Soy + Rhamnolipid Stability, Natural Soapnut and Sulfate-free: Foams in the Literature


Pre-COVID-19, globally, the market for foam-based beauty and personal care was projected to expand at a CAGR of 7% (US $1.18 billion) from 2020-2024, according to Technavio. The popularity of anti-pollution skin cleansing foams and adoption of organic products were recognized as drivers for this growth.

For example, the firm cites Chanel's Le Blanc intense brightening foam cleanser containing pearl extracts and glycine, which was designed to improve the appearance of dull skin, enhance radiance and boost hydration.

Now, amidst COVID-19, one might anticipate the spike in demand for cleansers to accelerate the growth of products in foam form. In relation, we offer this brief literature review of recent research to support the formulation of foams.

See related: Practical Foam Science

Soapnut for Natural Wetting, Antimicrobial Effects and Foam Stability

Panda, A., Kumar, A., Mishra, S. and Mohapatra, S.S.; Sustainable Chemistry and Pharmacy; available at:

A recent study published in Sustainable Chemistry and Pharmacy focused on the development of a natural surfactant derived from soapnut (Sapindus mukorossi). Researchers compared its efficacy and irritation potential with those of synthetic surfactants. Soapnut is a strong wetting agent and structurally free from the element or functional group contributing to toxicity. In addition, soapnut demonstrates antimicrobial properties and excellent foam stability.

See related: Is It Possible to Control Foam Collapse?

Critique of Alpha Sulfonates for Hair and Scalp Foam Formulas

Spryszyńska, K.; thesis paper; Base of Knowledge, Warsaw University of Technology; available at

This thesis paper sought to investigate the effect of disodium 2-sulfododecanoate on the foaming properties of standard and alternative surfactant systems. Results indicated it should neither be used as the primary surfactant in skin and hair cleansing products, nor be treated as a replacement for SLS and SLES. The sulfonate derivative showed poor rheological properties, although foaming properties were improved, to a limited extent.

Antimicrobial and Foamable Alcoholic Compositions

U.S. Patent Application 20200253198; assigned to: GOJO Industries, Inc.; publication date: Aug. 13, 2020 (accessed on Sept. 23, 2020)

According to GOJO inventors, alcoholic products are popular as sanitizers for the skin and aesthetics are important—users are more likely to use a product that is not sticky or slimy, and is not harsh on the skin. In relation, there is a need for new foaming surfactants that are able to form efficacious, stable and aesthetically pleasing foamable antimicrobial alcoholic compositions.

Described in this patent are antimicrobial and foamable alcoholic compositions. These comprise at least ~40% w/w of a C1-4 alcohol; and one or more silane surfactants selected from zwitterionic silane surfactants, or polyalkoxylated silane surfactants that contain at least one silane group and at least one polyalkylene oxide chain.

See related: How NOT to Formulate Hand Sanitizers

Sulfate-free Skin and Hair Care Foam Formulas

U.S. Patent Application 20200163846A1; assigned to: Procter & Gamble Co.; publication date: May 28, 2020 (accessed on Sept. 23, 2020)

As this P&G patent explains, personal care compositions such as shampoos typically use sulfate-based surfactants to generate high volume lather with good stability. However, some consumers prefer sulfate-free options. And while sulfate-free surfactants can be delivered via pump foam dispensers, formulas for foam delivery are more concentrated—and higher surfactant concentrations can lead to higher viscosity, which cannot be delivered through a typical pump foam dispenser. Or, if the composition is modified to lower the viscosity, it may not have enough lather to clean properly. 

There is thus a need for compositions that are substantially free of sulfate-based surfactants with low liquid phase viscosity that exhibit sufficient lather and acceptable foam quality. In response, disclosed herein is a composition that contains a surfactant system that is substantially free of sulfate-based surfactants, has a viscosity of less than 60 cP and a lather volume greater than 77 cm3.

Soy Protein + Rhamnolipids Stabilize Aqueous Foam

 Ruan, Q.-J., Wang, M.-P., Zou, Y., Lin, C., Cai, D.-C. and Wang, J.-M.; Industrial Crops and Products;

Research to be published in an upcoming issue of Industrial Crops and Products examines the influence of rhamnolipids (RHA) on the structure and foam characteristics of soy protein. Compared with pure protein, the foaming properties and foam stability were improved in the case of the soy protein-RHA complex. The authors propose the binding of RHA might facilitate the unfolding and adsorption of protein at the air-water interface, enhancing protein-protein interfacial interactions. This soy protein-RHA complex could be used as a natural foaming agent for body washes.

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