**1.10. Saponins**

oxygen [21]. The compounds have basic properties and are alkaline in reaction, turning red litmus paper blue. In fact, one or more nitrogen atoms that are present in an alkaloid, typically as 1°, 2°, or 3° amines, contribute to the basicity of the alkaloid. The degree of basicity varies considerably, depending on the structure of the molecule, presence, and location of the functional groups [22]. They react with acids to form crystalline salts without the production of water [21]. Alkaloids exist majorly in solid states as atropine, liquids containing carbon,

Alkaloids are mostly readily soluble in alcohol but are sparingly soluble in water though their salts are usually soluble in water. Their solutions are usually very bitter; alkaloids defend plants against herbivores and pathogens and are used widely as stimulants, narcotics, pharmaceuticals, and poisons because of their biological potencies [23]. Alkaloids, in nature, are found in large quantities in the seeds and roots of plants and mostly in combination with vegetable acids. Alkaloids are useful as central nervous system (CNS) stimulants and anesthetics

Alkaloids also find its usefulness as pain relievers [24]. Atropine is an alkaloid used widely in medicine as an antidote to organophosphate poisoning, while caffeine stimulates CNS and respiratory systems. Caffeine also serves as an antidote to barbiturate and morphine poisoning, while emetine (from *Cephaelis ipecacuanha*) root is useful in the treatment of protozoal

The tannin compounds are found mainly in many plant species which help to confer on them protection from predators and probably pesticides; they also help in regulating plant growth [25]. The dry and puckery feeling in the mouth after eating unripe fruits or red wine is attributed to the astringency from the tannins [26]. The destruction or modification of tannins with time in like manner plays an important role in the ripening of fruit and the aging of wine. They are acidic in reaction, and this is attributed to the presence of phenolics or carboxylic group [27]. They form complexes with proteins, carbohydrates, gelatin, and

Tannins are divided into hydrolysable tannins and condensed tannins. Hydrolysable tannins, when hydrolyzed, produce gallic acid and ellagic acid, and depending on the type of acid produced, the hydrolysable tannins are called gallotannins or ellagitannins; when tannins are heated, they form pyrogallic acid [25]. The presence of phenolic group in tannins confers on them their usefulness as an antiseptic [27]. Common examples of hydrolysable tannins

Plants that contain tannins have been reported to be astringent in nature and are useful in treating intestinal disorders like diarrhea and dysentery. This means that tannins possess antimicrobial activity [28, 29]. The antimicrobial activities possessed by these plants could support their use in West Africa for treating gastrointestinal disorders [30]. Tannins are also

include the aflavins (from tea), daidzein, genistein, and glycitein.

hydrogen, and nitrogen.

**1.9. Tannins**

alkaloids.

potent antioxidants [31, 32].

in pharmacological applications [23].

16 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

infections, for example, amoebic dysentery.

Saponins are a class of phytochemicals present in abundance in numerous species of plants. They are specifically amphipathic glycosides and are grouped phenomenologically by their production of soap-like foaming when shaken in aqueous solutions (phenomenology—study of structures of consciousness as experienced from the first-person point of view). They are grouped structurally by possession of one or more hydrophilic glycoside moieties combined with a lipophilic triterpene derivative [33].

Two major groups of saponins exist which are steroid and triterpene saponins. Saponins are insoluble in ether but soluble in water, and on hydrolysis, they give aglycones like glycosides. They cause hemolysis of blood and cattle poisoning as they are known to be extremely poisonous (27). Apart from causing irritation to mucous membranes, they have a bitter and acrid taste. They are soluble in alcohol and water but insoluble in solvents like benzene and n-hexane that are organic and nonpolar; therefore, they are mostly amorphous in nature. Saponins are therapeutically important because they lower bad fats in the body (hypolipidemic) and have anticancer potentials. Saponins work in synergy with the cardiac glycosides [22].

Saponins are known to produce inhibitory effect on inflammation [34]. Saponins help in lowering cholesterol which will subsequently reduce the risk of cardiovascular diseases such as hypertension which usually leads to stroke [35].
