Abstract In this paper, the optimum conditions and kinetics of lipase-catalyzed transesterification reaction of nerol and vinyl acetate for the synthesis of neryl acetate were investigated in a solvent-free system. The optimum conditions were determined as follows: the reaction temperature was 40 °C, the amount of enzyme was 12 mg/mL, and there was no need to add water. Increasing the stirring speed to 200 r/min can eliminate the external diffusion limitations. There was no substrate inhibition when the substrate concentration was lower than 500 mmol/L. However, the experimental results indicated that the product inhibition effect should be considered. The results of the reaction kinetic analysis indicated that the reaction followed the ping-pong double-double reaction mechanism with product inhibition. Finally, the model parameters were calculated by MATLAB software and the results showed that the experimental values could be in good agreement with the simulated values, and the relative error was 6.98%.

Abstract In this paper, the lipase catalyzed transesterification of citronellol with vinyl acetate was investigated in ionic liquid. Firstly, six kinds of ionic liquids and six kinds of lipases from different sources were screened. The results showed that the lipase from Pseudomonas fluorescens had the best catalytic effect in the ionic liquid [bmimn][TF2]. The factors affecting the transesterification were optimized, and the optimal reaction conditions were as follows: the molar ratio of vinyl acetate to citronellol was 3:1; the reaction temperature was 40 °C; the amount of enzyme was 10 mg/mL; the rotating speed of the shaker was 200 r/min. When the concentration of substrate was below 500 mmol/L, no inhibition of substrate was found, while the inhibition of product was not negligible. The reuse of the lipase was studied, and the results showed that the catalytic activity of the lipase decreased by 20% after 7 times. The kinetic study showed that the reaction was a ping-pong bi-bi reaction mechanism with the inhibition of citronellyl acetate. The reaction kinetics model was established, and the parameters of the model were fitted by MATLAB software. The fitting values and the experimental values were in good agreement, and the relative error was only 7.75%.

Abstract Owing to the high content of lignocellulose, desiccated coconut become a healthy material for dietary fiber supplementation. In this study, the changes in solubility of the fibers of desiccated coconut were evaluated. The changes of the pHs and weight losses were studied. Furthermore, variations of the ingredient structures of desiccated coconut by hydrolysis by hydrochloric acid were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). After hydrolysis 30 s, the pHs of all systems increased, while six hours later, the pH of only system with initial pH = 1.00 decreased. The decline of pH only existed in hydrolysis systems with initial pH = 1.00, there is no relevant with the quantities of desiccated coconut. The lower initial pH of hydrolysis system was, the less the intrinsic viscosity of the desiccated coconut after hydrolysis was, the small the crystallinity was. After hydrolysis, the microstructure of the desiccated coconut become looser, and the secondary structure of the coconut protein became more stable and ordered. The results suggest that the hydrolysis of desiccated coconut mainly occurred in the branched chain and the non-crystalline region of lignocellulose, which transforms some insoluble dietary fiber into soluble dietary fiber. This improves the nutritional value of desiccated coconut.

Steady state properties of a kinetic model of Smolen- Baxter- Byrne [P. Smolen, D. A. Baxter, J. H. Byrne, Amer. J. Physiol. Cell. Physiol. 274, 531 (1998)] are investigated in presence of two time- correlated noises. The steady state probability distribution can be obtained by solving the Fokker- Planck equation. It is found that both the correlated- time between the white noise and the colored noise and that between the colored noises can convert the bistability to monostability while the former activates the transcription and the latter suppresses it.