Ultrasound-assisted lipase-catalyzed transesterification of soybean oil in organic solvent system

Hydrolysis of macauba kernel oil: ultrasound application in the substrates pre-emulsion step and effect of the process variables

The main goal of the present work was to evaluate the application of ultrasound as a previous step to promote the substrates pre-emulsion in the hydrolysis reaction of macauba kernel oil (MKO). The ultrasound effect on the substrates pre-emulsion was evaluated on the free fatty acid (FFA) content, as well as the process variables (reaction time, percentage of catalyst Lipozyme® RM IM, and buffer solution). Reactions carried out with the substrates pre-emulsion presented higher FFA production, up to a 40 wt% increase in 1 hour of reaction, yielding 80 wt% of FFAs in 8 hours. The use of catalyst in the reaction medium, from 5 to 15 wt%, favored the FFAs production in 2 hours of reaction. Addition of 25 to 100 wt% of buffer solution led to 86 wt% of FFAs in 4 hours of reaction. Enzyme recycling resulted in a slight decrease in the FFA content, although the catalyst had maintained 85% of its initial activity after 30 h of use. Therefore, the ultrasound pre-emulsion previous step allowed a more efficient hydrolysis reaction of MKO, leading to an increase of up to 40 wt% on the FFA content, when compared to the hydrolysis without such step.

Current State and Perspectives on Transesterification of Triglycerides for Biodiesel Production

Triglycerides are the main constituents of lipids, which are the fatty acids of glycerol. Natural organic triglycerides (viz. virgin vegetable oils, recycled cooking oils, and animal fats) are the main sources for biodiesel production. Biodiesel (mono alkyl esters) is the most attractive alternative fuel to diesel, with numerous environmental advantages over petroleum-based fuel. The most practicable method for converting triglycerides to biodiesel with viscosities comparable to diesel fuel is transesterification. Previous research has proven that biodiesel–diesel blends can operate the compression ignition engine without the need for significant modifications. However, the commercialization of biodiesel is still limited due to the high cost of production. In this sense, the transesterification route is a crucial factor in determining the total cost of biodiesel production. Homogenous base-catalyzed transesterification, industrially, is the conventional method to produce biodiesel. However, this method suffers from limitations both environmentally and economically. Although there are review articles on transesterification, most of them focus on a specific type of transesterification process and hence do not provide a comprehensive picture. This paper reviews the latest progress in research on all facets of transesterification technology from reports published by highly-rated scientific journals in the last two decades. The review focuses on the suggested modifications to the conventional method and the most promising innovative technologies. The potentiality of each technology to produce biodiesel from low-quality feedstock is also discussed.

Shallot skin profilling, computational evaluation of physicochemical properties, ADMET, and molecular docking of its components against P2Y12 receptor

OBJECTIVES

Medicinal plants are a source of many compounds that are useful in the pharmaceutical field for novel drug development. Polyphenols and the flavonoid group in plants are known to have several activities, such as relieving cardio vascular disease (CVD). The outer skin of the shallot which is disposed of as waste is known to have an antiplatelet activity which was tested in vitro assay. To date, there is no study reported on the ADMET profile and physicochemical properties of the active component of the shallot skins.

METHODS

The extraction of shallot skins was conducted by ultrasonic irradiation using ethanol. The phytochemical screenings were carried out by TLC and color reaction. The profiling of its active ingredient was presented by GC-MS, HPLC and spectrophotometry UV-vis. Whereas their physicochemical properties were analyzed by ChemDraw 17.00 program and the ADMET predictions were studied using pkCSM online tool. The MVD program was operated in the docking study on protein P2Y12 (PDB ID 4PXZ).

RESULTS

The extract showed the presence of polyphenol, flavonoids, quercetin, natalensine-3,5-dinitrobenzoate; bis[2-(2-fluorophenyl)-6-fluoroquinolin-4-yl]amine, benzo[a]heptalene, N-(trifluoroacetyl) methyl-N-deacethyl-colchicine. The ADMET prediction data displayed that the compounds in the extract have good absorption so that they can be used in the oral and transdermal routes. Some components in the extract have lower MDS than clopidogrel.

CONCLUSIONS

The ultrasonicated shallot skin extract can be used as additional resources of the active pharmaceutical ingredients and to have the potency to be developed as an oral or transdermal preparation.

