Vol.:(0123456789) 1 3 Bioprocess and Biosystems Engineering https://doi.org/10.1007/s00449-018-1929-9 RESEARCH PAPER Kinetic and thermodynamic studies on the enzymatic synthesis of wax ester catalyzed by lipase immobilized on glutaraldehyde-activated rice husk particles Letícia C. D. Lima 1  · Daniela G. C. Peres 1  · Adriano A. Mendes 1 Received: 15 January 2018 / Accepted: 22 March 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Commercial lipase from Thermomyces lanuginosus has been immobilized on glutaraldehyde-activated rice husk particles via covalent attachment. It was reached maximum immobilized protein concentration of 27.5 ± 1.8 mg g −1 of dry support using the initial protein loading of 40 mg g −1 of support. The immobilized biocatalyst was used to synthesize cetyl oleate (wax ester) via direct esterifcation of oleic acid and cetyl alcohol. The infuence of relevant factors on ester synthesis, such as reaction temperature, biocatalyst concentration, presence or lack of hydrophobic organic solvents, acid:alcohol molar ratio, and reaction time has been evaluated. The experimental data were well ftted to a second-order reversible kinetic model to determine apparent kinetic constants. Thermodynamic studies have revealed that the reaction was a spontaneous and endothermic process. Under optimal experimental conditions, it was observed maximum ester conversion of 90.2 ± 0.6% in 9 h of reaction time in hexane medium using 1 M of each reactant (cetyl alcohol and oleic acid), at 50 °C and biocatalyst concentration of 15% m/v of reaction mixture. Similar conversion (91.5 ± 0.8%) in a solvent-free system was also obtained within 24 h of reaction. The biocatalyst retained 85% of its initial activity after 12 cycles within 9 h of reaction in hexane medium. The physicochemical properties of purifed ester have been determined in accordance with ASTM standards. The results indicate that the prepared biocatalyst has great potential for wax ester synthesis due to its satisfactory catalytic activ- ity and operational stability. Keywords Rice husk · Covalent attachment · Lipase · Wax ester synthesis · Kinetic/thermodynamic studies Introduction Wax esters are important organic compounds composed of long-chain alcohols and carboxylic acids which have been widely used in cosmetic, pharmaceutical, and lubri- cant industries. They can be extracted from animal and plant materials, such as honeycomb, jojoba and carnauba seeds, sperm whale, sheep wool, and seafowl feathers [1, 2]. However, natural wax esters are rare and very expensive for commercial exploitation. In this sense, synthetic esters from inexpensive renewable resources as vegetable oils, ani- mal fats, and their derivatives (free fatty acids) have been considered as promising substitutes to natural wax esters [1–7]. The production of synthetic wax esters has been per- formed by chemical or enzymatic routes [3]. The production of valuable organic compounds by enzymatic route is very attractive because it involves reactions under mild and envi- ronment friendly conditions [1–5, 7, 8, 10, 11]. The applica- tion of free enzymes (powder or soluble forms), including lipases, on an industrial scale is limited due to their difcult recovery from a given reaction system, which are gener- ally wasted on account of high susceptibility to inactivation by distorting their active conformation. Thus, techniques of immobilization on solid supports have been successfully proposed to overcome such drawbacks due to facilitating their reuse and purifcation of products. Moreover, enzyme immobilization can improve some important features as sta- bility, catalytic activity, and selectivity [7–11]. The present study deals with the enzymatic synthesis of an emollient ester used in cosmetic formulations (cetyl * Adriano A. Mendes adriano.mendes@unifal-mg.edu.br; adriano_amendes@yahoo.com.br 1 Institute of Chemistry, Federal University of Alfenas, Alfenas, MG 37130-001, Brazil