Downstream processing of mannosylerythritol lipids produced by ...

Eur. J. Lipid Sci. Technol. 107 (2005) 373–380 Downstream MEL 377
facilitate the downstream process. As a result, all polymers
were able to accumulate MEL in different amounts
that could be eluted by MTBE or methanol. However, fatty
acids and soybean oil were also adsorbed. A specific
adsorption was not possible by the use of these resins.
Only a trend to higher adsorption capacity of MEL with
simultaneous decreasing accumulation of fatty acids and
soybean oil was observed in the order: XAD-16 . XAD-7
. XAD-4.
When the MEL-containing culture suspension was transferred
into a glass bottle, the separation of aggregated
MEL beads could be observed at the bottom as highly
viscous fluid (Fig. 4, left picture). This viscous MEL phase
and the MTBE extract of the whole culture suspension
(Fig. 3) possessed a similar composition (Fig. 4). After
sterilisation of the MEL-containing culture suspension at
121 7C for 20 min, two MEL-containing phases, a solid
sticky and an aqueous one, were formed, both fatty acid
enriched as well as soybean oil depleted (Fig. 4, right
picture). A small volume of a primary soybean oil-containing
top phase was also observed. Related to the total
mass of MEL (90 g L 21 ) yielded by MTBE extraction of the
culture suspension before heating, the MEL were distributed
after heating into the solid and aqueous phases by
89% and 11% (wt/vol), respectively. This solid phase was
easy to separate by pouring off the cell debris-containing
supernatant. If necessary, dependent on the intended
application of the MEL, the cell debris could be separated
by solving the solid phase in ethanol and subsequent filtration
using a pore width of 0.2 mm. About 11% (vol/vol)
of MEL remained suspended in the aqueous cell debris
phase and could additionally be recovered by extraction
with ethanol, centrifugation, rotary evaporation of the
solvent and vacuum drying.
Variations of time (1, 5, 15, 20 min) and temperature (100,
110, 115, 121 7C) of the culture suspension treatment
resulted in a nonessential difference of MEL content between
86.2–88.3% (wt-%) in the solid phase. Short incubation
times of 5 min led to the formation of a turbid
solid phase. The longer the time of treatment at each
temperature, the higher was the fatty acid and the lower
the soybean oil content, with a minimum of 0.3% (wt-%)
soybean oil and a maximum of 13.7% (wt-%) fatty acids
at 121 7C for 20 min (Fig. 4, grouped bars of solid phase).
Corresponding to Fig. 4, Fig. 5 shows HPLC and TLC
analyses of the MEL-containing phases before and after
heat treatment, as well as the distribution of the different
MEL. The maximum of 93% (wt-%) MEL transfer into the
solid phase with an appropriate reduction to 7% (wt-%)
MEL in the resulting aqueous phase was achieved at
110 7C for 10 min and was considered as the most effective
treatment for downstreaming the MEL. This solid
phase contained 88.3% (wt-%) MEL, 6.6% (wt-%) fatty
acids as well as 5.1% (wt-%) soybean oil and reduced the
surface tension of water/air to 31 mN m 21 (critical micelle
concentration 15 mg L 21 ).
Fig. 4. Composition of different MEL phases from a
culture suspension before (left) and after (right)
treatment at 121 7C for 20 min. The analyses were
carried out by HPLC.
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