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
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
