Biocatalytic production of ethyl butyrate from butyric acid with immobilized Candida rugosa lipase on cotton cloth

A Glimpse of the World of Volatile Fatty Acids Production and Application: A review

Sustainable provision of chemicals and materials is undoubtedly a defining factor in guaranteeing economic, environmental, and social stability of future societies. Among the most sought-after chemical building blocks are volatile fatty acids (VFAs). VFAs such as acetic, propionic, and butyric acids have numerous industrial applications supporting from food and pharmaceuticals industries to wastewater treatment. The fact that VFAs can be produced synthetically from petrochemical derivatives and also through biological routes, for example, anaerobic digestion of organic mixed waste highlights their provision flexibility and sustainability. In this regard, this review presents a detailed overview of the applications associated with petrochemically and biologically generated VFAs, individually or in mixture, in industrial and laboratory scale, conventional and novel applications.

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.

Immobilized lipases-based nano-biocatalytic systems - A versatile platform with incredible biotechnological potential

Lipases belong to α/β hydrolases that cause hydrolytic catalysis of triacylglycerols to release monoacylglycerols, diacylglycerols, and glycerol with free fatty acids. Lipases have a common active site that contains three amino acid residues in a conserved Gly-X-Ser-X-Gly motif: a nucleophilic serine residue, an acidic aspartic or glutamic acid residue, and a basic histidine residue. Lipase plays a significant role in numerous industrial and biotechnological processes, including paper, food, oleochemical and pharmaceutical applications. However, its instability and aqueous solubility make application expensive and relatively challenging. Immobilization has been considered as a promising approach to improve enzyme stability, reusability, and survival under extreme temperature and pH environments. Innumerable supporting material in the form of natural polymers and nanostructured materials is a crucial aspect in the procedure of lipase immobilization used to afford biocompatibility, stability in physio-chemical belongings, and profuse binding positions for enzymes. This review outlines the unique structural and functional properties of a large number of polymers and nanomaterials as robust support matrices for lipase immobilization. Given these supporting materials, the applications of immobilized lipases in different industries, such as biodiesel production, polymer synthesis, additives, detergent, textile, and food industry are also discussed.

Optimization of the Enzymatic Synthesis of Pentyl Oleate with Lipase Immobilized onto Novel Structured Support

The term biorefinery is related to the sustainable production of value-added bioproducts and bioenergy from biomass. Esters from fatty acids are important compounds synthesized from by-products of the oleochemical industry. In agreement with the biorefinery concept, it is important to search for catalysts that reduce the consumption of energy and water, using moderate operation conditions and low reaction times. In this work, response surface methodology (RSM) was used to optimize the enzymatic synthesis of pentyl oleate using Candida antarctica lipase B (CALB) immobilized on a polyethylene-aluminum structured support. A factorial design was employed to evaluate the effects of several parameters on the ester yield. To obtain a model with a good fit, an approach to reaction mechanism and enzyme kinetics was taken into consideration. Experimental findings were correlated and explained using equations of a ping-pong bi-bi kinetic model and considering the inhibitory effects of both substrates. The developed model was consistent with the experimental data predicting an increase in pentyl oleate production with increasing temperature and a decrease with higher oleic acid amounts and alcohol to acid molar ratios. This model could be useful in a future industrial application of CALB/LLDPE/Al to minimize the costs in oleochemical biorefineries.

Maximizing the production of butyric acid from food waste as a precursor for ABE-fermentation

The current study reports on the maximization of butyric acid production from food waste using a mixed microbial fermentation. In semi-continuous fermentations the effect of three different pH values (5.5, 7.0 and 9.0), three different temperatures (37°C, 55°C and 70°C) and two levels of hydraulic retention time (HRT, 2days and 6days) on the formation of butyric acid as well as total volatile fatty acid production (tVFA) were investigated. Overall, pH5.5 provided the lowest butyric acid concentrations regardless of the temperature and the HRT. At mesophilic temperature (37°C) alkaline conditions (pH9.0) lead to a strong incline of tVFA as well as butyric acid concentration probably due to a decreased solubilization of the substrate. However, most efficient in terms of butyric acid production was the fermentation conducted at 55°C and pH7 where a butyric acid concentrations of 10.55g/L (HRT 2days) and 13.00g/L (HRT 6days) were achieved. Additional experiments at 70°C showed declining butyric acid production. Increase of the HRT from 2days to 6days provided an increment of butyric acid concentration throughout almost all experimental settings. However, regarding volumetric productivity the increase in concentration does not compensate for the bigger reactor volume required to establish a higher HRT. At pH7 and 55°C the resulting volumetric production rates were 5.27g/L∗d at a HRT 2days and only 2.17g/L∗d at a HRT of 6days.

