Flavonoids and Phenolic Acids as Potential Natural Antioxidants

Biljana Kaurinovic and Djendji Vastag

## Abstract

For centuries, aromatic herbs and spices have been added to different foods to improve the flavor and organoleptic properties. The use of aromatic plants and spices in phytotherapy is mostly related to different activities of their essential oils, such as antimicrobial, spasmolytic, carminative, hepatoprotective, antiviral, and anticarcinogenic activities. Furthermore, many studies point to strong antioxidant activities of aromatic plants and their essential oils. Knowing that phenolic compounds are the most responsible for the antioxidant activity, the amount of total phenolic contents and content of flavonoids have also been determined. In order to examine the antioxidant properties of five different extracts of Laurus nobilis L. leaves, various assays which measure free radical scavenging ability were carried out: 1,1-diphenyl-2-picrylhydrazyl, hydroxyl, superoxide anion, nitric oxide and hydroxyl radical scavenger capacity test, and lipid peroxidation assay. In all of the tests, only the EtOAc extract showed a potent antioxidant effect.

Keywords: aromatic plants, flavonoids, phenolic acids, ROS, oxidative stress

## 1. Introduction

The history of medicinal herb usage dates back to the distant past, many centuries and civilizations ago. Plants have played an important role in many cultures in the treatment of various diseases, and floral fragrances have been used to refine the spirit and body, to attract partners, and to establish a psychophysical balance. The first written testimonials on the use of herbs for treatment are found in China. Emperor Kin-Nong knew about 100 medicinal plants in 3000 years BC. One of the oldest classical medical texts of ancient China is "Pent-Sao," which was written 2500 years BC and is composed of 52 books; of which, two books are dedicated to herbal remedies. In the nineteenth century, medicinal and exotic plants have become lucrative, as more and more people began growing plants in their homes. China, Japan, and South America were overwhelmed by collectors from plant companies who looked for tropical plants to meet the needs of society. This instigated scientific pharmacy and the start of chemical and physiological research on medicinal herbs. It can be said that the nineteenth century was the century of alkaloids, because hundreds were isolated from plants from all over the world. The beginning of the twentieth century threatened medicinal herbs to be completely thrown out of use. Thus, "medicines" that have been successfully used for thousands of years have become subject to mockery and disdain. The expulsion of medicinal herbs from therapy can be compared to the darkness of the Middle Ages that had ruled Europe.

#### Antioxidants

In the last four decades, especially in the developed countries of Europe and America, scientists have shown increasing interest in plant research. It is estimated that today about 60% of the total world population in treatment relies on herbs and natural products that are thus recognized as an important source of drugs [1]. Phytochemistry studies a huge variety of organic substances that have been discovered and which accumulate in plants. Furthermore, phytochemistry is also defining the structure of these compounds, their biosynthesis, metabolism, natural distribution, and biological activities [2]. An important place among them is occupied by aromatic plants, whose aroma is associated with the presence of essential oils and complex mixtures of volatile compounds, dominated by mono- and sesquiterpenes. In addition to essential oils, aromatic plants are characterized by the presence of plant phenolic compounds, primarily coumarins and phenylpropanoids, that have been shown to possess multiple pharmacological activities. Investigations of these secondary biomolecules intensified when some commercial synthetic antioxidants were found to exhibit toxic, mutagenic, and carcinogenic effects [3]. It was also found that excessive production of oxygen radicals in the body initiates the oxidation and degradation of polyunsaturated fatty acids. It is known that free radicals attack the highly unsaturated fatty acid membrane systems and induce lipid peroxidation, which is a key process in many pathological conditions and one of the reactions that cause oxidative stress. Particularly, the biological membrane lipids in the spinal cord and brain are vulnerable, because they contain high levels of polyunsaturated fatty acids. Moreover, the brain contains significant amounts of transitional prooxidant metals and consumes a lot of oxygen. These features facilitate the formation of oxygen radicals involved in the processes of aging, Alzheimer's and Parkinson's disease, ischemic heart damage, arthritis, myocardial infarction, arteriosclerosis, and cancer. Phenolic antioxidants "stop" free oxygen radicals and free radicals formed from the substrate by donating hydrogen atoms or electrons. Many plant species and aromatic plants have been tested because of their antioxidant and antiradical activities [4].

