ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ... ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
B2.1.1 B2.1.2.1 Introduction CHAPTER B2-1: SAPONIN LITERATURE REVIEW Many different secondary metabolites are synthesized collectively by plants. This can either be as a response to pathogen attacks and stress or part ofthe plant's normal growth. Although these secondary metabolites are not required for growth and reproduction, they are important in that they offer the plant selective advantages: for example, restraining the growth of neighboring plants or protecting the plant against pests, pathogens and stress (Wink, 1999; Morrissey and Osbourn, 1999). Saponin - chemistry Saponins are a pharmacodynamic group of secondary metabolites with a wide spectrum of biological activities. They are found in more than 90 plant families (Sondhia, 2005), such as peanuts, lentils, lupins, alfalfa, oats and spinach (Fenwick and Oakenfull, 1983; Huhman and Sunmer, 2002; Woldemichael et aI., 2003). Saponins are characterized by surfactant properties because they contain both hydrophobic and hydrophilic components and, in most cases, give stable, soap-like foams in aqueous solutions. Saponins are glycosidic compounds containing a carbohydrate and a non-carbohydrate unit in the same molecule. An acetal linkage joins the carbohydrate residue to a non-earbohydrate residue or aglycone at carbon atom position 1. The sugar component is called the glycone. Saponins are surface-active compounds because of a lipid-soluble aglycone and water-soluble sugar chain(s) in their structure. This aruphiphilic characteristic gives saponins detergent, wetting, emulsifying and foaming properties (Ibanoglu and lbanoglu, 2000; Sarnthein-Graf and La Mesa, 2004; Wang et aI., 2005) 140
The chemical structure ofits sapogenin (aglycone) determines the type to which the saponin belongs - steroidal or tritezpenoid (Figure B2-1.1). Saponins are glycosides because they contain one or more sugar chains attached to the aglycone backbone (Hostettmann and Marston, 1995). Glycone Glycoside (sugar) Saponin Figure B2-1.1: Types ofsaponin (Friedli, n.d) Neutral saponin l Steroids Aglycone Sapogenin Acid saponin l Triterpenoids Both types of sapogenins are synthesized from a similar pathway, involving the head-to tail coupling of acetate units. However, after the formation of the triterpenoid hydrocarbon, squalene (Holstein and Hohl, 2004), there is a split in the pathway that leads to steroids in one direction and to cyclic triterpenes in the other (Figure B2-1.2) 141
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The chemical structure ofits sapogenin (aglycone) determines the type to which the saponin<br />
belongs - steroidal or tritezpenoid (Figure B2-1.1). Saponins are glycosides because they<br />
contain one or more sugar chains attached to the aglycone backbone (Hostettmann and<br />
Marston, 1995).<br />
Glycone<br />
Glycoside (sugar)<br />
Saponin<br />
Figure B2-1.1: Types ofsaponin (Friedli, n.d)<br />
Neutral saponin<br />
l<br />
Steroids<br />
Aglycone<br />
Sapogenin<br />
Acid saponin<br />
l<br />
Triterpenoids<br />
Both types of sapogenins are synthesized from a similar pathway, involving the head-to<br />
tail coupling of acetate units. However, after the formation of the triterpenoid<br />
hydrocarbon, squalene (Holstein and Hohl, 2004), there is a split in the pathway that<br />
leads to steroids in one direction and to cyclic triterpenes in the other (Figure B2-1.2)<br />
141
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