Lipase catalyzed transesterification of ethyl butyrate synthesis in n-hexane- a kinetic study

Kinetics of lipase catalyzed transesterification of ethyl caprate and butyric acid was investigated. The objective of this work was to propose a reaction mechanism and develop a rate equation for the synthesis of ethyl butyrate by transesterification using surfactant coated lipase from Candida rugosa. The reaction rate could be described in terms of Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The values of kinetic parameters computed were V_max = 2.861 μmol/min/mg; K_m(acid) = 0.0746 M; K_m(ester) = 0.125 M; K_i acid = 0.450 M. This study indicated a competitive enzyme inhibition by butyric acid during lipase catalyzed transesterification reaction. Experimental observations had clearly indicated that the substrates as well as product act as dead-end inhibitors.

Experimental and Modeling Study of Esterification Reaction for Synthesis of Butyl Butyrate: Desirability Function Approach for Optimization and Prediction Comparative Study of RSM and ANN

Butyl butyrate was synthesized by esterification of butyric acid with n-butanol using homogeneous catalyst methanesulfonic acid (MSA). The esterification process was optimized by the application of response surface methodology (RSM) and artificial neural network (ANN). 3 level-4 variables central composite design (CCD) of RSM and MLP 4-9-1 network of ANN was chosen for the experimental design and analysis. The quadratic response model of RSM was optimized using desirability function approach. Effects of independent variables on the yield of butyl butyrate were investigated. Various training algorithm such as IBP, QP, GA, LM, BFGS, and CG was used for training experimental response data for the ANN study. By sensitivity analysis, the relative significance of 36.98 % confirmed that the molar ratio was the main affecting parameter on the yield of butyl butyrate. In prediction comparative study, ANN model was found better than the RSM model with high values of R2 (0.9998) and lower values of RMSE (0.2435), SEP (0.324 %), and AAD (0.0086 %) compared to RSM (R2=0.9862, RMSE=2.3095, SEP=3.076 %, AAD=0.6459 %). The accuracy of the RSM and ANN models were judged by validation test by performing unseen data experiments.

Polyethylenimine: a very useful ionic polymer in the design of immobilized enzyme biocatalysts

This review discusses the possible roles of polyethylenimine (PEI) in the design of improved immobilized biocatalysts from diverse perspectives.

Purification and Immobilization of a Novel Enantioselective Lipase from Tsukamurella tyrosinosolvents for Efficient Resolution of Ethyl 2-(2-oxopyrrolidin-1-yl) Butyrate

A highly enantioselective lipase from Tsukamurella tyrosinosolvents E105 was purified via ultrasonic extraction, precipitation, and chromatographic steps. The enzyme was purified about 38-fold with the recovery yield of 9 % and was confirmed as a dimer protein consisting of two identical subunits with a molecular mass of 24 kDa. The purified lipase was used to catalyze resolution of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid. The maximum activity of such lipase was obtained at pH 7.5, 35 °C, and the highest relative activity (156.80 %) was observed in the presence of 0.5 mM Co²⁺. Subsequently, the lipase was encapsulated within a mixture of 3 % sodium alginate and 0.8 % carrageenan, and then cross-linked with 0.6 % glutaraldehyde to enhance its biocatalytic capability and stability. Comparing with 36.9 % product yield and 97.5 % product ee of free lipase, the highest product yield of 46.3 % and ee of 98.5 % for immobilized lipase were achieved with the presence of 20 mM substrate. In addition, the reusability of immobilized lipase was also investigated, which could maintain 63.7 % of its initial conversion yield after seven repeated batch reactions. Thus, the evaluated enantioselective lipase in this work has a good potential for further industrial application.

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.

Immobilization of Streptomyces thermotolerans 11432 on polyurethane foam to improve production of acetylisovaleryltylosin

In this study, polyurethane foam (PUF) was chemically treated to immobilize Streptomyces thermotolerans 11432 for semi-continuous production of acetylisovaleryltylosin (AIV). Based on experimental results, positive cross-linked PUF (PCPUF) was selected as the most effective carrier according to immobilized cell mass. The effect of adsorption time on immobilized mass was investigated. AIV concentration (33.54 mg/l) in batch fermentations with immobilized cells was higher than with free cells (20.34 mg/l). In repeated batch fermentations with immobilized S. thermotolerans 11432 using PCPUF cubes, high AIV concentrations and conversion rates were attained, ranging from 25.56 to 34.37 mg/l and 79.93 to 86.31 %, respectively. Significantly, this method provides a feasible strategy for efficient AIV production and offers the potential for large-scale production.

