Computer-aided control of water activity for lipase-catalyzed esterification in solvent-free systems

Solvent-free enzymatic synthesis and evaluation of vanillyl propionate as an effective and biocompatible preservative

Preservatives are chemicals added to protect products against microbial spoilage, and thus are indispensable for pharmaceuticals, cosmetics, and foods. Due to growing concerns about human health and environments in conventional chemical preservatives, many companies have been seeking safe and effective alternatives that can be produced through environment-friendly processes. In this work, in order to develop effective and safe preservatives from plants, we attempt solvent-free lipase-catalyzed transesterification of vanillyl alcohol with ethyl propionate for the first time. The reaction product, vanillyl propionate was efficiently obtained in a high yield. Unlike vanillyl alcohol and ethyl propionate, vanillyl propionate showed antimicrobial activity. The minimal inhibitory concentration test showed that it exhibited high and broad antimicrobial activity against all the tested microorganisms (Gram-negative and Gram-positive bacteria, yeasts, and molds), which was overall comparable to that of propyl paraben, which is one of the most effective preservatives. It was also found to have even higher antioxidant capacity and biocompatibility with human cells than propyl paraben. Vanillyl propionate, which is a plant-based preservative produced through a green bioprocess, is expected to be successfully applied to various industries thanks to its high antimicrobial and antioxidant effect, and high biocompatibility.

Lipases as Effective Green Biocatalysts for Phytosterol Esters’ Production: A Review

Lipases are versatile enzymes widely used in the pharmaceutical, cosmetic, and food industries. They are green biocatalysts with a high potential for industrial use compared to traditional chemical methods. In recent years, lipases have been used to synthesize a wide variety of molecules of industrial interest, and extraordinary results have been reported. In this sense, this review describes the important role of lipases in the synthesis of phytosterol esters, which have attracted the scientific community’s attention due to their beneficial effects on health. A systematic search for articles and patents published in the last 20 years with the terms “phytosterol AND esters AND lipase” was carried out using the Scopus, Web of Science, Scielo, and Google Scholar databases, and the results showed that Candida rugosa lipases are the most relevant biocatalysts for the production of phytosterol esters, being used in more than 50% of the studies. The optimal temperature and time for the enzymatic synthesis of phytosterol esters mainly ranged from 30 to 101 °C and from 1 to 72 h. The esterification yield was greater than 90% for most analyzed studies. Therefore, this manuscript presents the new technological approaches and the gaps that need to be filled by future studies so that the enzymatic synthesis of phytosterol esters is widely developed.

A water-dependent kinetics guide for complex lipase-mediated synthesis of biolubricants in a water activity control reactor

A water-dependent kinetic model for a lipase-mediated reaction with multiple substrates and products in a water activity control reactor was developed.

Kinetic Model with Effect of Water Content for Enzyme-Catalyzed Citronellyl Laurate Esterification Process

A kinetic model with effect of water content for enzyme-catalyzed citronellyl laurate was developed. These models incorporate the combined influences of established kinetics model with the function model on the effect of initial water content with kinetic parameters. The model development was carried out by performing a linear and nonlinear regression based on the behavior of the kinetic parameter profiles and validated with experimental data. Using the developed models, the influence of water content towards the enzyme-catalyzed initial rate of reaction was theoretically explained. It has been shown that the proposed model have good agreement between experimental data and intends to capture the effect of water content towards the conversion of ester. With this model, the optimal value of initial water content for this process could be estimated.

Lipases in lipophilization reactions

Lipases are used in various sectors, as pharmaceutical, food or detergency industry. Their advantage versus classical chemical catalysts is that they exhibit a better selectivity and operate in milder reaction conditions. Theses enzymes can also be used in lipophilization reactions corresponding to the grafting of a lipophilic moiety to a hydrophilic one such as sugar, amino acids and proteins, or phenolic compounds. The major difficulty to overcome in such enzyme-catalyzed reaction resides in the fact that the two involved substrates greatly differ in term of polarity and solvent affinity. Therefore, several key parameters are to be considered in order to achieve the reaction in satisfactory kinetics and yields. The present review discusses the nature of such parameters (eg solvent nature, water activity, chemical modification of substrates) and illustrates their effect with examples of lipase-catalyzed lipophilization reactions of various sugar, amino acids or phenolic derivatives.

