Phenolic acids, a subclass of phenolic compounds, are known for their diverse biological properties, including antioxidant, antiviral, antibacterial, antitumor, neuroprotective and cardioprotective activities. These compounds have garnered significant attention due to their potential applications in various industries, such as food, cosmetics and textiles. This review synthesises recent research on the health benefits of phenolic acids and their industrial applications, emphasising the mechanisms underlying these benefits and the practical uses of these compounds in different sectors.
Phenolic acids are plant-derived secondary metabolites and represent a significant portion of dietary polyphenols. These compounds are prevalent in various fruits, vegetables, grains and other plant-based foods. Their chemical structure, characterised by hydroxyl groups attached to an aromatic ring, grants them the ability to neutralise free radicals, thereby contributing to their antioxidant properties. The increasing interest in natural antioxidants has led to extensive research into the potential health benefits and industrial uses of phenolic acids.
Biosynthesis and bioavailability of phenolic acids
Phenolic acids are biosynthesised in plants through the shikimate and phenylpropanoid pathways. The most common phenolic acids include hydroxybenzoic acid derivatives (for example gallic acid) and hydroxycinnamic acid derivatives (for example caffeic acid). Their bioavailability, however, varies widely depending on their chemical structure, the food matrix and individual metabolic factors.
Upon ingestion, phenolic acids undergo various metabolic processes, including phase I and II metabolism, which alter their bioactivity and bioavailability. The enterohepatic recirculation further affects their concentration in the bloodstream, ultimately influencing their health benefits.
Sources of phenolic acids
Phenolic acids are widely distributed in the plant kingdom. Common sources include fruits and berries, rich sources include apples, cherries and berries, which contain high levels of hydroxycinnamic acids. Furthermore, certain species of algae are emerging as alternative sources of phenolic acids, particularly in regions where terrestrial plant sources are scarce. Often discarded as waste, fruit peels, such as those from citrus fruits, are abundant in phenolic acids and have gained attention for their potential in upcycling processes.
Health benefits of phenolic acids
The health-promoting effects of phenolic acids are well-documented across various studies. Phenolic acids are potent antioxidants that scavenge free radicals, thereby protecting cells from oxidative stress. This property is crucial in the prevention of chronic diseases such as cardiovascular diseases (CVDs) and cancer. Other important effects are their anti-inflammatory properties, by modulating the activity of enzymes like cyclooxygenase (COX) and nitric oxide synthase (iNOS), phenolic acids exhibit significant anti-inflammatory effects, which are beneficial in managing inflammatory disorders. Also, phenolic acids, such as caffeic acid, have shown promise in protecting against neurodegenerative diseases, including Alzheimer's and Parkinson's diseases, by mitigating oxidative stress and inflammation in neural tissues. These compounds also exhibit antimicrobial activities against a broad spectrum of bacteria and viruses, making them potential candidates for developing new antimicrobial agents.
Industrial applications of phenolic acids
The industrial utility of phenolic acids extends to several sectors, with applications that capitalise on their antioxidant, antimicrobial and UV-protective properties. Within the food industry phenolic acids are used as natural preservatives due to their ability to inhibit lipid oxidation and microbial growth, thereby extending the shelf life of food products. For example, caffeoylquinic acid from Moringa oleifera is used to preserve goat meat patties. In the cosmetic industry phenolic acids are incorporated into creams, sprays and other skincare products for their anti-aging, anti-inflammatory and UV-protective effects. Compounds like protocatechuic acid and p-coumaric acid are added to facial creams to enhance skin protection and reduce inflammation. Phenolic acids are also used in the textile industry to improve the UV protection of fabrics. For instance, tannins from oak bark are applied to cotton and silk to increase their UV resistance.
Future perspectives
As the demand for natural and sustainable products grows, phenolic acids are poised to become increasingly important in both health and industry. Future research should focus on optimising extraction methods, improving bioavailability and ensuring the safety and efficacy of these compounds in various applications. Additionally, there is a need for more human studies to better understand the health benefits of phenolic acids and to translate these findings into practical recommendations.
In conclusion, phenolic acids are versatile compounds with significant potential for both health and industrial applications. Their antioxidant, anti-inflammatory and antimicrobial properties make them valuable in preventing and managing chronic diseases, as well as in developing natural preservatives and protective agents in food, cosmetics and textiles. Continued research and development in this area will likely lead to the expanded use of phenolic acids in various industries, contributing to healthier products and sustainable practices.