Immobilization of lipase on woolen fabrics: enhanced effectiveness in stain removal

The aim of this research was to examine the effectiveness of an enzyme in enhancing the cleaning effectiveness of woolen fabric without addition of any detergent. As a model enzyme, lipase from Pseudomonas fluoresces was immobilized onto a woolen cloth using a unique protocol that involved: chlorination of the wool, adsorbing a polyethyleneimine (PEI) spacer, adsorbing, and cross-linking with glutaraldehyde (GA) followed by adsorption of the lipase. It was determined that for this protocol, the immobilized activity was dependent on the GA solution pH and not on its concentration. The cloth exhibited excellent oily stain removal ability: after being stained with olive oil and stored for 1 day in air at room temperature, the oily stain could be easily removed by 0.05 M pH 8.5 Tris buffer without any detergent addition. This enhanced cleaning was stable also over a period of one month. The activity of the cloth (based on activity assay) dropped considerably over just 15 days storage in air. This therefore likely indicates that the enhanced cleaning seen over an extended storage period may not require as high an enzyme activity. The activity of the immobilized lipase was also very stable when stored under near ideal conditions: when the immobilized cloth was stored in 0.05 M Tris buffer (pH 8.5) for more than 80 days in a refrigerator, more than 80% of the lipase activity remained. Overall, results indicate that this immobilization protocol is a promising step towards producing a woolen fabric with enhanced cleaning properties.

Biosynthesis of ethyl butyrate with immobilized Candida rugosa lipase onto modified Eupergit®C

Lipase from Candida rugosa was immobilized onto the modified Eupergit®C. The support was treated with ethylenediamine and subsequently activated with glutaraldehyde. Enzyme immobilization efficiency was 85%. The optimum pH was close to 6.5 for both the free and immobilized lipase. Immobilized lipase retained its maximum activity in a temperature range of 55 – 60°C. Subsequently, ethyl butyrate synthesis was investigated using immobilized enzyme by esterification of butyric acid with ethanol in solvent-free conditions (23% product yield) and using hexane as a solvent (65% product yield). The acid-alcohol molar ratio and different enzyme amounts were tested as efficient reaction parameters. The biocatalyst maintained 60% of its activity when reused in 8 successive batch reactions in organic solvent. Therefore, the immobilized lipase has demonstrated its potential in practical applications such as short-chain ester synthesis for the food industry.

Parameters Affecting the Performance of Immobilized Enzyme

Enzyme immobilization has been investigated to improve lipase properties over the past few decades. Different methods and various carriers have been employed to immobilize enzyme. However, the application of enzymatic technology in large scale is rarely seen during the industrial process. The main obstacles are a high cost of the immobilization and the poor performance of immobilized lipase. This review focuses on the current status of enzyme immobilization, which aims to summarize the latest research on the parameters affecting the performance of immobilized enzyme. Particularly, the effect of immobilization methods, immobilization carriers, and enzyme loading has been discussed.

Shaping reactor microbiomes to produce the fuel precursor n-butyrate from pretreated cellulosic hydrolysates

To maximize the production of carboxylic acids with open cultures of microbial consortia (reactor microbiomes), we performed experiments to understand which factors affect the community dynamics and performance parameters. We operated six thermophilic (55 °C) bioreactors to test how the factors: (i) biomass pretreatment; (ii) bioreactor operating conditions; and (iii) bioreactor history (after perturbations during the operating period) affected total fermentation product and n-butyrate performance parameters with corn fiber as the cellulosic biomass waste. We observed a maximum total fermentation product yield of 39%, a n-butyrate yield of 23% (both on a COD basis), a maximum total fermentation production rate of 0.74 g COD l(-1) d(-1) and n-butyrate production rate of 0.47 g COD l(-1) d(-1) in bioreactors that were fed with dilute-acid pretreated corn fiber at a pH of 5.5. Pyrosequencing of 16S rRNA genes with constrained ordination and other statistical methods showed that changes in operating conditions to enable dilution of toxic carboxylic acid products, which lead to these maximum performance parameters, also altered the composition of the microbiome, and that the microbiome, in turn, affected the performance. Operating conditions are an important factor (tool for operators) to shape reactor microbiomes, but other factors, such as substrate composition after biomass pretreatment and bioreactor history are also important. Further optimization of operating conditions must relieve the toxicity of carboxylic acids at acidic bioreactor pH levels even more, and this can, for example, be accomplished by extracting the product from the bioreactor solutions.

The future of butyric acid in industry

In this paper, the different applications of butyric acid and its current and future production status are highlighted, with a particular emphasis on the biofuels industry. As such, this paper discusses different issues regarding butyric acid fermentations and provides suggestions for future improvements and their approaches.