A review on saponin: plant derived natural surfactants

A review on saponin: plant derived natural surfactants: History

Subjects: Chemistry, Applied

Contributors:

With increasing environmental concern, there is a trend of replacing synthetic products with their natural equivalents all across the globe [1]. However, it is a grand challenge of the present generation, not merely due to the scarcity of their availability, but due to their high extraction and processing costs compared to the manufacturing of their synthetic equivalents [2]. Along these lines are a group of synthetic chemical compounds known as surfactants. Surfactants are usually known as the major components of household detergents and cleaning products [3]. It has the ability to reduce the surface tension of water, thereby enhancing its cleansing ability. Besides, they also find their application as emulsifiers, wetting agents, dispersants and foaming agents in cosmetics, personal care products, food, and paper processing, oilfield field chemicals, agricultural chemicals, pharmaceuticals, textiles, emulsion polymerization, and many other markets as well [4][5]. Owing to their widespread application in diverse fields, surfactants are among the most produced industrial chemicals. This far huge variety of surfactants have been synthesized to meet the demand of consumers. These synthetic surfactants are largely based on petrochemical raw materials [6]. Because of their petrochemical origin, they are mainly toxic and non-biodegradable, causing many detrimental effects on the environment [7].

Nevertheless, we have natural surfactants that stand out as eco-friendly and sustainable alternatives to their synthetic equivalents. However, at present, the choices are limited and the available product aesthetics do not offer good cleansing activities that the synthetic formulations do. Natural surfactants, as the name suggests, are of natural origin i.e. derived directly from nature either from plants or animal sources [8]. Based on their origin, natural surfactants are broadly classified into two categories: (i) plant-derived natural surfactants and (ii) natural surfactants produced by the fermentation of natural substrates like alkanes, oil, sugars, and wastes in the presence of microbes such as bacteria or yeast, usually termed bio-surfactants [2]. The production of biosurfactants, however, requires valuable carbon sources as raw materials, which are expensive and also a major food source for animals and humans [9]. Providently, plants remain largely untapped sources of natural surfactants. Therefore, more research is to be carried out particularly in exploration, extraction, and isolation of natural surfactants from plants distributed widely in nature.

natural surfactants
synthetic surfactants
eco-friendly

Plants synthesize an unlimited number of bioactive chemical substances [10] that are less toxic and biodegradable than synthetic ones. Among the various bioactive chemical compounds derived from plants, saponins are the ones that exhibit surface-active properties [11]. In fact, they belong to a class of nonionic surfactants [8]. They got their name “saponin” derived from Latin word sapo, which means soap as they form soapy lather when agitated with water [12]. Structurally, they are composed of hydrophilic glycone moieties (sugars) glycosidically linked with hydrophobic aglycones moieties (steroids or triterpenoids [13]. This structural feature resembles that of a typical surfactant and hence attributes to their surface-active properties. Based on the aglycone counterpart of saponins, they are classified as (i) steroidal and (ii) triterpenoidal saponins [14]. Steroidal saponins are further classified as (i) spirostanols and (ii) furostanols glycosides [15]. Triterpenoidal saponins are most abundant in the plant kingdom [16]. Furthermore, phytochemical studies have reported the presence of saponins in more than 100 families of plants [17].

Figure 1: Chemical Structure of a typical Saponin molecule.[18]

Figure 2: Steroidal agyclones (a) Spirostanol (Diosgenin) (b) Furostanol (Protodiosgenin) [19]

Figure 3: Terpenoidal agyclone [18]

On the basis of the number of sugar units (glycone) attached to the agyclone saponins are classified as (i) monodesmosidic saponins: a single sugar unit attached to carbon-3. (ii) bidesmosidic saponins: two sugar unist , one attached to Carbon-3 and other attached to Carbon-26 or to Cabon-28.(iii) Tridesmosidic saponins: three sugar units attached to the agyclone, but are rarely found [18][20]. The sugar units attached to the agyclone may be linear chains or branched chains, which are mainly D-glucose D-galactose, L-arabinose, L-rhamnose, D-xylose, D-fructose or D-glucuronic acid [21][22].

Figure 4: (a) Monodesmosidic triterpenoid saponin and (b) Bidesomsidic triterpenoid saponin. [16]

Table 1: List of some saponin rich plants traditionally used as natural surfactants.

Scientific Name	Common Name	Parts Used
Saponaria officinalis	Soapwort	Roots and Leaves
Chlorogalum pomeridia	Soap root	Root
Quillaja saponaria	Soap bark	Innerbark
Sapindus saponaria	Soap berry	Seed
Sapindus mukurossi	Soap nut (Reetha)	Fruit pericarp

[19][23]

Table 2: List of some saponin rich plants that could be a potential source of natural surfactants.

Scientific Name	Common Name	Parts Used	References
Acacia concinna	Shikakai	Pod and bark	[23]
Acorus gramineus Aiton		Leaf	[23]
Aesculus assamica		Leaf	[23]
Aesculus indica	Indian horse chestnut, Kanor, Bankhor	Fruit	[24]
Agave americana L.	Agave, Bara Kunwar, Kantala, Ran Ban	Leaf	[24]
Agave offoyana		Flower	[18]
Allium nigrum L		Root and Leaf	[18]
Asparagus adscendens Roxb.	Sansban, Saunspali	Fruit and root	[24]
Asparagus racemosus Willd.	Shatavari	Root	[24]
Beaucarnea recurvata		Leaf	[18]
Bupleurum chinense		Root	[18]
Camellia sinensis	Tea	Seed	[24]
Caryocar villosum		Stem	[18]
Chiococca alba		Root	[18]
Cissus modeccoides		Leaf and stem	[23]
Cissus repen		Stem	[23]
Chlorophytum borivilianum	Safed musli	Leaf	[24]
Dillenia parviflor		Fruit	[23]
Harpullia austro-caledonica		Bark	[18]
Garcinia sp.		Fruit	[23]
Garuga pinnata Roxb		Leaf	[23]
Lonicera japonica Thunb.	Honeysuckle	Leaf	[24]
Luffa cylindrica		Fruit	[23]
Microcos tomentosa		Leaf	[23]
Momordica charantia		Fruit and stem	[18]
Oryza sativa L.		Peel	[23]
Oxalis corniculata		Leaf and stem	[23]
Salix tetrasperma		Pericarp	[23]
Sapindus rarak		Fruit	[23]
Sesamun orientale		Leaf	[23]
Silene inflata Sm.	Bigru	Root	[24]
Silphium asteriscus		Leaf and stem	[18]
Solanum xanthocarpum		Fruit	[18]
Tribulus terrestris		Fruit	[18]
Yucca schidigera Roez	Yucca	Bark	[1] [18]

Besides their surfactant properties, they are also reported to exhibit a lot of useful biological activities such as antimicrobial, antioxidant, antifungal, anti-inflammatory, anti-cancer, and cholesterol-lowering properties [17].

Because of their excellent surface activity, biological activities, and wide distribution in nature, saponin rich plants deserve deeper insight as a potential source of natural surfactants [23] as they possess the potential to replace toxic synthetic surfactants abundant today.

References

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