Ultrasound-assisted production of biodiesel using engineered methanol tolerant Proteus vulgaris lipase immobilized on functionalized polysulfone beads

In the present study, Proteus vulgaris lipase (PVL) was engineered using directed evolution to increase methanol tolerance so that it would be more tolerant and efficient for harsh conditions employed in biodiesel synthesis, which is limiting their industrial use. The influence of ultrasound under different experimental conditions on the biodiesel conversion yield using methanolysis of non-edible neem oil was also emphasized. A special attention was also paid to the immobilization of lipase on Polysulfone (PS) beads and comparative studies with industrially used Burkholderia cepacia lipase. The Engineered Proteus vulgaris lipase showed >80% activity after 3 h when incubated in 50% methanol with simultaneous sonication. The lipase retained improved longevity (~70% residual activity) over wild-type PVL over repeated use.

Ultrasound-Assisted Esterification of Valeric Acid to Alkyl Valerates Promoted by Biosilicified Lipases

A novel, environmentally friendly, and sustainable ultrasound-assisted methodology in the valorization of valeric acid to alkyl valerate using a biosilicified lipase from Candida antarctica is reported. This one-pot room temperature methodology of enzyme biosilicification leads to biosilicified lipases with improved activity and reaction efficiency as compared to free enzymes. Yields in the ultrasound-promoted esterification of valeric acid was ca. 90% in 2 h with 15% m/v of biosilicified lipase (Bio-lipase; 616 U/g _biocatalyst enzymatic activity) and a molar ratio 1:2 (valeric acid:ethanol), slightly superior to that observed by the free enzyme (75% conversion, 583U/g _biocatalyst enzymatic activity). The reuse of enzymes in these conditions was tested and the results show a relatively good reusability of these biosilicified enzymes under the investigated conditions, particularly preserving fairly stable specific activities (616 vs. 430 U/g _biocatalyst after four reuses).

Synthesis of 2-docosahexaenoylglycerol by enzymatic ethanolysis

Synthesis of 2-docosahexaenoylglycerol with high nutritional value was conducted by enzymatic ethanolysis of algal oil. The effects of lipase type, substrate molar ratio of algal oil to ethanol, reaction time, reaction temperature and lipase load on the content of 2-monoacylglycerols (2-MAGs) in the crude product were investigated. Under the optimal conditions, 27-31% 2-MAGs were obtained in the ethanolysis reaction. Lipozyme 435 exhibited 1,3-specific selectivity and maintained stable operational stability after 7 successive reuse cycles. The enzymatic ethanolysis catalyzed by Lipozyme 435 could both synthesize 2-MAGs and concentrate DHA. Further purification of 2-MAGs was performed with solvent extraction by 85% ethanol aqueous solution and hexane, obtaining 95% 2-MAGs in a yield of 67%. The contents of DHA in 2-MAGs product and 2-MAGs fraction were 74.76% and 75.66%, respectively, which were about 26% higher than that in the algal oil. Therefore, this method is efficient and environmental-friendly for synthesis of 2-docosahexaenoylgylcerol.

Microalgae as feedstock for biodiesel production under ultrasound treatment - A review

The application of ultrasound in biodiesel production has recently emerged as a novel technology. Ultrasound treatment enhances the mass transfer characteristics leading to the increased reaction rate with short reaction time and potentially reduces the production cost. In this review, application of ultrasound-assisted biodiesel production using acid, base and enzyme catalysts is presented. A critical assessment of the current status of ultrasound in biodiesel production was discussed with the emphasis on using ultrasound for efficient microalgae biodiesel production. The ultrasound in the biodiesel production enhances the emulsification of immiscible liquid reactant by microturbulence generated by cavitation bubbles. The major benefit of the ultrasound-assisted biodiesel production is a reduction in reaction time. Several different methods have been discussed to improve the biodiesel production. Overall, this review focuses on the current understanding of the application of ultrasound in biodiesel production from microalgae and to provide insights into future developments.

