Advances in Extraction and Applications of Bioactive Phytochemicals

By Mihir Kumar Purkait, Dibyajyoti Haldar and Prangan Duarah

Advances in Extraction and Applications of Bioactive Phytochemicals presents comprehensive and systematic coverage of extraction techniques for bioactive phytochemical compounds and their delivery and therapeutic effectiveness. Sections focus on the pharmaceutical industry’s perspective, aiming at compiling recent advances of natural products in the field of drug delivery, including a brief overview of plant-based bioactive molecules, utilization of different plant elements for the extraction of phytochemicals, a compilation of conventional extraction approaches, advanced extraction methods, including Supercritical carbon-dioxide extraction, computational methods to improve production, drug delivery aspects of bioactive phytochemicals, their therapeutic effectiveness, and more.

This book is a complete reference targeted at pharma researchers in academic and corporate environments and those willing to apply the most current extraction methods and health applications. Researchers in medicinal chemistry and chemical engineering will also benefit from this comprehensive resource.

• Offers a consistent compilation of the most current phytochemical extraction techniques
• Includes detailed protocols for extraction
• Covers the main classes of naturally occurring bioactive phytochemical compounds

• Language: English
• Publisher: Academic Press
• Release date: Nov 30, 2022
• ISBN: 9780443185366

Mihir Kumar Purkait

Dr. Mihir Kumar Purkait is a Professor in the Department of Chemical Engineering at the Indian Institute of Technology Guwahati, Assam, India. His current research activities are focused in four distinct areas viz. i) advanced separation technologies, ii) waste to energy, iii) smart materials for various applications, and iv) process intensification. In each of the area, his goal is to synthesis stimuli responsive materials and to develop a more fundamental understanding of the factors governing the performance of the chemical and biochemical processes. He has more than 20 years of experience in academics and research and published more than 300 papers in different reputed journals (Citation: >16,000, h-index = 74, i-10 index = 193). He has 12 patents and completed 43 sponsored and consultancy projects from various funding agencies.

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Chapter 1: Pharmaceutical prospects of plant-based bioactive molecules

Abstract

Secondary metabolites from plants are abundant in bioactive phytochemicals that have been shown to offer a variety of health advantages in both human and animal health. Phytochemicals may be found in a wide range of plant-based foods, including vegetables, fruits, grains, seeds, nuts, and legumes. Recent research on phytochemicals shows that they might be a valuable source of disease-fighting therapeutics and preventatives. The sorts of foods that include these bioactive components are functional foods that, when ingested in a regular and consistent manner through diet, can deliver desired health advantages beyond their inherent features. Alternatively, consumers can get concentrated dietary supplements that offer a specific bioactive phytochemical or a collection of phytochemicals. The chemical and physical characteristics of certain essential bioactive phytochemicals are discussed in this chapter. Techniques for determining phytochemical bioavailability, bioaccessibility, and bioactivity have also been briefly explored.

Keywords

Alkaloids; Pigments; Polyphenols; Steroids; Terpenes

1.1. Introduction

Nature has been exploited by people in the hunt for food and bioactive substances to use as poisons and to cure various illnesses from the dawn of time. Photosynthetic organisms on land and at sea have the ability to collect carbon dioxide and use their numerous sophisticated mechanisms to make bioactive compounds when combined with natural light and water. Plants have historically been the most important source of such compounds [1,2].

We have grown more vulnerable to a wide range of life-threatening illnesses due to our shifting diets and lifestyles. In this scenario, various plant-based products such as vegetables, fruits, and seeds, in particular, may help avoid chronic diseases such as malaria, hypertension, inflammatory bowel illnesses, cancer, coronary heart disease, diabetes, and other diseases caused by pathogens, to name a few. Macronutrients (comprising calcium, magnesium, phosphorus, sulfur), micronutrients (such as iron, copper, manganese, zinc, sodium, molybdenum, and boron), a protein with essential amino acids, dietary fiber, and vitamins are all found in plants, and their presence aids the human body's defenses against pathogens like bacteria, viruses, and parasites. Furthermore, compounds found in plants have significant antioxidant activity, which helps to boost immunity and reduce age-related health problems [3,4]. Various studies have been conducted throughout the years to better understand the advantages of such compounds. Additionally, the separation, purification, and structural identification of single compounds from plant extracts have become possible due to the advancement of analytical methods, such as gas chromatography, nuclear magnetic resonance spectrometry, mass spectrometry, and high-performance liquid chromatography. These cutting-edge methods aid in identifying a broad spectrum of physiologically active molecules known as phytochemicals. These phytochemicals are nonnutrient bioactive molecules produced by secondary metabolism in plants that operate as a defense system, protecting them from pest and disease infections, environmental pressures such as drought and salt stress, ultraviolet (UV) exposures, and other harmful situations [5]. They vary from primary metabolic substances in that they are exclusively formed in particular cells and are not produced by either catabolic or anabolic metabolism [6].

Many studies show that phytochemicals can reduce the risk of major noncommunicable chronic illnesses if taken daily. Many live cells interact with bioactive phytochemicals that prevent DNA damage while slowing the formation of aberrant or damaged ones, such as cancerous cells, by reducing their ability to divide and multiply. There are several ways phytochemicals work against tumors, including destroying rapidly proliferating cells, decreasing oxidative stress, altering the function of growth hormones in cells, inducing apoptosis, and blocking the formation of new blood vessels in malignant tissues. Due to their pharmacologic effects and the fact that they are nontoxic to human cells, they might serve as essential sources for producing drugs to treat a variety of malignancies and other disorders.

To prevent oxidative stress in cell, components including proteins, nucleic acids, and lipids, antioxidants must be present. Antioxidants work by inhibiting the generation of reactive oxygen species or free radicals during various metabolic processes. As a result, a diet rich in plant-based foods provides a wide range of phytochemicals, which are well-known to protect against disease. A wide variety of phytonutrients, including polyphenols, organosulfur compounds, terpenes, steroids, etc., may be found in vegetables and other plant-based meals. The advent of high-sensitivity analytical tools has made it feasible to detect and extract these phytonutrients, as well. It is possible to extract phytochemicals, compounds found in plants, from a wide variety of plant parts and then conduct in-depth analyses to see whether they may be used to treat or prevent certain health conditions [7].

Some of the most important phytochemicals and the biologic roles they play are covered in this chapter. Additionally, various physical and chemical properties of phytochemical groups are highlighted. The chapter also emphasizes analytical methodologies for assessing the bioavailability and bioaccessibility of bioactive substances.

1.2. Overview and structural compositions of naturally occurring bioactive phytochemical compounds

1.2.1. Polyphenols

For treating metabolic syndrome in vitro and in vivo, polyphenols, which are found in many plants, are the most active ingredients. The biologic efficiency of these compounds has been the subject of several studies and reviews. In general, polyphenols are naturally occurring chemicals that share phenolic structural characteristics chemically. As a collective name, polyphenols encompasses a variety of chemicals, although the term has been misused, and its inferred chemical structures have proved ambiguous to researchers. In the scientific community, the word polyphenols is used to describe plant polyphenols, whereas plant phenols is also used to describe the same by some researchers. The term polyphenols is still favored for corporate communication, according to Quideau et al. [8]. According to this definition, the term phenols encompasses the arene ring and its hydroxy substituents, and the term polyphenol should be limited to structures with at least two phenolic moieties, regardless of the number of hydroxy groups they each contain [8].

One of the most abundant and widely dispersed families of secondary metabolites in plants is phenolic compounds. Polyphenols include compounds not only with a polyphenol structure but also molecules with only one phenol ring, such as phenolic acids and phenolic alcohols, as previously discussed. Although polyphenols are technically defined as compounds having phenolic structural properties, they are a varied collection of natural products that include various subgroups of phenolic compounds. Biogenetically, phenolic compounds are generated by two metabolic pathways: the shikimic acid pathway, which produces phenylpropanoids primarily, and the acetic acid pathway, which produces simple phenols primarily. Carbon from photosynthesis is believed to be used to produce between 100,000 and 200,000 secondary metabolites. The phenylpropanoid pathway, which is used to make most phenolic compounds in plants, accounts for approximately 20% of all carbon used in photosynthesis [9]. Flavonoids, the most abundant category of phenolic chemicals in nature, are formed when both processes are combined. Condensed tannins or nonhydrolyzable tannins are created along the biosynthetic routes to flavonoids production, among the not well-understood condensation and polymerization stages. Gallic acid or hexahydroxydiphenic acid derivatives are examples of hydrolyzable tannins. Polyphenols may be connected with numerous organic acids or with one another, in addition to their chemical variety.

More than 1000 different polyphenolic compounds with a diverse range of structures have been discovered (including over 8150 flavonoids). Phenolic phytochemicals are classified into three groups based on their dispersion in nature: those that are broadly dispersed, those that are widely distributed, and those that are polymeric. Similarly, based on the chemical structure, polyphenols can be divided into three distinct categories (phenolic acids, flavonoids, and nonflavonoids), as shown in Fig. 1.1 [10,11].

Aglycone-based categorization is the most used method of categorizing polyphenols. However, polyphenolic substances can be categorized in a variety of ways following this approach. Harborne [12] classified phenolic chemicals into 16 primary classes based on their carbon chain, as shown in Table 1.1.

