Enhanced Lipase – Catalyzed Triglyceride Hydrolysis

Abstract

The use of microbial lipases for the hydrolysis of natural oils such as triglyceride esters is a green alternative to conventional high temperature, high pressure steam-based technologies and other chemical synthesis. The hydrolytic splitting of the esters is necessary for the downstream production of high value chemical products such as coatings, adhesives, and high-performance personal care products. Deployment of enzymatic methods enables conversions to be achieved at close to ambient temperature and pressure with positive impacts on energy utilization and product purity. Enzymatic splitting of triglyceride esters is limited often by slow kinetics due to mass transfer limitations and by challenges of economic enzyme recycling. Immobilization of lipases on a solid carrier or support has proven to be an effective alternative method and, in some cases, considered superior to the use of lipases in aqueous media. Enhanced thermal and chemical stability, activity, recoverability, and reusability of the biocatalyst (lipase) are all potential advantages of immobilization. Efficacy of immobilization depends significantly on the mechanical integrity of the support, availability, and adjustable characteristics such as porosity, surface area, particle size a functional groups present, and the type of lipase used. The performance of microbial lipase derived from Candida rugosa immobilized onto polymeric methacrylate-based resins with no surface functionalization (ECR1030M), epoxy & butyl functionalization (ECR8285) and octadecyl functionalization (ECR8806M) supplied by Purolite® LifetechTM Resins Corporation was studied for triglyceride hydrolysis. The main mechanism involved in lipase immobilization was adsorption using hydrophobic interactions. Sizing of protein using the dynamic light scattering technique suggested immobilization was surface dominant. The resins were characterized using FT-IR spectrometry, N2 adsorption, contact angle measurements and scanning electron microscopy. Continuously stirred batch reactors operated at 100 RPM were used to compare the performance of the immobilized lipase by measuring the release of free fatty acids (FFA). Octadecyl functionalized methacrylate polymer resins showed superior performance. Comparing the octadecyl functionalized resins with un-functionalized methacrylate resins, a four-fold increase in activity retention was observed in multicycle experiments. Epoxy & butyl functionalized resins showed lower performance compared to octadecyl functionalized resin but higher than un-functionalized methacrylate resins. Performance in the presence of crosslinking agents such as, Glutaraldehyde, (3-Aminopropyl) triethoxysilane and itaconic acid applied during the immobilization protocol for methacrylate based polymeric resins and superior performance was observed in the case of itaconic acid on functionalized methacrylate resins. Prior work has shown that mass transfer rates and reaction rates can be intensified by increasing interfacial area for lipase catalyzed triglyceride hydrolysis using electrostatic spray reactors. However, the possible effect of oriented external electrical field on the lipase catalytic activity has hitherto not been considered. The performance of microbial lipase derived from Candida rugosa in aqueous solutions was analyzed in the presence of a steady DC externally applied electrical voltage. The reaction was conducted in three different batch type reactors: (1) In a quiescent (fixed interface) reactor; (2) In a stirred tank batch reactor, and (3) In a recirculating tubular flow reactor. It was concluded that the oriented external electrical field has a positive effect on all three-reactor system studied, showing reaction rate enhancement, independent of interfacial area. Further studies conducted using reverse polarity, increased electrode distance and for immobilized lipase system has shown that lipase undergoing conformational changes due to an oriented external electrical field is the main driving mechanism for this noted enhanced performance.