Enzyme immobilisation technology is an effective means to improve sugar ester production through the employment of biocatalysts. In the present study, immobilisation of Candida rugosa (CRL) lipase onto amino-activated mica is performed via covalent bonding (namely Amino-CRL) and the cross-linking of lipases into nano-reactors through physical adsorption (namely NER-CRL). Free and immobilised lipases were tested for their esterification activities. Specific activities for Amino-CRL and NER-CRL increased by 2.4 and 2.6-fold, respectively, upon immobilisation. Extending this work, immobilised lipases have novel capabilities in the synthesis of sugar esters. The optimised conditions for sugar fatty acid ester syntheses are 48 h at 2:1 of molar ratio of lactose sugar to capric acid at 55 �C. Furthermore, a high operational stability with half-lives of over 13 and 10 runs was achieved for NER-CRL and Amino-CRL, respectively, indicating the efficiency of the immobilisation process. � 2011 Elsevier Ltd. All rights reserved.

The utilization of natural mica as a biocatalyst support in kinetic investigations is first described in this study. The formation of lactose caprate from lactose sugar and capric acid, using free lipase (free-CRL) and lipase immobilized on nanoporous mica (NER-CRL) as a biocatalyst, was evaluated through a kinetic study. The apparent kinetic parameters, Km and Vmax, were determined by means of the Michaelis-Menten kinetic model. The Ping-Pong Bi-Bi mechanism with single substrate inhibition was adopted as it best explains the experimental findings. The kinetic results show lower Km values with NER-CRL than with free-CRL, indicating the higher affinity of NER-CRL towards both substrates at the maximum reaction velocity (Vmax,app > Vmax). The kinetic parameters deduced from this model were used to simulate reaction rate data which were in close agreement with the experimental values.

Mica was modified either by acid treatment, grafting with aminopropyl-, octyl-, vinyl-, mercapto- and glycidoxy-triethoxysilanes, and activation of pre-treated support with glutaraldehyde (Glu). The derivatives were characterized by X-ray diffraction (XRD), infra-red spectroscopy (FTIR), surface area and porosity analysis, scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM) techniques. The modified micas were used for immobilization of lipase from Candida rugosa (CRL). Activity of the lipase was determined by esterification and exhibited the improved activity than the free enzyme following the order; Amino-CRL > Glu-Amino-CRL > Octyl-CRL > Vinyl-CRL > Glycidoxy-CRL > Mercapto-CRL > Mica-CRL. Lipase immobilized mica showed enhanced protein loading (up to 8.22 mg protein/g support) and immobilization (up to 78%) compared to the free lipase and unmodified mica. � 2009 Elsevier B.V. All rights reserved.