Apart from the chemical categorization, researchers classify polyphenols according to the amount of phenol rings they possess and the structural features that connect the rings (Fig. 1.2). Moreover, the list of polyphenolic categories is nonetheless consistent. Of all the phenolic chemicals found in plants, flavonoids are by far the most prevalent and well researched. Anthocyanidins, flavones, isoflavones, flavonols, flavanols, flavones, and flavanones are among the most significant flavonoid groups, which are further classified by the degree of hydroxylation and the existence of a C2–C3 double bond in heterocyclic pyrone rings. There are considerable structural changes in the three-ring structures of these compounds depending on the degree of hydrogenation and hydroxylation that has occurred in these groups [14]. About 8000 compounds of flavonoids have been identified so far, many of which are sulfate or methylated, conjugated with mono- and disaccharides, lipids, amino acids, carboxylic acids, and organic acids [15].

Phenolic acid is another popular type that belongs to the group polyphenols. One or more of the following groups can be found in the molecular structure of phenolic acid: carboxylic group, benzenic ring, hydroxyl, and/or methoxyl groups. Phenolic acid can be broadly categorized into two types, i.e., benzoic acids and cinnamic acids. Benzoic acid is one of the simplest phenolic acids found in nature, with seven carbon atoms (C6–C1). Cinnamic acids (C6–C3), which have nine carbon atoms, are seldom seen in plants in their free form.

Figure 1.1  Classification of polyphenols based on their chemical structure [10].

Figure 1.2  Plant polyphenols and polyphenolic groups classified by number of phenol rings and structural components. Reproduced with permission from Cvitanović et al. [13].

Table 1.1

A cyclic alcohol acid is usually seen in combination with the ester form of these compounds. Caffeoyl ester is the most important combination of neochlorogenic acid, isochlorogenic acid, chlorogenic acid, and cryptochlorogenic acid, all of which are esters that include cyclic alcohol-acids like quinic acid and cinnamic acid [16]. Phenolic acids, in fact, constitute one-third of all phenolic compounds found in the human diet, according to Yang et al. [17]. The quantity of hydroxyl groups in phenolic acids and their esters influences their antioxidant activity. Among the two types, cinnamic acids that have been hydroxylated are more efficient than benzoic acids in general.

Other forms of polyphenols found in dietary sources include lignans and stilbenes. Two phenylpropane units make up lignans. Linseed, which provides secoisolariciresinol (up to 3.7g/kg dry wt.) and modest amounts of matairesinol, is the most abundant dietary source. Linseed has up to 1000 times more lignans than dairy products as well as other cereals, grains, fruits, and vegetables [18]. Stilbenes are found in tiny levels in the human diet, yet they are beneficial. Wine contains many antioxidants, one of which, resveratrol, is found in modest concentrations (15mg glycosides/L in red wine and 0.3 to 7mg aglycones/L in white wine) and has been extensively studied for its anticarcinogenic qualities [19].

1.2.1.1. Properties of polyphenols

Polyphenols have a diverse variety of qualities depending on their specific structural configurations. Based on the vast amount of research available on plant polyphenols and their capabilities, the most important attributes of polyphenols may be grouped into many categories.

For polyphenols, solubility is a critical factor. When the plant phenolics have been entirely esterified, etherified, or glycosylated, polar organic solvents tend to dissolve them. The corresponding aglycones of most phenolic glycosides are water-soluble; however, this is not always the case. Water solubility generally rises with the amount of hydroxyl groups present, with a few notable exceptions.

UV absorption is intense for all phenolic compounds; colorful phenolic compounds also absorb heavily in the visible range [20]. Phenolic chemicals are classified according to their different classes based on their absorption properties. In the 250–290nm range, phenols and phenolic acids exhibit their spectral peak; similarly, at wavelengths of 250 and 350nm, cinnamic acid derivatives exhibit absorption bands of approximately equal strength; flavones and flavonols have absorption bands at around 250 and 350nm that are roughly comparable in strength; chalcones and aurones have a strong absorption peak at 350nm and a weaker band at 250nm. When measured at wavelengths between 475 and 560nm and between 535 and 545nm, anthocyanins and betacyanins show a similar absorption peak, respectively, whereas their secondary absorption peak is 270–275nm. These compounds are secondary metabolites generated by plants, and they are employed to safeguard them against the harmful effects of UV radiation and disease.

1.2.2. Alkaloids

W. Meissner created the term alkaloids in 1818 to describe all organic substances derived from plants that have a basic structure. Later research revealed that alkaloids include a heterocyclic ring system that contains the nitrogen atom. Primary, secondary, tertiary, and quaternary amines are all included in this definition [21]. There have been various scientific breakthroughs since then that have helped shape the characteristics that define this class of substances, which has resulted in numerous chemical structures being introduced into this class. Alkaloids have been found in plants, animals, and microbes, including humans, marine creatures, fungi, and other bacteria. Compounds possessing side chain–bearing nitrogen, nitrogen-containing functional groups, or any combination of these were also categorized as alkaloids because of their neutral nature [22].

