Status Natural Compounds of Medicinal Plants, Herbs, and Spices: Polyphenols, Tannins, Volatile Oils

Background

When the activity of SMs is directed at other organisms in the environment, these substances can be considered as “environmental agents” ensuring that producers survive in competition with other organisms that populate the same ecological niche. The data obtained from the analysis of the nucleotide sequence support the concept that the secondary metabolism resulted from changes in the existing pathways of the primary metabolism. Although the amino acid sequence identified deductively from the nucleotide sequence of the corresponding genes is sufficient to indicate a common origin, for the data to be more conclusive, a comparison of genes from different species than from the same species would be necessary. Based on the knowledge gained in the field, a number of clear characteristics of secondary metabolism have been established:

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  SMs are not essential for growth and tend to be strain-specific;

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  these compounds have a wide variety of chemical structures and biological activities;

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  SMs are derived from primary metabolic intermediates through unique biosynthetic pathways. These paths are often long and complex; biochemical reactions are catalyzed by enzymes with substrate specificity different from those of equivalent enzymes of primary metabolism;

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  the formation of SMs is determined by sets of associated genes subjected to a regulatory mechanism that refers both to the level of gene expression and to the moment of its onset;

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  control mechanisms is well integrated with the physiology of the producing organism.

The information obtained in this way suggests that the natural transfer of genes between different organisms was an important factor in the evolution of SMs. Many of the pathways of secondary metabolism may have a very old origin, with changes occurring in them may result from more recent acquisitions of exogenous genetic material in some producing microorganisms. There are many classes of phenol SMs, nitrogen compounds and terpenes. The study of these substances began in the 19^th century, when chemists investigated the use of chemicals in herbs (drugs and poisonous drugs). The largest group of SMs with a role in defense, synthesized by MPHSs are terpenes, these water-insoluble substances, are intermediates of biosynthesis; it is formed by joining units with five carbon-isoprene atoms. SMs are suspected to form as a consequence of natural selection, as only MPHSs can protect themselves from pests, but also due to the biosynthesis of these compounds, plant species can survive. Despite extensive knowledge of anthocyanin biosynthesis and their role in plant life, there are many less elucidated aspects of the genes involved in the biosynthesis of these compounds and the role of encoded enzymes in phenylpropanoid metabolism.

Polyphenols And Tannins

2.1. Polyphenols are classified as antioxidants whose main action is to prevent the formation of free radicals, fighting against skin aging. MPHSs produce a wide variety of NOCs that are not directly involved in the primary metabolic processes of growth and development.

The roles of these NPs in MPHSs have only recently come to be appreciated, in a context of analysis. NPs seem to work primarily to protect against predators and pathogens, but also to provide bait for pollinators and seed distributors, so they are important in breeding.

Natural polyols are hydroxylated derivatives of an alcoholic nature with more than two hydroxyl groups in the molecule. Acyclic and cyclic polyols are common in the plant kingdom. Phenolic NOCs are widely distributed in the plant kingdom. There may be 4,000 polyphenolic NOCs in MPHSs, and only a few of these NOCs (vitamin C and E) are known and studied. Vegetable tissue can contain up to a few grams per kilogram. External stimuli, such as microbial infections, ultraviolet radiation, and chemical stressors can induce their biosynthesis. This class of NOCs can act to create competitive advantage between rival species such as poisons. The classification of phenolic NOCs in MPHSs can be seen in the table 1: