Microwave Irradiated Immobilized Lipase Catalyzed Synthesis of Alkyl Benzoate Esters by Transesterification: Mechanism and Kinetic Modeling

Process Intensification of Enzymatic Synthesis of Flavor Esters: A Review

The conventional flavor synthesis method suffers from low yields, time inefficiency, and extreme reaction conditions. Therefore, there is a necessity for the green and novel synthesis approach to overcome these limitations. The current review presents a holistic insight into different aspects associated with the synthesis of flavor esters using the immobilized enzyme. The application of process intensification tools such as ultrasound and microwave irradiation can enhance the reaction efficiency because of higher product recovery, less formation of by-products, and decreased energy consumption. This review presents the process intensification of value-added flavor esters synthesis and the mechanism of ultrasound and microwave action on the enzyme to enhance the enzyme activity and increase the reaction rate. It also summarizes the role of process intensification in enzymatic flavor ester synthesis, followed by specific examples as reported in the literature.

Process intensification using immobilized enzymes for the development of white biotechnology

Process intensification of biocatalysed reactions using different techniques such as microwaves, ultrasound, hydrodynamic cavitation, ionic liquids, microreactors and flow chemistry in various industries is critically analysed and future directions provided.

Chemoenzymatic Epoxidation of Limonene Using a Novel Surface-Functionalized Silica Catalyst Derived from Agricultural Waste

Limonene is one of the most important terpenes having wide applications in food and fragrance industries. The epoxide of limonene, limonene oxide, finds important applications as a versatile synthetic intermediate in the chemical industry. Therefore, attempts have been made to synthesize limonene oxide using eco-friendly processes because of stringent regulations on its production. In this regard, we have attempted to synthesize it using a cost-effective and eco-friendly process. Chemoenzymatic epoxidation of limonene to limonene oxide was carried out using in situ generation of peroxy octanoic acid from octanoic acid and H₂O₂. In this study, agricultural-waste rice husk ash (RHA)-derived silica was surface-functionalized using (3-aminopropyl) triethoxysilane (APTS), which was cross-linked using glutaraldehyde for immobilization of Candida antarctica lipase B. Furthermore, the immobilized enzyme was entrapped in calcium alginate beads to avoid enzyme leaching. Thus, limonene oxide was prepared using this catalyst under conventional and microwave heating. The microwave irradiation intensifies the process, reducing the reaction time under the same conditions. Maximum conversion of limonene to limonene oxide of 75.35 ± 0.98% was obtained in 2 h at 50 °C using a microwave power of 50 W. In the absence of microwave irradiation, the conventional heating gave 44.6 ± 1.14% conversion in 12 h. The reaction mechanism was studied using the Lineweaver-Burk plot, which follows a ternary complex mechanism with inhibition due to peroxyoctanoic acid (in other words H₂O₂). The prepared catalyst shows high reusability and operational stability up to four cycles.

Lipase activation by molecular bioimprinting: The role of interactions between fatty acids and enzyme active site

Bioimprinting is an easy, sustainable and low-cost technique that promotes a printing of potential substrates on enzyme structure, inducing a more selective and stable conformation. Bioimprinting promotes conformational changes in enzymes, resulting in better catalytic performance. In this work, the effect of bioimprinting of Burkholderia cepacia lipase (BCL) and porcine pancreatic extracts (PPE) with four different fatty acids (lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0), and stearic acid (C18:0)) was investigated. The results demonstrated that the better bioimprinting effect was in BCL with lauric acid in esterification reaction, promoting BCL activation in which relative enzyme activity was 70 times greater than nonimprinted BCL. Bioimprinting results were influenced by the carbon chain length of fatty acids imprinted in the BCL, in which the effects were weaker with the chain increase. Molecular docking was performed to better understand the bioimprinting method. The results of these simulations showed that indeed all fatty acids were imprinted in the active site of BCL. However, lauric acid presented the highest imprinting preference in the active site of BCL, resulting in the highest relative activity. Furthermore, Fourier transform infrared (FTIR) analysis confirmed important variations in secondary structure of bioimprinting BCL with lauric acid, in which there was a reduction in the α-helix content and an increase in the β-sheet content that facilitated substrate access to the active site of BCL and led higher rigidity, resulting in high activity. Bioimprinted BCL with lauric acid showed excellent operational stability in esterification reaction, maintaining its original relative activity after five successive cycles. Thus, the results show that bioimprinting of BCL with lauric acid is a successful strategy due to its high catalytic activity and reusability.

Microwave-Assisted Synthesis and Ionic Liquids: Green and Sustainable Alternatives toward Enzymatic Lipophilization of Anthocyanin Monoglucosides

Anthocyanins recycling and transformations into novel compounds have been of great interest of the scientific community to improve the circular economy and enhance their technological applications. The enzymatic acylation of anthocyanins into lipophilic derivatives by conjugation with fatty acids emerged as one of the approaches; however, the literature describes only the use of organic solvents and conventional heating. In this work, the production of cyanidin-3-glucoside-octanoic acid conjugate combining ionic liquids (ILs), microwave (MW) irradiation, and Candida antarctica lipase B as a biocatalyst was attempted for the first time. Overall, the use of MW irradiation could reduce drastically the reaction time, allowing the formation of an acylated product with similar concentrations to the conventional method. On the other hand, the study of the lipophilic conjugate synthesis using different ILs showed that their composition is crucial to achieve the desired enzymatic reaction, and in this case, the combination of an imidazolium derivative as the cation with the triflate as the anion was suitable for the production of this derivative. These promising results achieved through the combination of greener alternatives to those reported in the literature are a starting point for further developments to produce this kind of anthocyanin derivatives exploring such sustainable and ecofriendly conditions.

Novozym 40086 as a novel biocatalyst to improve benzyl cinnamate synthesis

Benzyl cinnamate is one of the derivatives of cinnamic acid, which can be used as the main constituent in perfume, UV filters and medicines. In this work, several commercial immobilized lipases (Novozym 40086, Novozym 435 and Lipozyme TLIM) and free lipases (lipase A and B from Candida sp., and lipozyme from Thermomyces linuginosous) were used as catalysts for benzyl cinnamate preparation by the esterification of benzyl alcohol with cinnamic acid. The effect of various esterification parameters (reaction time, reaction temperature, lipase concentration and substrate ratio) on benzyl cinnamate yield were also optimized and evaluated using response surface methodology (RSM). Among all tested lipases, Novozym 40086, as a new commercial immobilized lipase from Rhizomucor miehei immobilized on acrylic resin beads, showed the best activity for the esterification. Esterification parameters were optimized as follows: reaction temperature 46.3 °C, substrate molar ratio 1 : 3 (cinnamic acid/benzyl alcohol), Novozym 40086 concentration 23.1 mg mL-1, reaction time 11.3 h, and maximum benzyl cinnamate yield (96.2 ± 1.4%) were achieved under the optimal conditions. Novozym 40086 can be reused 9 times without significant decrease in benzyl cinnamate yield (90.1% yield after nine times). The activation energy for the Novozym 40086-catalyzed esterification was 14.96 ± 0.25 kJ mol-1. These results showed that Novozym 40086 was a novel and efficient biocatalyst for the esterification, which can be used as a good alternative for benzyl cinnamate production.

Synthesis of Geraniol Esters in a Continuous-Flow Packed-Bed Reactor of Immobilized Lipase: Optimization of Process Parameters and Kinetic Modeling

With increasing demand for perfumes, flavors, beverages, and pharmaceuticals, the various associated industries are resorting to different approaches to enhance yields of desired compounds. The use of fixed-bed biocatalytic reactors in some of the processes for making fine chemicals will be of great value because the reaction times could be reduced substantially as well as high conversion and yields obtained. In the current study, a continuous-flow packed-bed reactor of immobilized Candida antarctica lipase B (Novozym 435) was employed for synthesis of various geraniol esters. Optimization of process parameters such as biocatalyst screening, effect of solvent, mole ratio, temperature and acyl donors was studied in a continuous-flow packed-bed reactor. Maximum conversion of ~ 87% of geranyl propionate was achieved in 15 min residence time at 70 °C using geraniol and propionic acid with a 1:1 mol ratio. Novozym 435 was found to be the most active and stable biocatalyst among all tested. Ternary complex mechanism with propionic acid inhibition was found to fit the data.

Enzyme-catalyzed synthesis and kinetics of ultrasonic-assisted biodiesel production from waste tallow

The use of ultrasonic processing was evaluated for its ability to achieve adequate mixing while providing sufficient activation energy for the enzymatic transesterification of waste tallow. The effects of ultrasonic parameters (amplitude, cycle and pulse) and major reaction factors (molar ratio and enzyme concentration) on the reaction kinetics of biodiesel generation from waste tallow bio-catalyzed by immobilized lipase [Candida antarctica lipase B (CALB)] were investigated. Three sets of experiments namely A, B, and C were conducted. In experiment set A, two factors (ultrasonic amplitude and cycle) were investigated at three levels; in experiment set B, two factors (molar ratio and enzyme concentration) were examined at three levels; and in experiment set C, two factors (ultrasonic amplitude and reaction time) were investigated at five levels. A Ping Pong Bi Bi kinetic model approach was employed to study the effect of ultrasonic amplitude on the enzymatic transesterification. Kinetic constants of transesterification reaction were determined at different ultrasonic amplitudes (30%, 35%, 40%, 45%, and 50%) and enzyme concentrations (4, 6, and 8 wt.% of fat) at constant molar ratio (fat:methanol); 1:6, and ultrasonic cycle; 5 Hz. Optimal conditions for ultrasound-assisted biodiesel production from waste tallow were fat:methanol molar ratio, 1:4; catalyst level 6% (w/w of fat); reaction time, 20 min (30 times less than conventional batch processes); ultrasonic amplitude 40% at 5 Hz. The kinetic model results revealed interesting features of ultrasound assisted enzyme-catalyzed transesterification (as compared to conventional system): at ultrasonic amplitude 40%, the reaction activities within the system seemed to be steady after 20 min which means the reaction could proceed with or without ultrasonic mixing. Reversed phase high performance liquid chromatography indicated the biodiesel yield to be 85.6±0.08%.