Back to basics: How formulators are using soapnut as a natural ingredient within hair care

Jennie Teague of James Robinson Speciality Ingredients discusses the use of soapnut extract as a natural surfactant and the role it plays in the journey towards a greener personal care market.

The trend towards natural ingredients within the personal care market is blossoming rapidly. Nature-derived surfactants in particular are becoming more desirable by both the formulator and the end user.

With consumers increasingly opting for more sustainable products, greater media coverage of the health benefits of natural ingredients and the demand for manufacturers to lower their environmental footprint, natural soapnut extract has quickly risen as one of the rising stars of the natural personal care market.

What is soapnut?

Formulators are often faced with the challenge of mimicking the aesthetics and performance characteristics of synthetic ingredients with natural alternatives. Customers might desire a specific colour or feel from a product that is sometimes difficult to achieve with plant-derived ingredients. However, the properties of soapnut extract, commonly known as Ritha, closely mimic those of synthetic ingredients.

Soapnut extract contains saponins, which are responsible for their foaming properties. They are extracted from the fruit of Sapindus mukurossi, belonging to the family Sapindaceae. Saponins are a large family of structurally related compounds of steroid or triterpenoid aglycone (sapogenin), linked to one or more oligosaccharide moieties by glycosidic linkage. The carbohydrate moiety consists of pentoses, hexoses or uronic acids.

The presence of both polar (sugar) and non-polar (steroid or triterpene) groups provides saponins with strong surface-active properties. Their physicochemical and biological properties feature structural diversity, which has led to a number of traditional and industrial applications. Many saponins exhibit distinct foaming properties and can be added to shampoos, liquid detergents, toothpaste and beverages as emulsifiers and long-lasting foaming agents.


Soapnut in personal care

Aqueous extraction is commonly used to produce soapnut extract, however, this type of extraction process results in a brown powder that can significantly affect the colour of finished formulations. By using alternative extraction techniques, it is possible to remove the high level of dark-coloured species present without reducing the level of water-soluble saponins. This will result in a soapnut powder with a much lower residual colour than aqueous extracted material.

The research team at James Robinson Speciality Ingredients has investigated the performance characteristics of soapnut extract in comparison to commonly used synthetic surfactants, sodium lauryl sulfate (SLS) and sodium laureth sulphate (SLES). The parameters used were pH, foam height, foam stability, mildness, detergency and volunteer performance comparisons.


Performance v. synthetics

When surfactants are applied to the skin, they interact with the skin’s structure, particularly with lipid and protein components, and may determine important skin toxicity at high concentrations.

The degree of skin damage by cleansing products depends on surfactant type, pH and product formulation. Our findings show that soapnut extract lies within the natural pH range of the skin, thus avoiding the irritation and dryness caused by alkaline surfactants, and making it a milder surfactant to incorporate in cleansing formulations.

Foam has an aesthetic utility in many detergent and personal care products. When comparing the foam height between 1% solutions of SLS, SLES and soapnut extract, we found that the properties of soapnut are comparable to those of synthetic foaming agents.

Foam stability is an important parameter in cleansing formulations, as the rate of weakening defines the stability of the foam. Foam with R50 values higher than 50% can be regarded as metastable. When comparing the R50 value of 1% solutions of soapnut extract, SLS and SLES, the soapnut extract displayed a foam stability of 92%, comparable to that of both SLS and SLES.

The degree of mildness of a surfactant-based product helps to indicate the level of potential irritation on the skin. Using the Zein solubility test method, an in vitro technique based on the solubilisation of water-insoluble corn protein, we discovered that SLS has an irritancy potential four times greater than natural soapnut extract.

The primary function of a surfactant is its detergency ability. This can be calculated by measuring sebum removal from the hair. Our tests revealed that 80% of sebum can be removed from the hair using a 1% solution of soapnut extract. While slightly lower than the level removed by SLS and SLES, this indicates that soapnut extract is an effective detergent.


Performance comparison

We asked ten volunteers to blind-test two shampoos formulations, one containing soapnut extract and one containing SLES and to evaluate and score the formulations for colour and odour, speed of foam, amount of foam, foam stability, usage feel, after-feel and overall liking.

The subjective opinions confirmed the data produced within the laboratory and show that the performance of soapnut to be comparable to synthetic surfactants. Overall, the volunteers preferred the formulation using soapnut extract.

Our studies demonstrate how soapnut extract is a comparable natural alternative to commonly used synthetic surfactants. It is mild in its application and has been shown to perform as effectively as both SLS and SLES.

The challenge now is to incorporate natural ingredients into the products that consumers use at an affordable price. When it comes to creating a greener planet, it is key that researchers have the support to find innovative, cost-effective, practical solutions to help us shift away from reliance on synthetic ingredients to more sustainable alternatives.