Estudio de procesos de biosíntesis enzimática de ésteres aromáticos para su uso en cosméticos naturales

Abstract

This Doctoral Thesis is based on the hypothesis that it is possible to perform the biocatalytic synthesis of different aromatic additives to be used in what might be classified as "natural" cosmetic products by means of more environmentally friendly processes. In addition, this study proposes a kinetic model for the reactions involved, and aims to establish a systematic method to determine the kinetics of the process and understand how the enzymatic synthesis reactions take place. To this end, the two main aromas selected for this study are 2-phenylethyl acetate, found in the aroma of roses, and 1-phenylethyl acetate, found in the aroma of gardenias. Both acetates are synthesized enzymatically by transesterification reactions. The specific objectives of this Doctoral Thesis are: - To select an experimental device to achieve the synthesis of aromatic esters by enzymatic transesterification. - To study the influence of various reagents and various commercial biocatalysts in the process of obtaining these aromas. - To study the influence of the variables in the system which have the biggest impact on the efficiency of the reaction, but only for those enzymes/substrates that have given good results. - To propose kinetic models that can predict what the progress of different reactions will be over time, adjusting the experimental data to those models. - To carry out the pertinent kinetic studies in order to obtain the kinetic parameters that make possible the simulation of the system at other levels. To achieve these specific objectives, the methodology used in this research has been developed on three levels: On a theoretical-conceptual level, all activities related to the stages of the approach adopted for this research and the formulation of hypothesis are developed. This level concludes planning the work to be carried out on the following levels. On a technical-methodological level, the activities carried out in the laboratory in order to obtain a collection of experimental data are developed. The activities carried out on this level are divided in two groups, those corresponding to the operational method of the tests to be carried out, and those corresponding to the analytical method used to obtain the necessary information. On a statistical-analytical level, the activities to statistically interpret the data are developed. These are used to analyse, study and obtain the conclusions of the research. Based on the results, a kinetic model is proposed and checked to adjust the theoretical data to the actual data obtained. The most important conclusions included in this Doctoral Thesis are the following: - The discontinuous tank reactor is an experimental device suitable for the biosynthesis of the esters of 2-phenylethyl acetate and 1-phenylethyl acetate. - The commercial immobilized biocatalyst Novozym¿ 435 presents the best results in the synthesis of both esters, under the studied conditions. - Under the same reaction conditions, the synthesis of 2-phenylethyl acetate has better results than the synthesis of 1-phenylethyl acetate. The effect of the catalyst concentration on the conversion obtained has also been studied. - A kinetic model based on the rate equation for the Bi Bi Ping-Pong mechanism provides a simplified equation that predicts the progress of the reaction based on time. - The most important sets of intrinsic kinetic constants in the synthesis by enzymatic transesterification of these two esters have been obtained. - It has been possible to adjust the experimental data to the proposed equation by presenting good correlation coefficients. - The complete equation of the kinetic model allows the simulation of the process to better understand what the influence of the most important variables in the system is.