Botanical polysaccharides

This is perhaps the most diverse group of polysaccharides. Many of these materials have been known to man for centuries. Guar gum, locust bean gum (LEG), tara and cassia gum are composed of a (1 —+ 4) linked mannose backbone with single galactose substituents and are therefore referred to as galactomannans. They differ in the degree of galactose substitution. 

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Large quantities of polysaccharides are available in nature and many of them display a variety of biological functions [1 ]. There is an abundance of literature on the isolation of bioactive polysaccharides from botanical sources [1-5]. This area of research has attracted a lot of interest due to the fact that most of the bioactive polysaccharides are nontoxic with minimal side effects [4,5]. Hence, this class of biopolymers forms ideal candidates for therapeutic applications. Some of the notable bioactivities of botanical polysaccharides include antioxidant, immunomodulatory, and antitumor properties [4-10]. However, the mechanism of action of these biopolymers is not well understood. In general, one of the primary mechanisms of action of polysaccharides is nonspecific immunomodulation [8]. The key mechanism behind the immunomodulatory, anticancer, antibacterial, and other pharmacological activities of plant polysaccharides is to activate macrophages, which then leads to modulation of the complement system that activates the cells involved in innate immunity and improves host defense [1—4,11,12]. 

Due to minimal side effects of botanical polysaccharides, there is growing interest in the use of such polysaccharides for the treatment of many human diseases caused by oxidative stress such as cancer [5,26]. Due to the fact that herbal polysaccharides that display antitumor properties also possess... 

Botanical polysaccharides exist as structural constituents of plant cell wall [64]. The main types of polysaccharides involved in cell wall are rigid fibrillar chitin (or cellulose) matrix-Uke (3-glucan, a-glucan, and glycoproteins [64-70]. Therefore, the selectirai of an effective extraction procedure for plant polysaccharides will have to depend on the cell wall structure [64]. In general, the basic theory of extraction of polysaccharides from botanical materials is to break the cell wall under certain conditions such as pH value, temperature, irradiation with microwave, and ultrasonic radiation [65,71]. 

Extraction of botanical polysaccharides has traditionally been successfully carried out using the popular method of hot water extraction [1,2,5,71-77,85] and it is applicable in a variety of plant cell wall structures and water solubility of polysaccharide constitutes [65]. Briefly, the procedure involves large quantity of medicinal plant material/mushroom to be powdered, and then homogenized to maintain uniformity within and between the samples collected at different times. The powdered sample is then subjected to hot water extraction by autoclaving for approximately 2 h at 121 °C [5]. Autoclaved sample is filtered after allowing it to cool to room temperature, and the supernatant is then precipitated using 95% aqueous ethanol (supema-tant EtOH=l 4, v/v) for about 15 h at 2.5 °C to remove nonpolar... 

It may be emphasized again here that the botanical polysaccharides with immunomodulatory properties are also known to be potent antioxidants [5,27]. Many studies have shown that the oxidative stress producing free radicals lead to both initiation and promotion of multistage carcinogenesis [25,35]. These findings suggest that the plant polysaccharides, which are natural antioxidants, immunomodulators as well as antitumor agents, are expected to be the future chemotherapeutics of choice. 

Future research also deserves a greater emphasis on detailed understanding of anticancer mechanism of botanical polysaccharides to evaluate the relationship of structure of polysaccharides to their function which are the issues that are yet to be fully uncovered. 

Schepetkin, lA Quiim, MX. Botanical polysaccharides Macrophage immunomo-dulation and therapeutic potential. International hnmunopharmacology, 2006, 6, 317-333. 

The botanical gums represent a family of polysaccharides obtained from a wide variety of plant sources. They are subdivided into exudate gums, seed gums, and gums obtained by extraction of plant tissue. For a gum to be used in commercial quantities, it must be present in the tissues or be readily extractable in relatively pure form which limits the number of commercial botanical gums. 

Starch granules are composed of two types of a-glucan, amylose and amylopectin, which represent approximately 98-99% of the dry weight. The ratio of the two polysaccharides varies according to the botanical origin of the starch. 