A water activity control system for enzymatic reactions in organic media

A water activity control system for enzymatic synthesis in organic media, for litre-scale reactors has been constructed. Water activity, a(w), is a key factor when using enzymes in non-conventional media and the optimum value varies for different enzymes. The control system consists of a water activity sensor in the headspace of a jacketed glass reactor (equipped with narrow steel tubes to introduce air), gas-washing bottles containing blue silica gel (a(w)=0) and water (a(w)=1), a PC to monitor water activity and a programmable logic controller (PLC) to control the water activity. The system was evaluated by adjusting water activity in the medium, with a deviation from the set point of less than +/-0.05. Synthesis of cetyl palmitate, under controlled water activity and catalysed by two different lipase preparations, namely, Novozym 435 (immobilised Candida antarctica lipase B) and immobilised Candida rugosa lipase, were also performed. Novozym 435 catalyses reactions very well at extremely low water activity while C. rugosa lipase shows low activity for a(w)<0.5.

Real time measurement and control of thermodynamic water activities for enzymatic catalysis in hexane

The esterification reaction of geraniol with acetic acid catalyzed by immobilized Candida antarctica lipase B was studied in hexane using a pervaporation-assisted batch reactor. The effect of thermodynamic water activity (a(w)) on the initial reaction rate was investigated at a(w) ranging from 0.02 to 1.0. The a(w) was monitored on-line in real time. a(w) was actively controlled throughout the reaction by using highly water-selective membrane pervaporation. This novel combination of a(w) sensing and control eliminates changes in a(w) during the reaction even in the initial phase of relatively rapid water release during an esterification. No chemicals are introduced for a(w) control, and no purge gases or liquids are needed. A maximum in the initial reaction rate was found approximately at a(w)=0.1. The initial reaction rate declined quickly at higher a(w), and dropped precipitously at lower a(w).

Mild, Solvent-Free ω-Hydroxy Acid Polycondensations Catalyzed byCandidaantarcticaLipase B

Immobilized Candida antarctica Lipase B (Novozyme-435) was studied for bulk polyesterifications of linear aliphatic hydroxyacids of variable chain length. The products formed were not fractionated by precipitation. The relative reactivity of the hydroxyacids was l6-hydroxyhexadecanoic acid approximately 12-hydroxydodecanoic acid approximately 10-hydroxydecanoic acid (DPavg congruent with 120, Mw/Mn <or = 1.5, 48 h, 90 degrees C) > 6-hydroxyhexanoic acid (DPavg congruent with 80, Mw/Mn < or = 1.5, 48 h, 90 degrees C). Remarkable improvements in molecular-weight buildup resulted from leaving water in the reaction. By 4 h, without application of vacuum, the DPavg for 12- and 16-carbon hydroxyacids was about 90. In contrast, with identical substrates and water removal, the DPavg at 4 h was about 23. Large differences in the molecular-weight build up of 12-hydroxydodecanoic acid were observed for catalyst concentrations (%-by-wt relative to monomer) of 0.1, 0.5, 1, and 10. Nevertheless, by 24 h, with 1% catalyst containing 0.1% lipase, poly(12-hydroxydodecanoic acid) with Mn 17 600 was formed. For 12-hydroxydodecanoic acid polymerization at 90 degrees C, the catalyst activity decreased by 7, 18, and 25% at reaction times of 4, 24, and 48 h, respectively. Furthermore, the retention of catalyst activity was invariable as a function of the substrates used.

Computer-aided real-time estimation of reaction conversion for lipase-catalyzed esterification in solvent-free systems

Real-time conversion estimation through macroscopic balancing was investigated for enzymatic esterification reactions in a solvent-free system. In principle, the conversion of ester synthesis can be determined from the amount of water produced by the reaction because water is formed as a by-product in the same molar ratio as the product. In this study, we show that the water production rate, and thereby the reaction conversion, can be estimated on-line from measurements of the relative humidity of the inlet and outlet air and the material balances of water in the system. In order to test the performance of the real-time conversion estimation method, the lipase-catalyzed esterification reaction of n-capric acid and n-decyl alcohol in solvent-free media was conducted while controlling the water activity at various values. When the reaction conversions estimated on-line were compared with those analyzed off-line by gas chromatography, good agreement was obtained: the average mean absolute error was +/- 2.4% of the reaction conversion despite the simplicity of the method. The on-line estimation method presented here requires no expensive or complicated analytical instruments and no sampling of reaction medium. It can be used for monitoring nonaqueous enzymatic reactions where water is produced or consumed during reaction.

Lipases as practical biocatalysts

Lipases are the most used enzymes in synthetic organic chemistry, catalyzing the hydrolysis of carboxylic acid esters in aqueous medium or the reverse reaction in organic solvents. Recent methodological advancements regarding practical factors affecting lipase activity and enantioselectivity are reviewed. Select practical examples concerning the use of lipases in the production of chiral intermediates are also highlighted.