Ultrasound-assisted improvements in biocatalytic activity and production of organic-solvent stable protease from Bacillus circulans MTCC 7942

This study reports the ultrasound-assisted improvements in biocatalytic activity and production of protease from organic solvent-tolerant, alkaliphilic Bacillus circulans MTCC 7942. The strain withstands 10min ultrasound treatment (33kHz); this treatment promotes the growth of bacterium. The protease production was improved by 1.5-fold on multiple ultrasound treatment at 0, 6, 12h intervals. Although the substrate casein remains unaffected by ultrasound treatment (33kHz, 10min); the treatment had boosted the enzyme activity of purified protease. Also, the ultrasound treated purified protease showed enhancement in enzyme activity in presence of n-dodecane, n-octane, n-hexadecane, n-decane, xylene, butanol, toluene, pyridine and chloroform.

An Efficient Approach for Lipase-Catalyzed Synthesis of Retinyl Laurate Nutraceutical by Combining Ultrasound Assistance and Artificial Neural Network Optimization

Although retinol is an important nutrient, retinol is highly sensitive to oxidation. At present, some ester forms of retinol are generally used in nutritional supplements because of its stability and bioavailability. However, such esters are commonly synthesized by chemical procedures which are harmful to the environment. Thus, this study utilized a green method using lipase as a catalyst with sonication assistance to produce a retinol derivative named retinyl laurate. Moreover, the process was optimized by an artificial neural network (ANN). First, a three-level-four-factor central composite design (CCD) was employed to design 27 experiments, which the highest relative conversion was 82.64%. Further, the optimal architecture of the CCD-employing ANN was developed, including the learning Levenberg-Marquardt algorithm, the transfer function (hyperbolic tangent), iterations (10,000), and the nodes of the hidden layer (6). The best performance of the ANN was evaluated by the root mean squared error (RMSE) and the coefficient of determination (R²) from predicting and observed data, which displayed a good data-fitting property. Finally, the process performed with optimal parameters actually obtained a relative conversion of 88.31% without long-term reactions, and the lipase showed great reusability for biosynthesis. Thus, this study utilizes green technology to efficiently produce retinyl laurate, and the bioprocess is well established by ANN-mediated modeling and optimization.

An investigation of lipase catalysed sonochemical synthesis: A review

Ultrasonic irradiation has recently gained attention of researchers for its process intensification in numerous reactions. Earlier ultrasound was known for its application either to deactivate enzyme activity or to disrupt the cell. However, in recent years, practice of ultrasonic irradiation began to emerge as a tool for the activation of the enzymes under mild frequency conditions. The incorporation of ultrasound in any of enzymatic reactions not only increases yield but also accelerates the rate of reaction in the presence of mild conditions with better yield and less side-products. To attain maximum yield, it is crucial to understand the mechanism and effect of sonication on reaction especially for the lipase enzyme. Thus, the influence of ultrasound irradiation on reaction yield for different parameters including temperature, enzyme concentration, mole ratio of substrates, solvents ultrasonic frequency and power was reviewed and discussed. The physical effect of cavitation determined by bubble dynamics and rate of reaction through kinetic modelling also needs to be assessed for complete investigation and scale up of synthesis. Thus, prudish utilisation of ultrasound for enzymatic synthesis can serve better future for sustainable and green chemistry.

Ultrasonic enhancement of lipase-catalysed transesterification for biodiesel synthesis

The production of biodiesel was carried out from canola oil and methanol catalysed by lipase from Candida rugosa under different ultrasonic experimental conditions using horn (20kHz) and plate (22, 44, 98 and 300kHz) transducers. The effects of experimental conditions such as horn tip diameter, ultrasonic power, ultrasonic frequency and enzyme concentrations on biodiesel yield were investigated. The results showed that the application of ultrasound decreased the reaction time from 22-24h to 1.5h with the use of 3.5cm ultrasonic horn, an applied power of 40W, methanol to oil molar ratio of 5:1 and enzyme concentration of 0.23wt/wt% of oil. Low intensity ultrasound is efficient and a promising tool for the enzyme catalysed biodiesel synthesis as higher intensities tend to inactivate the enzyme and reduce its efficiency.

X-Ray Crystallography as a Tool to Determine Three-Dimensional Structures of Commercial Enzymes Subjected to Treatment in Pressurized Fluids

The study of enzyme function often involves a multi-disciplinary approach. Several techniques are documented in the literature towards determining secondary and tertiary structures of enzymes, and X-ray crystallography is the most explored technique for obtaining three-dimensional structures of proteins. Knowledge of three-dimensional structures is essential to understand reaction mechanisms at the atomic level. Additionally, structures can be used to modulate or improve functional activity of enzymes by the production of small molecules that act as substrates/cofactors or by engineering selected mutants with enhanced biological activity. This paper presentes a short overview on how to streamline sample preparation for crystallographic studies of treated enzymes. We additionally revise recent developments on the effects of pressurized fluid treatment on activity and stability of commercial enzymes. Future directions and perspectives on the the role of crystallography as a tool to access the molecular mechanisms underlying enzymatic activity modulation upon treatment in pressurized fluids are also addressed.

Ultrasound assisted enzyme catalyzed hydrolysis of waste cooking oil under solvent free condition

The present work demonstrates the hydrolysis of waste cooking oil (WCO) under solvent free condition using commercial available immobilized lipase (Novozyme 435) under the influence of ultrasound irradiation. The process parameters were optimized using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound intensity. It has been observed that ultrasound-assisted lipase-catalyzed hydrolysis of WCO would be a promising alternative for conventional methods. A maximum conversion of 75.19% was obtained at mild operating parameters: molar ratio of oil to water (buffer pH 7) 3:1, catalyst loading of 1.25% (w/w), lower ultrasound power 100W (ultrasound intensity - 7356.68Wm(-2)), duty cycle 50% and temperature (50°C) in a relatively short reaction time (2h). The activation energy and thermodynamic study shows that the hydrolysis reaction is more feasible when ultrasound is combined with mechanical agitation as compared with the ultrasound alone and simple conventional stirring technique. Application of ultrasound considerably reduced the reaction time as compared to conventional reaction. The successive use of the catalyst for repetitive cycles under the optimum experimental conditions resulted in a loss of enzymatic activity and also minimized the product conversion.

Ultrasound intensification suppresses the need of methanol excess during the biodiesel production with Lipozyme TL-IM

The synthesis of biodiesel from sunflower oil and methanol based on transesterification using the immobilized lipase from Thermomyces lanuginosus (Lipozyme TL-IM) has been investigated under silent conditions and under an ultrasound field. Ultrasound assisted process led to reduced processing time and requirement of lower enzyme dosage. We found for the first time that oil to methanol ratio of 1:3 was favored for the ultrasound assisted enzymatic process which is lower than that observed for the case of conventional stirring based approach (ratio of 1.4). Our results indicate that intensification provided by ultrasound suppresses the need of the excess of the methanol reactant during the enzymatic biodiesel production. Ultrasound assisted enzymatic biodiesel production is therefore a faster and a cleaner processes.

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%.

Production and characterization of biodiesel using nonedible castor oil by immobilized lipase from Bacillus aerius

A novel thermotolerant lipase from Bacillus aerius was immobilized on inexpensive silica gel matrix. The immobilized lipase was used for the synthesis of biodiesel using castor oil as a substrate in a solvent free system at 55°C under shaking in a chemical reactor. Several crucial parameters affecting biodiesel yield such as incubation time, temperature, substrate molar ratio, and amount of lipase were optimized. Under the optimized conditions, the highest biodiesel yield was up to 78.13%. The characterization of synthesized biodiesel was done through FTIR spectroscopy, ¹H NMR spectra, and gas chromatography.

Immobilization of Pseudomonas fluorescens lipase on hydrophobic supports and application in biodiesel synthesis by transesterification of vegetable oils in solvent-free systems

This work describes the preparation of biocatalysts for ethanolysis of soybean and babassu oils in solvent-free systems. Polystyrene, Amberlite (XAD-7HP), and octyl-silica were tested as supports for the immobilization of Pseudomonas fluorescens lipase (PFL). The use of octyl-silica resulted in a biocatalyst with high values of hydrolytic activity (650.0 ± 15.5 IU/g), immobilization yield (91.3 ± 0.3 %), and recovered activity (82.1 ± 1.5 %). PFL immobilized on octyl-silica was around 12-fold more stable than soluble PFL, at 45 °C and pH 8.0, in the presence of ethanol at 36 % (v/v). The biocatalyst provided high vegetable oil transesterification yields of around 97.5 % after 24 h of reaction using babassu oil and around 80 % after 48 h of reaction using soybean oil. The PFL-octyl-silica biocatalyst retained around 90 % of its initial activity after five cycles of transesterification of soybean oil. Octyl-silica is a promising support that can be used to immobilize PFL for subsequent application in biodiesel synthesis.

