Lipase applications in oil hydrolysis with a case study on castor oil: a review.

Lipase (triacylglycerol acylhydrolase) is a unique enzyme which can catalyze various types of reactions such as hydrolysis, esterification, alcoholysis etc. In particular, hydrolysis of vegetable oil with lipase as a catalyst is widely studied. Free lipase, lipase immobilized on suitable support, lipase encapsulated in a reverse micelle and lipase immobilized on a suitable membrane to be used in membrane reactor are the most common ways of employing lipase in oil hydrolysis. Castor oil is a unique vegetable oil as it contains high amounts (90%) of a hydroxy monounsaturated fatty acid named ricinoleic acid. This industrially important acid can be obtained by hydrolysis of castor oil. Different conventional hydrolysis processes have certain disadvantages which can be avoided by a lipase-catalyzed process. The degree of hydrolysis varies widely for different lipases depending on the operating range of process variables such as temperature, pH and enzyme loading. Immobilization of lipase on a suitable support can enhance hydrolysis by suppressing thermal inactivation and estolide formation. The presence of metal ions also affects lipase-catalyzed hydrolysis of castor oil. Even a particular ion has different effects on the activity of different lipases. Hydrophobic organic solvents perform better than hydrophilic solvents during the reaction. Sonication considerably increases hydrolysis in case of lipolase. The effects of additives on the same lipase vary with their types. Nonionic surfactants enhance hydrolysis whereas cationic and anionic surfactants decrease it. A single variable optimization method is used to obtain optimum conditions. In order to eliminate its disadvantages, a statistical optimization method is used in recent studies. Statistical optimization shows that interactions between any two of the following pH, enzyme concentration and buffer concentration become significant in presence of a nonionic surfactant named Span 80.

Mixed micelles and bicontinuous microemulsions: Promising media for enzymatic reactions.

Enzymes, the natural catalysts, replace catalysts of chemical origin in a wide spectrum of reactions and generally work under environment friendly conditions. Various strategies are adopted to modify catalytic activities of enzymes further, of which one is application of novel reaction medium. This work reviews applicability of novel media like mixed micelles and bicontinuous microemulsions in enzymatic reactions and points out their capability to play bigger roles in enzyme catalysis. Ionic reverse micelles reduced catalytic activities of enzymes through denaturation. Addition of nonionic surfactant to these reverse micelles led to corresponding mixed micelles and thus restored or sometimes enhanced catalytic abilities of enzymes. Mixed micelles comprising of two nonionic surfactants, bicontinuous microemulsion containing two anionic surfactants also acted as efficient reaction media for enzymes. Even a cationic/anionic/nonionic mixed micelle was found to increase activity of enzyme. Mixed micelles and bicontinuous microemulsions comprising of anionic and zwitterionic surfactants augmented enzyme catalysis. Mixed micelles and bicontinuous microemulsions containing ionic liquid and surfactant also had critical impact on enzyme catalysis. Catalytic abilities of enzymes altered significantly in substrate/surfactant and bile salt/surfactant mixed micelles. Concentrations of individual surfactant, molar ratio of surfactants, and molar ratio of water to total surfactants had notable impacts on enzyme catalysis in those media.

Lipase Catalysis in Presence of Nonionic Surfactants.

Lipase can catalyze varieties of reactions at the interface of aqueous and organic phase. Among various alternatives to modify catalytic performance of lipase, the addition of surfactants, particularly nonionic surfactants, has been widely studied. Low concentrations of nonionic surfactants augment lipase catalysis; on increasing surfactant concentration, often the catalytic performance decreases. Mole ratio of water to (nonionic) surfactant also has a profound effect on lipase activity. Catalytic abilities of some lipases are either enhanced or reduced in the presence of all nonionic surfactants of the same type, whereas for some other lipases, nonionic surfactants of the same type have mixed effect. Nonionic surfactant even changes substrate specificity of lipase. Water-in-ionic liquid microemulsion involving nonionic surfactant often performs better than other systems in improving catalytic ability of lipase. Tween and Triton surfactants often enhance enantiomeric separation catalyzed by lipase. Nonionic surfactants significantly affect activities of immobilized lipase, being present either as a component during immobilization or as a component in reaction medium. Lipases coated with nonionic surfactants act better than reverse micelles and microemulsions containing lipase. Thus, nonionic surfactants help lipase catalyzed processes in various media to enhance production of useful compounds like flavor ester, structured lipids, optically pure compounds, and noncrystalline polymers.

Surfactant enhanced ricinoleic acid production using Candida rugosa lipase.

In this study, ricinoleic acid was produced on surfactant enhanced castor oil hydrolysis using Candida rugosa lipase. The most effective surfactant was Span 80. Employing fractional factorial design, the most suitable temperature and surfactant concentration were found to be 31 degrees C and 0.257% (w/w in buffer) respectively whereas pH, enzyme concentration, buffer concentration and agitation were identified as the most significant independent variables. A 2(4) full factorial central composite design was applied and the optimal conditions were found to be pH 7.0, enzyme concentration 7.42 mg/g oil, buffer concentration 0.20 g/g oil and agitation 1400 rpm with the maximum response of 76% in 4 h. The most important variable was pH, whereas enzyme and buffer concentrations also showed pronounced effect on response. This is the first report on the application of response surface methodology for optimizing surfactant enhanced ricinoleic acid production using C. rugosa lipase.

Maximization of bioconversion of castor oil into ricinoleic acid by response surface methodology.

In this study, response surface methodology was applied to optimize process variables like temperature, pH, enzyme concentration (mg/g oil), and buffer concentration (g/g oil) for hydrolysis of castor oil using Candida rugosa lipase. A 2(4) full factorial central composite design was used to develop the quadratic model that was subsequently optimized and the optimal conditions were as follows: temperature 40 degrees C, pH 7.72, enzyme concentration 5.28 mg/g oil, buffer concentration 1g/g oil and there was 65.5% conversion in 6 h. These predicted optimal conditions agreed well with the experimental results. This is the first report on the application of response surface methodology in castor oil hydrolysis using C. rugosa lipase with higher percentage conversion in 6 h.