It is possible to categorize alkaloids based on their chemical structure, biologic activity, biosynthesis mechanism, and occurrence into heterocyclic and nonheterocyclic alkaloids, as shown in Fig. 1.3.

1.2.2.1. Heterocyclic alkaloids

Fig. 1.4 depicts the basic structure of the naturally occurring alkaloids. Heterocyclic alkaloids have a nitrogen atom in their structure. They are made biosynthetically from the amino acids they are named after, and they are frequently generated after a decarboxylation procedure. Based on the amino acid of origin, six primary categories of alkaloids have been identified so far. L-ornithine, L-tyrosine/L-phenylalanine, L-lysine, L-tryptophan, L-histidine, and glycine/aspartic acid are all derivatives of these amino acids [23]. Derivatives of these primary groups also play a significant role. For example, isoquinoline alkaloids, a derivative of L-tyrosine/L-phenylalanine, are a class of compounds that are among the most diversified natural compound in the world. In their skeleton, they have an isoquinoline or tetrahydroisoquinoline ring that is biogenically produced from phenylalanine and tyrosine [24]. The isoquinoline alkaloids are a diverse category of compounds that are not structurally homogenous. There are eight subgroups within this group (i.e., benzylisoquinoline, aporphine, protoberberine, protopine, benzo[c]phenanthridine, morphinan, phthalideisoquinoline, and emetine alkaloids), each with a distinct degree of oxygenation and intramolecular rearrangement, as well as a varied pattern of distribution and the occurrence of additional rings linked to the main system.

Figure 1.3  Classification of alkaloids.

When it comes to alkaloids, protoberberines represent about a quarter of all structures revealed so far, making them the most common nitrogen-containing secondary metabolites found in nature. Isoquinoline alkaloids may be found in Berberidaceae, Papaveraceae, Fumariaceae, Ranunculaceae, Menispermaceae, Rutaceae, and Annonaceae, as well as in a variety of other plant groups (in the dehydro forms). Plants of the Magnoliaceae and Convolvulaceae families are also rich in these alkaloids [25,26].

Proline and L-ornithine, two amino acids, are shown to be precursors of the alkaloids nicotine, tropane, stachydrine, necine, and pyrrolizidine. Tropane (L-ornithine derivatives), another major alkaloid, is one of the world's oldest plant medicines, with ethnopharmacologic uses including analgesia, hallucinogens, and poisons. Esters (mono-, di-, and tri), tropanes (carboxylated and benzoylated), and ornithine-derived compounds are prevalent in the Solanaceae (family of flowering plants), Convolvulaceae (bindweed or morning glory family), Brassicaceae (a large and commercially significant flowering plant family), Erythroxylaceae (a family of flowering trees and shrubs), and Euphorbiaceae (the spurge family) [27]. Due to a tropic acid residue connected to the ecgonine nucleus as an ester, some of these alkaloids have chiral structures. Racemic mixtures can arise during alkaline extraction, especially when the former exists naturally in its R form (for example, the synthesis of (+)-atropine from (−)-hyoscyamine). Tropanic, benzoic, acetic, tiglic, isobutyric, isovaleric, and anisic acids were all found in the tropane alkaloids, as were a number of other acids. Drugs like scopolamine (a tropane alkaloid) are routinely used to treat digestive and urinary system spasms. Ophthalmologic eyedrops usually contain atropine to increase pupil size, paralyze the accommodation reflex and facilitate ophthalmic examinations. To enhance their appearance, ladies have been using Atropa belladonna juice to make their pupils larger since at least the Renaissance period. However, tropane alkaloids have a long list of adverse effects and contraindications. Cardiac abnormalities, particularly irregular heartbeat, as well as euphoric and disorienting moods, depressed tendencies toward the central nervous system, and dryness of the mucous membranes are all documented side effects. Glaucoma, prostatic hyperplasia, urinary tract illness, and pregnancy should all be avoided [28,29]. The central nervous system action of tropane alkaloids makes them a popular drug of abuse. Cocaine is one of the most well-known of these substances. Cocaine can cause cardiac death at large dosages by blocking sodium channels. In the long run, chronic use might lead to depression, suicide attempts, sleeplessness, or psychomotor retardation. More than 4000 people died as a result of its misuse in 2013. Cocaine's medicinal uses are confined to anesthetic purposes in nasal and lacrimal procedures [30]. The alkaloid's ligand impact on the central nervous system's opioid receptors accounts for its dependence-inducing