The combined use of ultrasound and molecular sieves improves the synthesis of ethyl butyrate catalyzed by immobilized Thermomyces lanuginosus lipase

In this work, the combined use of ultrasound energy and molecular sieves was investigated for the synthesis of ethyl butyrate, ester with mango and banana notes, catalyzed by the immobilized lipase from Thermomyces lanuginosus (Lipozyme TL-IM). Initially, the best concentrations of biocatalysts (35%) and butyric acid (0.7M) were tested using ultrasound as an alternative to mechanical agitation. The amount of acid in the reaction could be increased by 2-fold when compared to previous works where mechanical agitation was used. In the next step, substrate molar ratio and reaction temperature were optimized and the best conditions were at their lowest levels: 1:1 (acid:alcohol), and 30°C, reaching 61% of conversion in 6h. Molecular sieves (3Å) were added to optimized reaction medium in order to remove the formed water and improve the maximum yield. The reaction yield increased 1.5 times, reaching 90% of conversion in 6h, when 60mg of molecular sieves per mmol of butyric acid was used. Finally, the reuse of Lipozyme TL-IM for the ultrasound-assisted synthesis of ethyl butyrate was verified for 10 batches, without any appreciable loss of activity, whereas in systems using mechanical agitation, the biocatalyst was completely inactivated after 5 batches. These results suggest that the combined use of ultrasound and molecular sieves greatly improve esterification reactions by stabilizing the enzyme and increasing yields.

Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate

The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100W), duty cycle 50% and temperature (60°C) in a relatively short reaction time (4h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4h as compared to conventional stirring method (14h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion.

Combined effects of ultrasound and immobilization protocol on butyl acetate synthesis catalyzed by CALB

It is well established that the performance of lipase B from Candidaantarctica (CALB) as catalyst for esterification reactions may be improved by the use of ultrasound technology or by its immobilization on styrene-divinylbenzene beads (MCI-CALB). The present research evaluated the synthesis of butyl acetate using MCI-CALB under ultrasonic energy, comparing the results against those obtained using the commercial preparation, Novozym 435. The optimal conditions were determined using response surface methodology (RSM) evaluating the following parameters: reaction temperature, substrate molar ratio, amount of biocatalyst, and added water. The optimal conditions for butyl acetate synthesis catalyzed by MCI-CALB were: temperature, 48.8 °C; substrate molar ratio, 3.46:1 alcohol:acid; amount of biocatalyst, 7.5%; and added water 0.28%, both as substrate mass. Under these conditions, 90% of conversion was reached in 1.5 h. In terms of operational stability, MCI-CALB was reused in seven cycles while keeping 70% of its initial activity under ultrasonic energy. The support pore size and resistance are key points for the enzyme activity and stability under mechanical stirring. The use of ultrasound improved both activity and stability because of better homogeneity and reduced mechanical stress to the immobilized system.

Ultrasound assisted enzymatic conversion of non edible oil to methyl esters

Conventional and ultrasound-assisted hydrolysis and subsequent esterification of Nagchampa oil under mild operating conditions have been investigated with an objective of intensification of methyl esters production using a sustainable approach. The effect of ratio of reactants, temperature, enzyme loading, pretreatment of enzyme (using ultrasonic irradiations) on the hydrolysis and esterification reaction has been studied. Optimum conditions for hydrolysis were observed to be 1:1 weight ratio of oil: water for Lip Z and 1:3 for Lip 2 enzymes, enzyme loading of 400 units for Lip Z and 800 mg for Lip 2 enzymes and reaction time of 6h. In the case of esterification reaction, optimum conditions obtained were oil to methanol molar ratio of 1:2, enzyme loading of 1000 mg and reaction time of 20 h. Use of pretreated enzyme (using ultrasonic irradiations) was found to increase the extent of esterification reaction from 75% to 92.5%. It was observed that use of ultrasound in the reaction significantly intensified the esterification reaction with time requirement reducing from 20 h for conventional stirring based approach to only about 7.5 h in the presence of ultrasound. The extent of esterification obtained with sonicated enzyme also increased to 96% from 75% with unsonicated enzyme.

