72 JOURNAL OF COSMETIC SCIENCE
SOPHOROLIPIDS AND RHAMNOLIPIDS
The first generations of bio-based surfactants available for at least two decades were
obtained through chemical processes using sometimes problematic raw materials, which
limited their environmental friendliness. Most importantly, there were few, if any, bio-
based surfactants that could provide the cleansing and foaming properties of conventional
raw materials. These unmet market needs have been addressed by several players in the
chemical industry, but only a few have brought products to market in the quantities, quality,
and functionality required. These are the microbially-produced biosurfactants, a class of
surfactants that are not only based on renewable resources but also on environmentally
friendly, fermentation-based production technologies. Sophorolipids were the first available
biosurfactants at industrial quantities and are used, for example, in hand dishwashing
detergents and cosmetics. Recent technological breakthrough has enabled the large-scale
production of glycolipid-type biosurfactants, specifically rhamnolipids that show a unique
performance profile.1
Nature has developed biosurfactants through evolution, optimizing them to play a specific
role for the organisms which synthesize them therefore, a significant amount of process
optimization was required to develop an industrially viable production process. The sugar
used as a raw material for fermentation is usually dextrose syrup, obtained from maize. The
use of sugars from plant residues or other waste streams is also currently being investigated
for the production of biosurfactants, which offer further potential for improving the
overall sustainability profile. In contrast to bio-based surfactants, no tropical oils are used
for biosurfactants. In combination with their 100% biodegradability, biosurfactants are
therefore completely renewable, which is a strong argument in times in which circularity
is required. For every product manufactured today, it is important that its ingredients can
be broken down in nature and returned to the natural cycle.
Biodegradability of biosurfactants can be taken as given it is not the differentiating
feature compared to classic, fossil-based or bio-based surfactants. For more than 20 years,
biodegradability has rather been a legal requirement for surfactants used in detergents and
cleaning products in the EU. Biotechnology is also not an end in itself, and a sustainable
product alone is not enough, as the performance and cost-effectiveness of biosurfactants
must be at least equivalent to chemical counterparts. In this case, the biosurfactants must
compete with well-established molecules such as sodium lauryl (ether) sulphate (SLES, SLS)
or betaines, e.g. in terms of cleaning behavior, solubilization and foaming behavior, i.e.
typical and important performance characteristics of surfactants. However, it is essential
that biosurfactants do not simply perform the same as conventional surfactants, but that
a completely new type of product is offered—from the raw materials, the manufacturing
process, to attractive product properties, or even to new combinations of properties.
The necessary physicochemical properties typical of surfactants, such as surface activity,
micelle formation, or foaming of the glycolipids, are not sufficient to explain the special
property profile and predict suitability for certain applications. The real special feature of
glycolipid biosurfactants lies in the combination of application performance, in the case of
rhamnolipids for example excellent solubilization (e.g. in micellar water2), with exceptional
mildness towards a variety of biological and other materials (e.g. skin, proteins, aquatic
organisms, plastics, etc.).
In cases where the surfactant comes into contact with human skin, eyes, and mucous
membranes, the mildness of the formulation plays a crucial role. Ideally, the performance

73 Sophorolipids and Rhamnolipids
of the surfactant and its mildness should go hand in hand and not compromise each other.
The effect on skin can be evaluated using a variety of methods, including a patch test,
trans epidermal water loss, in which the glycolipids—in contrast to classic surfactants—
show basically no impairment of the skin barrier. Moreover, the glycolipids are too mild
for the red blood cell test, which has often been used in the past for correlation with eye
irritation: no lysis of the erythrocytes takes place under the experimental protocol, and
accordingly no denaturation of the released hemoglobin can be determined. The zein test is
also known for quantifying interaction with proteins. The maize protein zein is only water-
dispersible a reduction in turbidity is therefore a sign of denaturation, as the denatured
zein is more soluble in water than the native form. Glycolipids show hardly any interaction
with proteins as compared to standard surfactants such as sodium lauryl ether sulphate
or cocoamidopropyl betaine. This proves the superior behavior of glycolipids in terms of
mildness against proteins and enzymes, which is reasonable and to be expected, since due
to their natural origin from microorganisms a negative effect on enzymes and proteins
would be a disadvantage in evolution. The glycolipids are after all produced within the cell
by enzymes (=proteins).
Ultimately, the outstanding mildness of glycolipids is also reflected in their compatibility
with aquatic organisms. Rhamnolipids and sophorolipids show significantly better No
Observed Effect Concentration (NOEC) values for daphnia or algae compared to standard
surfactants. While the NOEC of classical surfactants is in the range of 10–20 mg/L, it is
200 mg/L for glycolplids, i.e. has no effect within the tested range, which confirms the
significantly lower effect on aquatic organisms and better biocompatibility.
This particular mildness of the glycolipids is surprising, as both rhamnolipids and
sophorolipids are anionic at application pH values, since they carry a carboxylate group. They
are therefore nominally soaps—but without the negative side effects of carboxylates and
other anionic surfactants, such as interaction with multivalent cations, polyquats, proteins,
and enzymes. The presence of the neighboring sugar group of the glycolipids thus seems to
limit the interaction possibilities of the carboxylate group. Accordingly, rhamnolipids and
sophorolipids are particularly insensitive to water hardness the “non-interaction” concerns
not only divalent cations but also polyquats, which allows an undisturbed deposition of
conditioning additives on hair. Similarly, rhamnolipids and sophorolipids do not lead to
stress corrosion cracking in plastics they are even able to counterbalance the negative
effects of fatty alcohol ethoxylates in cleaning formulations.
Foam formation is also an important performance parameter for cleaning solutions and
certain cosmetic applications. Consumers prefer products with good and long-lasting foam
formation in shampoos, shower/bath products, and hand dishwashing. Although foam is
not decisive for fat dissolving properties, it supports the sensory perception of cosmetic and
cleaning products and is a strong indicator of good cleaning performance for consumers.
The rhamnolipid combines the foaming properties of an anionic surfactant with the
mildness of a nonionic surfactant.
CONCLUSIONS
To conclude, in contrast to the cases where compromises had to be made when switching to
green and renewable products, glycolipids such as rhamnolipids offer an excellent technical,
sensory and sustainable alternative, with significant advantages in terms of mildness and