Immobilization of Candida rugosa lipase on MSU-H type mesoporous silica for selective esterification of conjugated linoleic acid isomers with ethanol

•Adsorption of lipase on mesoporous silicas with different pore sizes was achieved.•The effect of adsorption conditions on immobilization of lipase was investigated.•The factors affecting conjugated linoleic acid (CLA) esterification were discussed.•The immobilized lipase remained total esterification (43.2–67.8%) in six times reuses.•c9, t11-CLA was esterified by the immobilized lipase faster than t10, c12-CLA.

Candida rugosa lipases (CRLs) immobilized on MSU-H type mesoporous silicas with different pore sizes (6.0, 7.2 and 13.3 nm) through physical adsorption and a cross-linking method were examined as biocatalysts for esterification of conjugated linoleic acid (CLA) isomers with ethanol in isooctane. N2 adsorption–desorption isotherms indicated that the MSU-H silicas and the immobilized CRL derivatives had mesoporous structure. Introduction of CRL molecules onto MSU-H was confirmed by Fourier transform infrared (FT-IR) spectra. The optimum conditions of the immobilization process (pH of CRL solution, 7.0; initial concentration of CRL solution, 1.6 mg/ml; contact time, 8–10 h) and the esterification reaction (temperature, 45 °C; molar ratio of CLA to ethanol, 1:1; biocatalyst, 6% by weight of CLA) were determined. The MSU-H material with pore size of 13.3 nm proved to be more suitable to immobilize CRL onto it than others. The CRL immobilized on MSU-H (pore size, 13.3 nm) by cross-linking gave a loading amount 48.2 mg CRL/g-dry support and a maximal hydrolytic activity of 3418.2 U/g-catalyst. It also exhibited high synthetic activity and operational stability and remained 43.2–67.8% of total esterification in 48 h consecutive six runs under the optimized reaction conditions. Moreover, the immobilized CRLs catalyzed 2.0–3.1 times of esterification of cis-(c)9, trans-(t)11-CLA faster than that t10, c12-CLA. The formation of ethyl esters of CLA isomers was identified by GC–MS analysis.

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