A review on lipase-catalyzed reactions in ultrasound-assisted systems

The named "green chemistry" has been receiving increasing prominence due to its environmentally friendly characteristics. The use of enzymes as catalysts in processes of synthesis to replace the traditional use of chemical catalysts present as main advantage the fact of following the principles of the green chemistry. However, processes of enzymatic nature generally provide lower yields when compared to the conventional chemical processes. Therefore, in the last years, the ultrasound has been extensively used in enzymatic processes, such as the production of esters with desirable characteristics for the pharmaceutical, cosmetics, and food industry, for the hydrolysis and glycerolysis of vegetable oils, production of biodiesel, etc. Several works found in the open literature suggest that the energy released by the ultrasound during the cavitation phenomena can be used to enhance mass transfer (substrate/enzyme), hence increasing the rate of products formation, and also contributing to enhance the enzyme catalytic activity. Furthermore, the ultrasound is considered a "green" technology due to its high efficiency, low instrumental requirement and significant reduction of the processing time in comparison to other techniques. The main goal of this review was to summarize studies available to date regarding the application of ultrasound in enzyme-catalyzed esterification, hydrolysis, glycerolysis and transesterification reactions.

Ultrasound-assisted butyl acetate synthesis catalyzed by Novozym 435: enhanced activity and operational stability

The influence of low-frequency ultrasound (40 kHz) in the esterification reaction between acetic acid and butanol for flavor ester synthesis catalyzed by the commercial immobilized lipase B from Candida antarctica (Novozym 435) was evaluated. A central composite design and the response surface methodology were used to analyze the effects of the reaction parameters (temperature, substrate molar ratio, enzyme content and added water) and their response (yields of conversion in 2.5 h of reaction). The reaction was carried out using n-hexane as solvent. The optimal conditions for ultrasound-assisted butyl acetate synthesis were found to be: temperature of 46 °C; substrate molar ratio of 3.6:1 butanol:acetic acid; enzyme content of 7%; added water of 0.25%, conditions that are slightly different from those found using mechanical mixing. Over 94% of conversion was obtained in 2.5h under these conditions. The optimal acid concentration for the reaction was determined to be 2.0 M, compared to 0.3 M without ultrasound treatment. Enzyme productivity was significantly improved to around 7.5-fold for each batch when comparing ultrasound and standard mechanical agitation. The biocatalyst could be directly reused for 14 reactions cycles keeping around 70% of its original activity, while activity was virtually zeroed in the third cycle using the standard mixing system. Thus, compared to the traditional mechanical agitation, ultrasound technology not only improves the process productivity, but also enhances enzyme recycling and stability in the presence of acetic acid, being a powerful tool to improve biocatalyst performance in this type of reaction.

Hybrid response surface methodology-genetic algorithm optimization of ultrasound-assisted transesterification of waste oil catalysed by immobilized lipase on mesoporous silica/iron oxide magnetic core-shell nanoparticles

The production ofbiodiesel by transesterification of waste cooking oil (WCO) to partially substitute petroleum diesel is one of the measures for solving the twin problems of environment pollution and energy demand. An environmentally benign process for the enzymatic transesterification using immobilized lipase has attracted considerable attention for biodiesel production. Here, a superparamagnetic, high surface area substrate for lipase immobilization is evaluated. These immobilization substrates are composed of mesoporous silica/superparamagnetic iron oxide core-shell nanoparticles. The effects of methanol ratio to WCO, lipase concentration, water content and reaction time on the synthesis of biodiesel were analysed by utilizing the response surface methodology (RSM). A quadratic response surface equation for calculating fatty acid methyl ester (FAME) content as the objective function was established based on experimental data obtained in accordance with the central composite design. The RSM-based model was then used as the fitness function for genetic algorithm (GA) to optimize its input space. Hybrid RSM-GA predicted the maximum FAME content (91%) at the optimum level of medium variables: methanol ratio to WCO, 4.34; lipase content, 43.6%; water content, 10.22%; and reaction time, 6h. Moreover, the immobilized lipase could be used for four times without considerable loss of the activity.