potential to provide various health benefits. In this article, the structure, occurrence, health effects and importance of phenolic acids are discussed in detail.

Chemical structure and classification

Phenolic acids are aromatic carboxylic acids whose basic structure is phenol, to which a C1 carbon group is attached. They can be divided into two main categories:

1. Hydroxybenzoic acids: These include compounds such as gallic acid and vanillic acid.
2. Hydroxycinnamic acids: This group includes caffeic acid, ferulic acid and other related compounds.

The structure of phenolic acids enables them to act as antioxidants by neutralising free radicals and thus preventing cell damage.

Occurrence in food

Phenolic acids are abundant in many plant foods. The most important sources include

• Coffee and tea: these drinks are particularly rich in chlorogenic acid, a hydroxycinnamic acid known for its antioxidant properties.
• Fruit and vegetables: Apples, berries, cherries, grapes, carrots and tomatoes contain significant amounts of phenolic acids.
• Wholemeal products: Grains such as barley and oats are also rich in these compounds.
• Nuts and pulses: These foods also contribute to the intake of phenolic acids.

Health effects of phenolic acids

The health benefits of phenolic acids are varied and well documented. The most important effects include

1. Antioxidant properties

Phenolic acids act as powerful antioxidants that can neutralise free radicals and reduce oxidative stress. Oxidative stress is a known risk factor for many chronic diseases, including cardiovascular disease and cancer.

2. Antimicrobial effect

Some phenolic acids exhibit antimicrobial properties that can inhibit the growth of bacteria and fungi. This effect is particularly relevant in the food industry, where phenolic acids are used as natural preservatives.

3. Anti-inflammatory effects

Studies have shown that phenolic acids have anti-inflammatory properties. They can inhibit the production of pro-inflammatory cytokines and thus reduce chronic inflammation in the body.

4. Cancer prevention

Some research suggests that phenolic acids can potentially reduce the risk of certain types of cancer. They work by inhibiting the activity of phase I enzymes that activate carcinogenic compounds and promoting the activity of phase II enzymes involved in the detoxification of carcinogens. In an animal study from 2018 , the phenolic acid ellagic acid inhibited the growth of breast cancer tumours in mice. Treatment with ellagic acid reduced tumour size and progression and increased the survival rate of the animals. The authors conclude that ellagic acid could be a promising molecule for the prevention and treatment of breast cancer.

5. Cardiovascular health

Eating foods rich in phenolic acids is said to help improve cardiovascular health. Phenolic acids can lower blood pressure, potentially improve blood lipid levels and promote endothelial function, which reduces the risk of heart disease. A meta-analysis from 2016 evaluated 10 studies with a total of 283,884 participants. The researchers found an inverse relationship between the consumption of phenolic acid-rich foods and the risk of cardiovascular disease. Each 100 mg increase in phenolic acid intake per day was associated with a 6% lower risk of cardiovascular events.

Bioavailability and metabolism

The bioavailability of phenolic acids varies depending on the type of compound and the source. After ingestion, they are absorbed in the small intestine and metabolised in the large intestine by the intestinal microflora. Some studies show that the bioavailability of hydroxycinnamic acids is higher than that of hydroxybenzoic acids.

Bioavailability refers to the proportion of an active ingredient that enters the bloodstream unchanged and is therefore available at the site of action. It is an important pharmacological parameter that indicates how quickly and to what extent a substance (often a drug) is absorbed and takes effect.

Bioavailability can be measured in various ways:

• Absolute bioavailability: this indicates how much of the active substance is available in the blood after non-intravenous administration compared to intravenous administration.
• Relative bioavailability: This compares the bioavailability of an active substance in a specific dosage form with another dosage form that is regarded as standard.
• Oral bioavailability: This refers specifically to the bioavailability after oral administration.