1.1 INTRODUCTION
The customary structure of medication in which plant derivatives are the chief ingredients has gained worldwide recognition and popularity. The practice of herbal therapy in treating diseases and different disorders for meeting primary health needs is thought to be very effective and safe within prescribed doses. Some recent applications of the early customary scheme of treatment may be cited as Pacific yew (Taxus species) that had made quite an impact in the previous decade by providing raw materials to fight against certain types of cancer. Discovery of Ginseng and its therapeutic properties is also noteworthy. Another example is goldenseal (Hydrastis canadensis). The most significant development of anti-malarial drug in current ages was based on a traditionally used plant Artemisia annua L. Its medicinal properties had been well known in China for more than 2000 years. Medicinal plants as cultivated and collected form the basis of numerous phytomedicines in several countries and are thus a big business indeed. Recently, there has been tremendous upsurge in the interest on plants used by the tribal people or are a part of the ancient systems of medicine such as Ayurvedic, Unani, Chinese, Tibetean and the Aztech (South American). The reasons for such interest are mainly the safety, nominal side effects and trials of centuries. The modern approach to the science of ethnobotany evolved in India, USA, France, South East Asia, China, Jamaica, Combodia, Nepal, Hawai, Turkana, etc. are also engaged in the detailed ethnomedicinal studies of the tribal and aborginal populations of their countries (Gupta and Prakash, 2014; Haidan et al., 2016).
Medicinal and aromatic plants provide various kinds of medicines besides supplying nutrition for the preclusion and management of ailments and constitute an integral part of traditional medical prescriptions. From folk medicine and traditional scheme of drug, medicinal florae were adopted into the contemporary scheme of medication after they have been found effective drugs through chemical and pharmacological screening in the initial stages of growth of contemporary medicine plants. Medicinal plants have been quantified to encompass around 10,000 species and account for roughly 50% of all the higher flowering plant species in India alone. Curative properties of few such plants have been described; however, a large number of plants still used by native folklore are to be unraveled. Ayurveda, Siddha, Unani and Amchi systems of medication offer a good base for scientific investigation of medicinally significant molecules from the environment. Evolving notion of joining Ayurveda with the advanced drug discovery programme is worldwide acceptable. According to the reports of the World Health Organization (WHO), about three quarters of the world’s populace presently practise herbs and other customs of customary medicines to treat sicknesses. Customary medicines are broadly used in India and China, and the use of herbal medicines has improved histrionically in the past two decades all over the world (Chikezie and Ojiako, 2015).
Ayurveda (ayus—life, veda—knowledge, meaning science of life), the Indian customary health care system, is the primogenital medicinal system in the world. It offers a method to prevent and treat diverse ailments by a huge number of therapeutic measures and pharmaceuticals. During the previous few eras, intensive search for plant constituents of potential medicinal importance was being pursued all over the world. The therapeutic value of a plant depends on the occurrence of active principles, which exert impact on the structure or role of the living being. These substances are of varying chemical groups, and several of them are useful in the pharmaceutical industry. This natural system is more accessible and devoid of severe side effects, since the plants are well tested over the centuries. From traditional medication and the traditional system of medicine, medicinal plants were adopted into the modern system of medicine after they have been found effective drugs through chemical and pharmacological selection in the initial stages of development of current medication (Pan et al., 2011).
The activity of medicinal plants depends on phytochemicals present in them, though it is, in general, the outcome of the combined activity of several active composites as well as of inert accompanying substances. These inert components might influence bioavailability, stability, and can minimize side effects or might have additive/synergestic effect. The aim of chemical evaluation of traditional medicines is obviously to ensure their therapeutical efficacy and to establish chemical parameters for the standardization and quality governor of the herbal/Ayurvedic finished/end products. Chemistry of natural produces is a research field with endless potential and is especially important in countries that possess great biodiversity. Nowadays, the customary medication all over the world is revalued by an extensive activity of investigation on diverse herbal species and their beneficial properties. The therapeutic properties of florae have been explored in the light of current technical advances throughout the world, due to their potent pharmacological activities, low toxicity and commercial feasibility (Acharya and Shrivastava, 2008; Bjelakovic et al., 2014).
The Rasayana in ayurveda not only focuses on drug remedy but also includes the practice of revitalization and nutrition, including its movement, circulation and perfusion in the body tissues. In reference to the Rasayana drug therapy, the strong antioxidant activity of any Rasayana has been reported; these compounds were found to be several folds more powerful than synthetic molecules (Bjelakovic et al., 2014; Forman et al., 2016). Phytochemical constituents of a plant play a key role in biological activities of different medicinal plants and are accountable for their effectiveness.
Reactive oxygen species (ROSs) are generated by normal metabolic processes in all oxygen-utilizing organisms. Damage induced by ROSs includes DNA mutation, protein oxidation and lipid peroxidation, contributing to the growth of cancer, diabetes, atherosclerosis, inflammation and premature ageing. Antioxidant properties elicited by plant species have a full range of perspective applications in human healthcare. Natural antioxidants such as carotenoids, tocopherols, ascorbates and polyphenols are generally found in plants, foods, vegetables, fruits, herbs and spices containing many compounds with strong antioxidant activities (Kota et al., 2018).
1.2 FREE RADICALS AND HUMAN HEALTH
In the situation of a disturbed balance between the formation of free radicals and antioxidant defense, in the cell we have oxidative stress and the free radicals that can play a part in the growth of many ailments. The over-production of ROS has been involved in the etiology of neurodegenerative diseases such as cardiovascular, diabetes, cancer, Alzheimer’s, retinal degeneration, ishemic dementia and other disorders due to ageing. There are strong indications that antioxidant supplements can ameliorate such conditions (Carocho et al., 2018). They are known to act as antioxidant to defuse toxic free radicals, anti-allergic, anti-inflammatory, immuno-stimulant and anti-hepatotoxic. Specifically, phenols may help to lower the risk of cancer, cardiovascular diseases, age-related vision disorders, asthma and reduce inflammation (Poprac et al., 2017).