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Micelle size characterization of lipopeptides produced by B. subtilis and their recovery by the two-step ultrafiltration process
The aim of this work was to investigate the lipopeptides aggregation behavior in single and mixed solutions
in a wide range of concentrations, in order to optimize their separation and purification following
the two-step ultrafiltration process and using large pore size membranes (up to MWCO = 300 kDa).
Micelle size was determined by dynamic light scattering. In single solutions of lipopeptide both surfactin
and mycosubtilin formed micelles of different size depending on their concentration, micelles of average
diameter = 5–105 nm for surfactin and 8–18 nm for mycosubtilin. However when the lipopeptides were
in the same solution they formed mixed micelles of different size (d = 8 nm) and probably conformation
to that formed by the individual lipopeptide, this prevents their separation according to size. These lipopeptides
were purified from fermentation culture by the two-step ultrafiltration process using different
MWCO membranes ranging from 10 to 300 kDa. This led to their effective rejection in the first ultrafiltration
step by membranes with MCWO = 10–100 kDa but poor rejection by the 300 KDa membrane. The
lipopeptides were recovered at 90% purity (in relation to protein) and with 2.34 enrichment in the permeate
of the second ultrafiltration step with the 100 KDa membrane upon addition of 75% ethanol