dc.description.abstract | Lipases are enzymes very well known for their laboratory and industrial application.
Various immobilization supports and techniques were examined in order to improve lipase
stability and activity for industrial application. Lipase can be immobilized by adsorption,
entrapment or by covalent binding [1]. Different supports are considered for enzyme
immobilization, organic or inorganic, natural or synthetic, but there is no unique solution.
Ideal support should posses enough active groups to interact with enzyme, but to be inert
to reaction media; it should be mechanically stable, renewable for many cycles and
inexpensive. Lately, nanoparticles of silica are used for enzyme immobilization because of
its extremely high surface area and controllable pore size. Nanoparticles of silica are
characterized by surface to volume ratio that is significantly higher than commonly used
supports. Some of the authors have also presented that nanoparticles of silica have
stabilization effect for the immobilized enzyme molecules[2]. Also in some cases
immobilization on nanoparticles also provides temperature stability of immobilized
enzyme[3].
In this study, nanoparticles of silica were modified in two-step process. The goal was to
introduce new reactive groups on silica surface, and make silica surface more suitable for
immobilization of lipase. In first step, nanoparticles of silica were treated with (3-
aminopropyl)-trimethoxysilane (APTMS), and then in step two, silica particles were treated
with cyanuric chloride (CTC) (temperature and molar ratio silica/CTC were variated). This
way nanoparticle of silica became rich in chloride groups, which enabled covalent
immobilization of lipase. FTIR analysis was performed after each modification step, and
confirmed presence of new active groups. Better results were obtained when second step
of modification was performed at 0 °C and high molar ratio silica/CTC. Lipase from
Candida rugosa was immobilized on modified nanoparticles of silica. Amount of proteins
bound was in range between 55 and 78%, but activity retention after immobilization
process was approximately 30%. Immobilized enzyme was used in reaction of aroma ester
synthesis, and reached conversion rate of 30% within 8 h. | sr |