Microbial glycolipids are one of
the most interesting alternatives
to chemical-based surfactants as they exhibit improved biodegradability
and less toxicity. However, their potential has been limited because
of specificity of the yeast toward fatty acids having a carbon 16
or carbon 18 chain. This study focuses on sophorolipid (SL) production
by the yeast Starmerella bombicola using
myristic acid, a medium-chain carbon-14 fatty acid that has not been
used as a substrate for SL production. The production was optimized
for inoculum size and lipophilic substrate concentration. Furthermore,
we also studied the effect of medium-chain fatty acid on yeast cell
growth and optimized the process for excellent yield. The myristic
acid SL (MASL) so synthesized consisted of mono- and diacetylated
forms with preferential glycosylation at the methyl end group, as
determined by high-resolution mass spectrometry. Individual congeners
of the crude mixture were separated using dry column chromatography
and then structurally characterized by mass spectrometry. The synthesized
MASL was also shown to have promising surface tension, lowering abilities
with a low CMC of 14 mg/L. The SL derived from myristic acid exhibited
superior antibacterial activity as compared to SL derived from oleic
acid. MASL was also found to be more potent against Gram-positive
organisms as compared to Gram-negative organisms. This work, therefore,
demonstrates successful synthesis of myristic acid-derived SL and
its superior antibacterial activity, establishing a promising future
for this biosurfactant.
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