organisms and its ability to easily receive electrons, free radicals of oxygen origin start more reactions in the cell. The reactions responsible for their formation are respiration, processes of autoxidation of hydroquinone and catecholamine, reduced transition metals, some herbicides and drugs, as well as irradiation that causes water

Any disorder of oxygen species' regulation resulting from a disturbance in the balance between the formation of reactive oxygen metabolites and their elimination by the antioxidant protection system is the state of oxidative stress. In oxidative stress, the formation and accumulation of reactive metabolites are increased, resulting in oxidative processes of destruction of cellular components and genetic

ROS, RNOS, and LP are considered to be the major contributors to the etiology of atherosclerosis and various chronic disorders such as coronary disease, stroke, and ischemic dementia [9]. Antioxidants introduced through food can reduce the occurrence of cardiovascular diseases by inhibiting the production of free radicals and oxidative stress, protecting LDL from oxidation and aggregation, and inhibiting

Oxidative stress often occurs in the brain, because although it represents only 2% of the body weight, the brain uses up to 20% of oxygen added. Also, the brain contains large amounts of polyunsaturated fatty acids subject to lipid peroxidation

Although there are insufficient facts to confirm that the presence of free radicals is necessary in the process of carcinogenesis, it is clear that they can lead to mutations, transformations, and cancers [13]. Regarding the development of cancer, the most important target for ROS is DNA. Carcinogenesis is the result of successive mutations in DNA molecules leading to uncontrolled growth and cell phenotypic modification. One of the first steps in this process is the direct interaction of electrophiles or free radicals with cellular DNA in which promutagen lesions develop. If no repair is performed, these lesions result in mutations in the next generation of cells [14]. An increased intake of antioxidants through diet or dietary

A reduced amount of free radicals or a reduction in the speed of their production

postpones the aging process and a whole series of diseases related to the aging process [15]. A certain maximum life potential characterizes each animal species. There is a reciprocal correlation between the speed of oxygen consumption (and therefore the production of free radicals) and the maximum life potential. Some studies have shown that the aging process can be slowed by increased food intake

2.1 The role of ROS and RNOS in the onset of many diseases

Flavonoids and Phenolic Acids as Potential Natural Antioxidants

DOI: http://dx.doi.org/10.5772/intechopen.83731

decomposition.

material.

2.1.1 Cardiovascular disease

2.1.2 Neurodegenerative diseases

2.1.3 Carcinogenesis

2.1.4 Aging

129

the synthesis of proinflammatory cytokines [10].

under conditions of high oxygen concentration [11, 12].

supplements is associated with a reduction in the onset of cancer.

The aim of this chapter was to show the antioxidant role of phenolic acids and flavonoids presented in aromatic plants and to assess their potential capacity as scavengers of different free radicals.

#### 2. Oxygen as a toxic molecule

Atmospheric oxygen (O2) is present as a biradical with two unpaired electrons, which have the same spin quantum number and are located opposite the orbited orbits. This electronic structure of molecular oxygen determines its chemical reactivity and allows the absorption of individual electrons, with the formation of numerous intermediate, partially reduced oxygen species that are commonly referred to as reactive oxygen species (ROS) [5, 6]. These reactive oxygen species are able to react with basic cellular structures and biomolecules [7] and are responsible for the emergence of many diseases and degenerative damage [8].

The normal concentration of free radicals in the body is very low. However, the effects are very disruptive, as the chain reaction allows one free radical to cause changes in thousands of molecules and damage DNA, RNA, and enzymes in cell membranes and leads to the formation of lipoxygenation products before being inactivated. Which part of the cell (proteins, nucleic acids, membrane lipids, cytosolic molecules) or the extracellular component (hyaluronic acid, collagen) will react with free radicals depends on the nature of the radical and the site of its formation (e.g., cytosolic membranes, mitochondria, endoplasmic reticulum, peroxisome, cell membranes). Due to the presence of molecular oxygen in aerobic

#### Flavonoids and Phenolic Acids as Potential Natural Antioxidants DOI: http://dx.doi.org/10.5772/intechopen.83731

organisms and its ability to easily receive electrons, free radicals of oxygen origin start more reactions in the cell. The reactions responsible for their formation are respiration, processes of autoxidation of hydroquinone and catecholamine, reduced transition metals, some herbicides and drugs, as well as irradiation that causes water decomposition.
