Esterification of polyglycerol with polycondensed ricinoleic acid catalysed by immobilized Rhizopus oryzae lipase

Abstract

The enzymatic method for synthesising polyglycerol polyricinoleate (PGPR), a food additive named E-476, was successfully carried out in the presence of immobilized Rhizopus oryzae lipase in a solvent-free medium. The great advantage of using the commercial preparation of Rhizopus oryzae lipase is that it is 10 times cheaper than the commercial preparation of Rhizopus arrhizus lipase, the biocatalyst used in previous studies. The reaction, which is really a reversal of hydrolysis, takes place in the presence of a very limited amount of aqueous phase. Immobilization of the lipase by physical adsorption onto an anion exchange resin provided good results in terms of activity, enzyme stability and reuse of the immobilized derivative. It has been established that the adsorption of Rhizopus oryzae lipase on Lewatit MonoPlus MP 64 follows a pseudo-second order kinetics, which means that immobilization is a process of chemisorption, while the equilibrium adsorption follows a Langmuir isotherm. The use of this immobilized derivative as catalyst for obtaining PGPR under a controlled atmosphere in a vacuum reactor, with a dry nitrogen flow intake, allowed the synthesis of a product with an acid value lower than 6 mg KOH/g, which complies with the value established by the European Commission Directive. This product also fulfils the European specifications regarding the hydroxyl value and refractive index given for this food additive, one of whose benefits, as proved in our experiments, is that it causes a drastic decrease in the viscosity (by 50%) and yield stress (by 82%) of chocolate, comparable to the impact of customary synthesised PGPR.