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This paper reports the lipase-catalyzed esterification of oleic acid (with ethanol) in a batch reactor at temperatures between 298 and 338 K using a wide range of the reactant ratio, β (0 < β < 2). All kinetic runs were performed under conditions of negligible transport limitations. The sigmoidal behavior evidenced from the initial rate-substrate concentration curve suggests the allosteric nature of the acrylic-supported Aspergillus lipase, and hence, the data were described by a non-Michaelis Menten kinetic model. The associated oleic acid binding coefficient and ethanol inhibition constant were obtained as 2.382 and 1.643 mmol L -1 , respectively. The allosteric effect was attributed to conformational change in the enzyme site occasioned by the presence of trace amounts of water formed within the first few minutes of the reaction. Indeed, the transient water concentration profile at different β values revealed an initial overshoot in water concentration before the relaxation to final equilibrium value after about 6 h. The appearance of the initial overshoot increased with decreasing β. The water concentration history is symptomatic of two first-order interacting processes fed by a self-propagating input consistent with the two-enzyme state concerted symmetry proposition for nonlinear feedback autoregulatory behavior. The rate-temperature envelope showed a maximum at about 318 K, suggesting protein denaturation above this temperature. Even so, a fit of the rate data obtained between 298 to 318 K gave an activation energy of 22.4 kJ mol -1 , typical of many enzymatic reactions. FTIR spectra of the catalysts displayed peaks at 1723.23 and 1666.12 cm -1 assigned to COOand NH 2 + groups, respectively, for both fresh and used specimens. BET measurements, however, revealed a significant drop in surface area between fresh (165 m 2 g -1 ) and used (5-20 m 2 g -1 ) catalysts. This was attributed to pore blockage of the immobilized enzyme by the relatively large oleic-acyl-lipase complex left after the reaction.

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Phytosterol from cocoa shell can be reused in food industries in order to add value of the agricultural waste. Its extraction from the cocoa shell using ethanol can be assisted by using microwave for effective heating. This study was carried out to delineate the effect of temperature, power and radiation time of the microwave onto the extraction of β-sitosterol, as the key phytosterol, from the cocoa shell of Theobroma cacao L. species using absolute ethanol. Salkowski test, IR spectra and GC-MS analyses confirmed the presence of β-sitosterol and a flame-ionization-detector gas chromatography was employed to measure its concentration. Based on the one-factor-at-a-time (OFAT) approach, the maximum yield was obtained 13% higher than the yield of conventional maceration, i.e. 3546.1 mg/100g, at the optimum values of 70°C, 500 W and 10 min. Solubility and boiling point of ethanol onto extraction at various extraction temperatures probably caused the differences.

The present study demonstrates the effect of light irradiation on the esterification of oleic acid catalyzed by immobilized Pseudomonas cepacia lipase. The reaction rates of all the experiments under light irradiation were found to be higher than dark conditions. The kinetics of reactions supported the Ping‐Pong Bi‐Bi mechanism with dead end inhibition by both the alcohol and acid substrates. Moreover, circular dichroism (CD) spectroscopy was used to analyze the effect of light on lipase enzyme. The CD spectroscopic studies confirmed that the conformational changes in the secondary structure of the lipase enzyme increased the reaction rate of light‐illuminated experiments, which might have opened up the active sites of enzymes and thus, resulted in higher reaction rates compared to dark reactions. These results have successfully demonstrated that the light illumination positively influenced the rate of P. cepacia enzyme‐catalyzed esterification reactions.