(State Key Laboratory of Materials-Oriented Chemical Engineering,
School of Pharmaceutical Sciences, Nanjing Tech University, Nanjing,
China)
Abstract
Phytosterols usually have to be
esterified to various phytosterol esters to avoid their disadvantages of
unsatisfactory solubility and low bioavailability.
The enzymatic synthesis of
phytosterol esters in solvent-free system has advantages in terms of
environmental friendliness, sustainability, and selectivity. However,
the limitation of the low stability and recyclability of the lipase in
the solvent-free system, which often requires a relatively high
temperature to induce the viscosity, also increased the industrial
production cost. In this context, a low-cost material, namely diatomite,
was employed as the support in the immobilization of Candida
rugosa lipase (CRL) due to its multiple modification sites. The
Fe3O4 was also then introduced to this
system for quick and simple separation via the magnetic field. Moreover,
to further enhance the immobilization efficiency of
diatomite, a modification
strategy which involved the octadecyl and sulfonyl group for regulating
the hydrophobicity and interaction between the support and lipase was
successfully developed. The optimization of the ratio of the modifiers
suggested that the -SO3H/C18 (1:1.5)
performed best with an enzyme
loading and enzyme activity of 84.8 mg·g-1 and 54
U·g-1, respectively. Compared with free CRL, the
thermal and storage stability of CRL@OSMD was significantly improved,
which lays the foundation for the catalytic synthesis of phytosterol
esters in solvent-free systems. Fortunately, a yield of 95.0% was
achieved after optimizing the reaction conditions, and a yield of 70.0%
can still be maintained after 6 cycles.
Keywords: Candida
rugosa lipase, diatomite, octadecyl and sulfonyl modification,
immobilization, phytosterol esters