Amylose, a linear, high molecular weight (l- -U)-a-D-glucan, is one of the principal polysaccharides of starch. Because of the longstanding utility of starch as a raw material, and its widespread botanical availability, its structure and properties have been studied for centuries. Since the more recent realization that almost all varieties of starch are composed of two polysaccharides - the linear amylose and the branched amylopectin - a significant share of interest has shifted to the study of these components. Of particular interest has been the observation that both components occur naturally in crystalline form in the starch granule. 

Plant gums, which occur as exudates on the bark or leaves of trees, are salts of polyuronic acids and are usually freely soluble in water. It is often difficult to decide whether such polysaccharides are homogeneous, but a beginning has now been made in the determination of their structures. Weak linkages have been shown to be present, and it is possible to remove portions of the molecules that are readily hydrolyzable by mild acid, leaving a more stable acidic residue. The structure of the gums appears to depend upon the source, and some studies are complicated by the fact that the botanical origin of the gum was not known with certainty. 

The nature of the antitumor action of a polysaccharide is not entirely clear, but certain bacterial polysaccharides may directly attack tumors, as evidenced by the resulting intratumoral hemorrhage and necrosis. On the other hand, most of the polysaccharides from other botanical sources cannot be shown to exert any direct action on tumor cells. Their antitumor action must, therefore, be considered to be dependent upon the reaction of the host that is, their effect is host-mediated. It is possible that, in some instances, these two types of action may be interwoven. The discussion in this Section covers only those polysaccharides that effect a host-mediated reaction. 

There is, in fact, no standard method of separating a polysaccharide mixture a combination of several techniques gives the best chance of success. Each botanical source presents its own problems, and the task of separation may be diflicult and experimentally tedious it provides no rapid results, but is an essential preliminary to structural investigations. 

Starch is a naturally occurring biopolymer in which glucose is polymerized into amylose, an essentially linear polysaccharide, and amylopectin, a highly branched polysaccharide. Starch occurs in plant tissues in the form of discreet granules whose size, shape, and form are unique to each botanical species (Woolfe, 1992). Sweet potato roots contain approximately 80-90%... 

Pectins are probably the most complex polysaccharides known, in terms of their chemistry and are certainly so in terms of their biosynthesis. Classically they were regarded as al,4-galacturonans, with various degrees of methyl esterification, and the terms pectic acid and pectinic acid referred to the non-esterified and partially esterified forms respectively. A third term protopectin , was used of insoluble pectin that could not be extracted from plant cell walls by hot solutions of chelating agents. It was considered that these three classes of pectin constituted a pectic triad . This view is now known to be erroneous, but it is still frequently put forward, especially in botanical texts. Consequently any discussion of the synthesis of pectins must be prefaced by a description of their chemistry, as it is now understood. 

The botanical materials are usually powdered, and then hot water extraction is performed [72-79]. This will be, occasionally, performed in combination with certain supplementary procedures that include microwave [80-82] and ultrasonic radiation for the effective extraction of polysaccharides from botanical... 

Microwave-Assisted Extraction of Polysaccharides As mentioned earlier, hot water extraction followed by some of the supplementary methods such as microwave- and ultrasonic-assisted tissue degradation techniques will be beneficial for the effective extraction of polysaccharides from botanical material [81-84]. Occasionally, these supplementary methods are employed directly without subjecting the plant material... 

The literature demonstrates that ultrasonic extraction is more efficient with shorter extraction time than the classical method and provides higher yield (Table 1) [71]. This was confirmed by the extraction of polysaccharides from mulberry leaves using ultrasonic method [87]. UAE is therefore a promising alternative technique for the extraction of natural polysaccharides from botanical sources [87,89]. Correct use of UAE method preserves the structural elements of the extracted polysaccharides. If the applied ultrasonic power, irradiation time, and reaction temperature are too high, the extracted polysaccharides are likely to degrade and their structures may not be preserved which leads to changes in their biological properties [89]. 

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