Surfactants are of widespread importance in the detergent industry as well as in the cosmetic industry. Additionally they are used for lubrication, catalysis, and in drug delivery. Common synthetic surfactants can have negative effects, such as skin irritation.
The trend towards natural ingredients is growing and a vegetable-derived surfactant is becoming increasingly desirable and much needed by many “green” formulators. Natural surfactants from soap nut shell fulfil all the relevant requirements on surfactants and provide many additional benefits. The soap nut tree, Sapindus mukorossi, is one of the most important plants in the tropical and subtropical areas in Asia. Native to South India, it grows wild in warm temperate to tropical regions. Belonging to the family Sapindaceae, the genus Sapindus includes between 5 to 12 species. The soap nut tree, also known as Soapberry, has been used traditionally in India to wash clothes and hair. The Indian names for soap nut are Ritha, Doadni, Doda or Dodan. In China and Japan it has been used as a remedy for centuries. In Japan the pericap is called enmei-hi, which means “life prolonging pericarp”, and in China wu-huan-zi, the “non-illness fruit”.1 Sapindus mukorossi is one of the most important sources for saponins. The pericarp contains 10% to 11.5% saponins, and is used locally for protection against pests and microorganisms. Sapindus trifolatus also contains saponins but has smaller fruits that contain less saponin.2 The fruits of Sapindus mukorossi are small orange coloured drupes which are 1 cm to 2 cm in diameter. The ripe fruits are harvested in September/October. After drying the fruits the stickiness disappears and the colour changes to red brown. The fatty seeds are removed, and it is the dried nut shells that provide the source of the saponins. The traditional application of soap nuts is to use the dried peel as it is or it is ground to a powder. A much more convenient application is to include the extracted saponins in detergent or personal care formulations. Saponins are glycosides of hydrophobic alcohols that provide surface activity and form soap-like, foaming solutions in water. Saponins occur in many plants and in some animal products. According to their genin the saponins are classified in triterpensaponins (triterpenoidal saponins) and steroidsaponins (steroidal saponins) (Fig. 1). Most of the natural occurring saponins are triterpensaponins of the pentacyclic Oleanan type. Typically the sapogenins are linked to one (monodesmoside), two (bisdesmoside), and infrequently three sugar chains. Surface activity is generated, if the saponin contains 2-3 monosaccharides.3 The triterpensaponin Hederagenin (Fig. 2) has been identified as the major saponin in the aqueous extract of soap nut shell. The saccharides D-glucose, D-galactose, D-fructose, D-xylose, L-arabinose, L-rhamnose, L-fucose, D-chinovose (6-desoxy-D-glucose), and the uronic acids D-glucuronic acid and D-galacturon acid are found in glycosidic linkage to hederagenin.2,4
Consumer survey
The acceptability of natural saponins from soap nut shell was evaluated in a consumer survey. The online inquiry covered 288 participants, and subjects were 75% female and 25% male. Sixty per cent of the panel was in the age group between 20 and 39 years, and 40% between 40 and 59. The results of the survey show that the ecological aspect is of high importance for consumers, especially in food and personal care segments. There is already a broad awareness of natural detergents, and 36% of the interviewees knew natural detergents. Eighty per 80% of the participants would prefer products partly based on natural detergents to a conventional product. Even more would prefer a 100% natural, vegetable-based detergent instead of synthetic detergents. Main reasons for this decision are protection of the environment and reduction of skin irritations and allergies. However, the cleaning performance of the detergent is the most relevant criteria. Natural surfactants are also preferred in personal care products such as shampoos, shower gels, face cleansing preparations etc. Ninety per cent would use soap nut shell extract in such cosmetic applications. (Table 1). Cleaning performance is the most relevant requirement for a natural detergent. Pre-tests showed that very low ratios of 1.5% to 3.5% of soap nut shell extract are sufficient to wash a drum of laundry with a satisfying result. The strong performance of an aqueous extract of soap nut shell from Sapindus mukorossi was proven in a wash test. Detergent formulations including all necessary additives, builders etc were developed containing soap nut shell extract as a sole surfactant or standard surfactants, respectively. EMPA-test materials were used for the laundry tests being artificially soiled with 6 different standardised soiling compounds. They were washed with the test formulations in order to compare the natural saponin extract to standard synthetic surfactants with respect to cleaning performance. Two detergent product types, a heavy duty and a light duty powder detergent, were applied. Each product came in two formulations, one containing standard surfactants (9.3% and 14.7% active respectively) and the other containing soap nutshell extract as sole surfactant (1.5% and 3.2% respectively) in a much lower amount (Tables 2 and 3). The test was conducted in a common household washing machine. The evaluation was visual. The results show that the formulations solely containing natural saponins from soap nut have an excellent cleaning performance comparable to commercially available standard detergents. Depending on the kind of soil, the degree of purification was slightly varying. In fabrics with sebum and soot /oil was even a trend towards a better removal when using soap nutshell extract in both formulations (Fig. 3). This result is especially remarkable taking into account the difference in the ratio of active surfactant content. In powder detergents the required amount of standard surfactants is 5 to 7 times higher than that of saponines. For liquid laundry detergents the ratio is even higher (10:1). It is also possible to formulate cleaners with soap nut shell extract. The required amount of standard surfactants is 10 times higher than that of saponins. Hand dish wash liquids require adjusting of the viscosity with thickeners. Stability is sufficient in the range of pH 2 to 3 (mild bath and toilet cleaners) up to pH 11 (APC and mild kitchen cleaners).
Additional benefits
Saponins from Sapindus mukorossi provide many additional benefits including antiinflammatory and anti-microbial effects. These benefits are especially useful for personal care applications such as deodorants and anti-dandruff shampoos. The pericarps of Sapindus mukorossi were traditionally used for the treatment of dermatomycoses. Tanaka demonstrated the antimicrobial activity of the crude saponin extract and of hederagenin whereas the crude extract was more efficient.1 The crude extract showed a significant anti-yeast activity. All monodesmosides of hederagenin exhibited a strong growth inhibition against the pathogenic yeast Candida albicans, which causes cutaneous candidiasis. Antidermatophytic activity was observed in hederagenin 3-O-?-L-arabinopyranoside. The saponin fraction inhibited the dermatophytic fungi Trichophyton rubrum, T. mentagrophytes, Sabouraudites canis and Epidermophyton floccosum.1 The saponin fraction showed also moderate antibacterial activity against Gram-positive bacteria and exibited growth inhibition against Malassezia furfur (Pityrosporum ovale),1 a yeast-like anthropophilic fungus associated with dandruff and athlete’s foot. Several in vivo tests show an antiinflammatory activity of crude saponin and hederagenin isolated from Sapindus mukorossi. Crude saponin and hederagenin inhibited the development of carrageenininduced oedema in the rat hind paw as well as on granuloma and exudate formations induced by croton oil in rats. Additional crude saponin caused a significant inhibition of the development of hind paw oedema associated with adjuvant arthritis in rats and inhibited the increase in vascular permeability and the number of writhings induced by acetic acid in mice.5 Neo Actipone® Soap Nutshell, developed by Kaden Biochemicals, is a safe and mild extract from Sapindus mukorossi. Obtained from pure water extraction it is a 100% natural detergent. Neo Actipone Soap Nutshell is approved by ECOCERT SAS F 32600 according to the ECOCERT standards for natural and organic cosmetics. The extract is readily biodegradable (OECD 301B). Exhibiting an excellent cleaning performance Neo Actipone Soap Nutshell is a natural and mild alternative to synthetic surfactants.
References
1 Tanaka O., Tamura Y., Masuda H., Mizutani K. Application of Saponins in Foods and Cosmetics: Saponins of Mohave Yucca and Sapindus PPCC Mukorossi. Saponins used in Food and Agriculture, Waller and Yamasaki, Plenum Press, NY (1996). 2 Bergmann H. Saponine aus Sapindus mukorossi. Bayerische Julius-Maximilians-Universität, Würzburg, Lehrstuhl für Lebensmittelchemie, Prof. Dr. Peter Schreier (2006). 3 Nuhn P. Naturstoffchemie, Mikrobielle, pflanzliche und tierische Naturstoffe, 4. Auflage, S. Hirzel Verlag Stuttgart (2006). 4 Huang H.C., Liao S.C., Chang, F.R., Kuo Y.H., Wu Y.C. Molluscicidal Saponins from Sapindus mukorossi, Inhibitory Agents of Golden Apple Snails, Pomacea canaliculata. J. Agric. Food Chem. 51. 4916-4919 (2003). 5 Takagi K., Park E.H., Kato H. Anti-inflammatory Activities of Hederagenin and Crude Saponin isolated from Sapindus mukorossi GAERTN. Chem. Pharm. Bull. 28 (4). 1183-1188 (1980).
